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  • Origin of scattering defect observed in large diameter Ti:Al2O3 crystals grown by the Kyropoulos technique
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-27
    G. Sen; G. Alombert Goget; V. Nagirnyi; I. Romet; T.N. Tran Caliste; J. Baruchel; J. Muzy; L. Giroud; K. Lebbou; Th. Duffar

    Large diameter Ti-doped sapphire single crystals grown by the Kyropoulos technique along the A-axis, show detrimental light scattering close to the central C-plane. Thermo-luminescence measurements evidence that this defect is associated to a high level of oxygen vacancies. X-ray topography and Rocking Curve Imaging were performed. They show that the dislocation number is very small where scattering occurs, compared to the rest of the crystal, in agreement with results of numerical modelling of thermo-elastic stresses during crystal growth. A model is proposed in order to explain the scattering effect, based on the precipitation of nano-voids from vacancies in the absence of dislocations.

    更新日期:2020-01-27
  • Growth and Properties of Large Aperture YCOB Crystal for NLO Application
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-27
    Xiaoniu Tu; Sheng Wang; Kainan Xiong; Yanqing Zheng; Erwei Shi

    Yttrium calcium oxyborate (YCOB) is one of commonly used nonlinear optical (NLO) crystals with good thermal and NLO properties. In this work, large YCOB crystals without cleavage were grown by the Bridgman (Br) method, and crystal element with the size of 102 mm×100 mm×18 mm was harvested for the first time, which is the largest aperture up to now to the best of our knowledge. The optical absorption, homogeneity and bulk laser induced damage threshold (LIDT) were analyzed detailedly. The type-I phase-matched nanosecond (ns) second-harmonic generation (SHG) and picosecond (ps) SHG in YCOB XZ plane (29.1°, 180°) were also demonstrated. The highest SHG conversion efficiency of 73% were achieved from a fundamental source with 2 Hz repetition rate and 50 ps pulse duration at 1053 nm in the 10 mm long YCOB Crystal. It is believed that based on this work, YCOB crystal elements with high quality and large aperture will be used in high power laser system in the near future.

    更新日期:2020-01-27
  • Epitaxial Regrowth and Hole Shape Engineering for Photonic Crystal Surface Emitting Lasers (PCSELs)
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-27
    Kevin J. Reilly; Akhil Kalapala; Seuongwon Yeom; Sadhvikas J. Addamane; Emma Renteria; Weidong Zhou; Ganesh Balakrishnan

    In the present research, epitaxial regrowth by molecular beam epitaxy (MBE) is investigated as a fabrication process for void-semiconductor photonic crystal (PhC) surface emitting lasers (PCSELs). The PhC is patterned by electron beam lithography and inductively coupled plasma (ICP) etch and is subsequently regrown by molecular beam epitaxy to embed a series of voids in bulk semiconductor. Experiments are conducted to investigate the effects of regrowth on air-hole morphology. The resulting voids have a distinct teardrop shape with the radius and depth of the etched hole playing a very critical role in the final regrown void’s dimensions. We demonstrate that specific hole diameters can encourage deposition to the bottom of the voids or to their sidewalls, thus allowing us to engineer the shape of the void more precisely as is required by the PCSEL design. A 980 nm InGaAs quantum well laser structure is optimized for low threshold lasing at the design wavelength and full device structures are patterned and regrown. An optically pumped PCSEL is demonstrated from this process.

    更新日期:2020-01-27
  • Quantum dot molecule formation in Si-Ge heteroepitaxy on pit–patterned Si(001) substrate : A theoretical study
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-27
    Monika Dhankhar; Madhav Ranganathan

    Quantum dot molecules refer to nanostructures consisting of four quantum dots around a central pit. These are observed to form in Si-Ge heteroepitaxy and are considered an alternative to quantum dots for strain relaxation. Here we use numerical simulations of a continuum model of strained heteroepitaxy to show the spontaneous formation of quantum dot molecules in thick Si0.5Ge0.5 films grown on pit–patterned Si substrates. The route to their formation first involves a quantum dot in the pit, followed by removal of material from the pit to form quantum dot molecules. These molecules are formed for smaller pit widths, whereas larger pit widths tend to create a ridged surface. A mature single–walled quantum dot molecule has a typical size of about 220 nm. On reducing the wavelength of the original pit–pattern, we notice that multiple–walled quantum dot molecules form, due to the interactions with other nearby molecules. Our results broadly agree with experiment and suggest that QDM formation on patterned substrates does not necessarily have a nucleation barrier and can take place following the usual evolution of the Asaro–Tiller–Grinfeld instability.

    更新日期:2020-01-27
  • Hydrothermal Growth of BaSnO3 Single Crystals For Wide Bandgap Applications
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-27
    Rylan J. Terry; Nick Combs; Colin D. McMillen; Susanne Stemmer; Joseph W. Kolis

    A method for the synthesis of single crystals of BaSnO3 is reported. The growth employs a hydrothermal process using simple Ba(OH)2 and SnO2 powders in water at 650˚C and 140 MPa, with 5 M CsOH mineralizer in welded inert metal liners. Solubility studies indicate that the crystals have positive solubility coefficients that increase with temperature and mineralizer concentration in the growth regimes investigated. The tetravalent tin ions are somewhat aggressive toward the inert metal liners, especially silver and gold, requiring platinum liners for longer term growth runs. The (110) and (100) faces are commonly observed on the as-grown crystals. The crystals are thermally and chemically stable and can be readily polished as substrates for subsequent epitaxial growth. Crystals that are n-doped (La:BaSnO3) can be grown by the addition of the desired amount of La2O3 to the initial feedstock. The band gap for this hydrothermally-grown BaSnO3 was measured using the Tauc plot method to be 2.94 eV, with approximately 0.3 eV shift to higher energy upon n-doping.

    更新日期:2020-01-27
  • Growth of GaN layers using Ga2O vapor synthesized from Ga2O3 and carbon
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-27
    Akira Kitamoto; Yohei Yamaguchi; Shintaro Tsuno; Keiju Ishibashi; Yoshikazu Gunji; Masayuki Imanishi; Mamoru Imade; Masashi Yoshimura; Masahiko Hata; Masashi Isemura; Yusuke Mori

    In this study, we grew GaN layers using Ga2O vapor synthesized from Ga2O3 powder and carbon powder. To precisely regulate the growth rate of the GaN layers, we controlled the supply rate of Ga2O vapor by controlling the reaction rate between Ga2O3 and carbon. The results showed that the growth rate increased linearly with partial pressure of Ga2O vapor and that GaN layers with the smooth (0001) surface could be grown at 10 – 49 μm/h. X-ray diffraction (XRD) measurements revealed that the epitaxial layer was single-crystalline GaN and the FWHM of the GaN epitaxial layers ranged from 51 to 105 arcsec, confirming that the epitaxial layers inherit the high crystallinity of the seed substrates. Secondary ion mass spectrometry (SIMS) analysis showed that the oxygen concentrations in the epitaxial layers at the growth rates of 15 and 49 μm/h were 2.0×1017 and 2.5×1019 atoms/cm3, respectively. The carbon concentration in the epitaxial layers was below the detection limit. These values were the lowest seen in crystals obtained by the conventional technique using Ga2O vapor. These results show that this method, using Ga2O vapor produced by the reaction of Ga2O3 with carbon, has the potential to grow GaN crystals with high crystallinity and high purity by promoting the smoothness of the (0001) surface.

    更新日期:2020-01-27
  • Growth of heavily-doped Germanium single crystals for mid-Infrared applications
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-25
    R. Radhakrishnan Sumathi; Nikolay Abrosimov; Kevin-P. Gradwohl; Matthias Czupalla; Jörg Fischer

    In the growth of germanium (Ge) single crystals by Czochralski (Cz) method, a novel gas-phase doping procedure has been suggested, to obtain heavily doped, both n-type (phosphorous) and p-type (boron) semiconducting crystals. The crystals were grown using the so-called “mini-Cz” technique and the pulled crystals are characterized for their structural and electrical properties. A narrow full width at half maximum (FWHM) of the X-ray diffraction rocking curves obtained for both symmetric (400) reflection (14 arcsec) and asymmetric (311) reflection (11 arcsec) indicate good crystalline quality. In addition, the grown crystals have a low dislocation density (etch pit density of ≈104 cm-2) without hot-zone optimization. Doping concentrations of up to 3 x 1018 cm-3 have been obtained so far, which implies that gas-phase doping is a viable route and may solve some of the conventional doping issues when using solids as dopants in the Cz melt. We also report here high doping of antimony (Sb) using a solid dopant source. Non-flat solid-liquid interface of the Sb-doped crystals during the growth process, as characterized by the typical ring structure of the growth striations, has been seen in lateral photovoltage scanning (LPS) measurements.

    更新日期:2020-01-26
  • Facile synthesis and characterization of zinc selenide nanoparticles in aqueous solution at room temperature
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-25
    Hyun Seon Hong; Mi-So Kim; Eun Kyung Byun; You Lim Lee

    Nano-sized zinc selenide (ZnSe) particles were successfully fabricated using a chemical synthesis technique, in aqueous solution at room temperature. Sodium borohydride was used as a reagent for reduction and the Zn/Se ratio for the synthesis was varied to evaluate its influence on the microstructure and optical properties of the nanoparticles. The ZnSe particles thus fabricated were analyzed by X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis) and photoluminescence spectroscopy (PL). Analysis of the XRD patterns showed that single-phase ZnSe was successfully synthesized, and the particle size based on TEM confirmed that the particles were nano-sized. The ZnSe nanoparticles absorbed UV-Vis light with wavelength shorter than 460 nm, the absorption wavelength of bulk ZnSe. As the Zn/Se ratio increased, the absorption edge wavelength in the UV-Vis spectra gradually shifted to 420 nm. This blue shift was estimated to be due to the broadening of absorption curves of the nanoparticles toward the shorter wavelength. The synthesized nanoparticles showed good structural and light absorption properties suggesting that ZnSe nanoparticles can be fabricated at room temperature without using organic solvents.

    更新日期:2020-01-26
  • Molecular beam epitaxy growth and characterization of interband cascade infrared detectors on GaAs substrates
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-22
    Ł. Kubiszyn; D. Benyahia; K. Michalczewski; K. Hackiewicz; A. Kębłowski; P. Martyniuk; J. Rutkowski; J. Piotrowski

    Interband cascade infrared detectors (IB CIDs) are devices built from multiple cells connected in series using specially designed interband tunneling and relaxation regions. Such design enables effective collection of photogenerated carriers and is particularly beneficial in the case of short diffusion length in absorber’s material. In this work, we report on the growth and characterization of type-II InAs/GaSb superlattices IB CIDs on highly lattice-mismatched (001) GaAs substrates for mid-wave range. IB CIDs are characterized by high resolution X-ray diffraction, dark current and current responsivity. The performance of devices with different number of stages is discussed. Devices with 50% cut-off wavelength at 5.3 μm exhibit at temperature 300 K peak detectivity of 3.6×108 cmHz1/2W-1.

    更新日期:2020-01-22
  • Epitaxial Growth of GaN/Ga2O3 and Ga2O3/GaN Heterostructures for Novel High Electron Mobility Transistors
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-22
    Stefano Leone; Roberto Fornari; Matteo Bosi; Vincenzo Montedoro; Lutz Kirste; Philipp Doering; Fouad Benkhelifa; Mario Prescher; Christian Manz; Vladimir Polyakov; Oliver Ambacher

    Heterostructures made of GaN and ε-Ga2O3 epitaxial layers may be very interesting because they could exploit the high electron mobility of GaN combined with the ferroelectric character of ε-Ga2O3. We have explored the possibility of using ε-Ga2O3 templates, deposited by metalorganic chemical vapor deposition on sapphire substrates, in order to reduce the lattice mismatch of GaN with sapphire. Considering that ε-Ga2O3 is metastable and undergoes a first phase transition at around 700 °C, the GaN layers were deposited at two different temperatures (690°C, 1050 °C). Preliminary electrical and SIMS investigations have evidenced the diffusion of oxygen from the ε-Ga2O3 to the GaN epitaxial layer, which results in an n-type conductivity and a sheet resistance as low as 70 Ohm/sq in a 1 μm thick GaN layer. The rocking curve of the GaN layers grown ε-Ga2O3/sapphire at standard high temperature (1050°C) indicates a crystal quality worse than for GaN deposited directly on sapphire. In parallel, we studied the nucleation of ε-Ga2O3 on GaN templates. We evidenced that ε-Ga2O3 nucleates in 3D islands on the surface of GaN grown on on-axis sapphire, with coalescence taking place as the layer grows thicker. The use of off-cut sapphire substrates, instead, permits to inhibit islands formation, resulting in a smoother layer. The possibility of obtaining uniform and very thin ε-Ga2O3 layers on GaN layers opens interesting possibilities for the development of novel high electron mobility transistors (HEMT).

    更新日期:2020-01-22
  • In situ measurements of solid-phase kinetic growth during slag isothermal crystallisation
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-21
    Chong He; Alexander Ilyushechkin; San Shwe Hla

    In this work we investigated the isothermal crystallisation of spinel and anorthite phases during slag viscosity measurements. Our results show that solid precipitation time and solid-phase growth rates are significantly affected by slag viscosity and the degree of supercooling. Through scanning electron microscopy and electron probe microanalysis of quenched-slag phase compositions and analysis of the viscosity changes during crystallisation, we have determined the kinetics of solid phase growth and identified differences in spinel and anorthite crystals growth.

    更新日期:2020-01-22
  • Centimetric CrSi2 crystal grown by the Vertical Gradient Freeze method
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-21
    A. Moll; S. Laborde; F. Barou; M. Beaudhuin

    CrSi2 ingots were grown by the Vertical Gradient Freeze (VGF) method in silica (SiO2) crucibles with boron nitride (BN) coating and in pyrolytic boron nitride (pBN) crucibles in order to minimize the sticking and the reaction with the molten Cr-Si alloy. High quality chromium disilicide single crystal was obtained with a mosaicity of 1 to 2° using pBN crucible with a thermal gradient of 0.6 K/mm and a growth rate of 10 mm/h. To recycle the crucibles and so to reduce the production costs, pBN crucibles were cleaned with hydrofluoric acid solution. As a result of this treatment, it was not possible to obtain CrSi2 single crystals due to a modification of the crucible surface and the subsequent increase of boron compounds in the melt during the growth. The effect of the growth conditions on the microstructure of polycrystalline sample was also investigated using the texture analysis technique.

    更新日期:2020-01-22
  • Precipitation of multilayer graphene directly on gallium nitride template using Tungsten capping layer
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-18
    Jumpei Yamada; Yuki Ueda; Takahiro Maruyama; Shigeya Naritsuka

    The direct growth of graphene was investigated with precipitating graphene on a GaN template at various temperatures. In the method, a carbon source and catalyst were firstly deposited, and the sample was annealed to precipitate graphene. Tungsten capping layer was deposited on the surface to suppress the graphene precipitating to the sample surface. Consequently, the graphene was precipitated at the interface between the catalyst and the GaN template. After the removal of the catalyst, the graphene was successfully obtained on the GaN template. The Raman D/G ratio of the graphene decreased with increasing the annealing temperature. At 700 °C, fine graphene was obtained on the GaN template while maintaining the flatness and smoothness of the GaN surface. XRD and XPS measurements were also performed to investigate the precipitation of the graphene in detail.

    更新日期:2020-01-21
  • Composition, structure and morphology of ZNO–CO3O4 ceramic targets in the process of pulsed laser thin film deposition
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-17
    A.S. Kuz'mina; A.A. Lotin; N.A. Strokin; M.P. Kuz'min; A.V. Kazantsev

    This paper presents the results of the study of the composition, structure and morphology of ZnO–Co3O4 ceramic targets before and after laser ablation by the KrF excimer laser. X-ray diffraction analysis showed that the composition of the targets changes under the thermal effects of laser radiation: a new phase of CoO of the cubic structure is formed (a = 4.25 Å). The radial distribution of elements in the ZnO–Co3O4 targets after ablation by the KrF excimer laser was discovered for the first time. The atomic concentration of cobalt in the center was determined to be several times higher than its concentration at the edge of the targets. This can be explained by the thermal model of laser-semiconductor interaction. The morphology of the targets surface after the laser ablation was discovered to undergo significant changes. Pulsed nanosecond laser radiation induces the formation of center-oriented cone-shaped structures and micro-whiskers on the target surface. It was determined that the higher is the concentration of doping impurities in the target, the greater is the number of structures observed on the surface. The formation of “cones” and microwhiskers is explained by the generalized growth model of the vapor–liquid–crystal mechanism.

    更新日期:2020-01-17
  • Numerical simulation of the flow and mass transport during the growth of ADP crystals by additional stirrer
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-17
    Hang Liu; Mingwei Li; Pengfei Wang; Zhitao Hu; Huawei Yin

    A stirrer is added to the traditional rotating crystal growth system of ammonium dihydrogen phosphate (NH4H2PO4, ADP), aiming at effectively utilizing the convection to improve the mass transfer and the distribution homogeneity of the supersaturation on the crystal face. 3D numerical simulation on flow and surface supersaturation distribution under different conditions is performed employing the finite-volume method, and the effect of flow on the surface supersaturation distribution is analyzed in detail. Compared with the traditional rotating-crystal system, the introduction of a stirrer can produce stronger axial flow and accordingly improve the magnitude and distribution homogeneity of the surface supersaturation, which is favorable to grow high quality crystals. As the stirrer rotation rate increases, the magnitude of the axial flow velocity increases, resulting in a reduction of the thickness of the solute boundary layer and an increase of the supersaturation on the crystal faces. Meanwhile, the homogeneity of the surface supersaturation is also improved. The crystal rotation rate strongly influences the magnitude and distribution of the prismatic surface supersaturation. As the crystal size increases from 25 cm to 35 cm, the distribution homogeneity of the prismatic surface supersaturation improves significantly, which is beneficial to crystal growth. Additionally, the importance of natural and forced convections in mass transport are discussed. Results show that the effects of natural convection adjacent to crystal faces can be ignored when stirrer rotation rate is greater than 400 rpm.

    更新日期:2020-01-17
  • Optical characterizations of Cd1-XZnXTe mixed crystals grown by vertical Bridgman-Stockbarger method
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-17
    H.P. Hsu; D.Y. Lin; C.W. Chen; Y.F. Wu; K. Strzałkowski; P. Sitarek

    Cadmium zinc telluride is a tunable band gap II–VI compound semiconductor, which has received considerable attention due to its applications such as nuclear radiation detectors and industrial process monitoring. We have studied the optical properties of the ternary compound semiconductors Cd1-xZnxTe grown by vertical Bridgman-Stockbarger method in the whole range of zinc content 0

    更新日期:2020-01-17
  • A study of in-situ etching of GaN in metalorganic chemical vapor deposition (MOCVD) by tertiarybutylchloride (TBCl)
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-17
    Bingjun Li; Sizhen Wang; Mohsen Nami; Jung Han

    This paper reports a study of the effect of NH3 flow rate and reactor temperature on the tertiarybutylchloride (TBCl) etching of patterned GaN-on-sapphire templates. It is found that a reduced NH3 flow rate and an elevated reactor temperature can eliminate islands or dots on the surface, while at the same time, enhance the etching around dislocations. TBCl etching was also performed on planar bulk GaN templates with much lower dislocation density. We find an atomically flat and layer-by-layer etching behavior within the region free of dislocations. Surface kinetics analysis reveals a short diffusion length of etching products. Room-temperature photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS) measurements confirm that TBCl etching is capable of removing the damage and impurities induced by plasma etching without introducing additional damage.

    更新日期:2020-01-17
  • Imaging of microdefects in ZnGeP2 single crystals by X-ray topography
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-14
    Zuotao Lei; Alexei Okunev; Chongqiang Zhu; Galina Verozubova; Chunghui Yang

    The contrast from microdefects in ZnGeP2 crystals is studied. Simulation of images in X-ray topography based on the Borrmann effect is carried out for a model of a coherent inclusion of spherical form in an infinite isotropic matrix. For this simulation, a semi-phenomenological theory of contrast from defects with a slowly changing deformation field is applied. It is shown that the contrast from the inclusion is a complex function, depending on the nature of defect (sign of the deformation of the matrix), the magnitude of the deformation caused by the defect, its depth in the crystal, the modulus of the diffraction vector g and the topography used (reflection or transmission). The most common images are intensity rosettes of double or triple contrast, whose lobes are elongated along the diffraction vector. These are created by inclusions, located near the X-ray exit surface of the sample. Analysis of experimental data shows that the majority of microdefects in ZnGeP2 revealed by Borrmann method (∼96%) show good agreement with proposed model. All the features of the experimental images are explained by the theory. Additionally, the contrast from dislocation loops and from groups of big inclusions which have non-Coulombic deformation fields is observed.

    更新日期:2020-01-15
  • Pharmaceutical cocrystals of nebivolol hydrochloride with enhanced solubility
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-14
    Vilas J. Nikam; Sanjay B. Patil

    Nebivolol hydrochloride is an antihypertensive BCS class II drug with low solubility and high permeability prescribed as antihypertensive. Crystal engineering was applied to prepare novel cocrystal forms of nebivolol hydrochloride with general GRAS (Generally regarded as safe) molecules. Pharmaceutical cocrystals of nebivolol hydrochloride were prepared with GRAS molecules, such as 4-hydroxybenzoic acid and nicotinamide (NA), with different ratios like 1:1, 1:2, 1:3. Liquid assisted grinding and solvent evaporation method was used to prepare nebivolol hydrochloride cocrystals. All prepared crystalline forms were characterized by X-ray diffraction, differential scanning calorimetry, and FT-IR to confirm their purity and formation of cocrystals. X-ray crystal data provided details of hydrogen bonding and interactions between drug and co-formers and differential scanning calorimetry provided changes in thermal behaviour and formation of cocrystals. Physicochemical properties such as solubility and dissolution rate were measured and found that all the co-crystals dissolved faster and their equilibrium solubility is higher than the parent drug. Nebivolol hydrochloride - 4 - hydroxy benzoic acid cocrystals showed highest solubility among all crystalline forms.

    更新日期:2020-01-15
  • Manufacture and Characterization of Two Distinct Quasi-polymorphs of Empagliflozin
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-14
    Paul Kim; Ga-Young Kim; Min-Yong Cho; Min-Jeong Lee; Guang J. Choi

    We investigated the polymorphic behaviors of empagliflozin (EMP), an SGLT2 inhibitor focusing on the preparation and characterization of its two distinct quasi-polymorphs combined with in-line monitoring of crystallization processes. EMP has only been reported as a single polymorph without pseudo-polymorphs so far. In this study, two differentiable crystal forms, the needle-shaped ‘Form I’ and platy-shaped ‘Form P’, were reproducibly created using an anti-solvent approach. Although the two forms of EMP yielded the same results in many of these analyses, they could be differentiated by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), and microscopy. Based on a detailed analysis of DSC thermograms, a small but obvious transition was detected during the melting of crystalline EMP at 152∼157°C. This transition, which occurred at a low activation energy, was identified as a polymorphic transformation from Form P to Form I. The anti-solvent crystallization process was monitored by in-line NIR absorbance measurements and interpreted using principal component analysis (PCA). The crystal form was dependent on the crystallization solvent. Two different solvent/anti-solvent pairs (ethanol-water and ethanol-hexane) yielded substantially different PCA results, indicating distinct pathways to the creation of each crystal form. Rapid nucleation and high crystal growth rate was achieved by crystallization under Scheme P, which also exhibited fluctuation in its PC score plot. This was associated with reversible polymorphic selection between the two crystal forms during the crystallization of EMP.

    更新日期:2020-01-15
  • Electric field distribution around cadmium and tellurium inclusions within CdTe-based compounds
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-12
    Aneta Wardak; Marta Witkowska-Baran; Michał Szot; Dominika Kochanowska; Bartłomiej S. Witkowski; Andrei Avdonin; Andrzej Mycielski

    We examine two kinds of volume defects in CdTe-based compounds grown from the melt: cadmium and tellurium inclusions. We have determined their chemical composition by energy-dispersive X-ray spectroscopy and their internal morphology by infrared transmission microscopy. The tellurium inclusions are spheroidal/polyhedral, while the cadmium ones appear star-like. The core size of both the tellurium and the cadmium inclusions is 5–8 μm. Cadmium inclusions cause micro cracks so that they create star-like defects the size of which is about ten times bigger than the inclusions themselves. Each pair of branches in the star-shaped defect we associate with the three easy-cleavage planes (110) of the zinc blende structure. Using Pockels imaging we have investigated how tellurium and cadmium inclusions influence the electric field distribution in CdTe compounds, which is an important issue for nuclear detectors. Only tellurium inclusions distributed along a continuous plane have an impact on the internal electric field. Neither the separated tellurium inclusions nor the separated cadmium inclusions influence the internal electric field. Crystals of (Cd,Mn)(Te,Se) have a high concentration (104–105 cm-3) of both types of inclusions. In (Cd,Mg)Te there are numerous twin boundaries decorated with tellurium inclusions. Among the studied compounds, (Cd,Mn)Te has the highest quality.

    更新日期:2020-01-13
  • Growth of GaN single crystals with high transparency by the Li-Added Na-Flux method
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-11
    Tatsuhiko Nakajima; Masayuki Imanishi; Takumi Yamada; Kosuke Murakami; Masashi Yoshimura; Yusuke Mori

    Recently, we developed a Na-flux point seed (PS) technique and fabricated a GaN crystal with an extremely low threading dislocation density (TDD). However, the crystal grown by this technique is mainly composed of the {101¯1}-plane, which easily incorporates oxygen impurities. Generally, in the Na-flux method oxygen atoms are easily incorporated at the nitrogen site because the growth is carried out in a nitrogen-poor condition. Therefore, we attempted to fabricate GaN crystals with low oxygen concentration in the flux with a high nitrogen concentration, which was achieved by adding Li into the flux. As a result, the grown GaN crystal exhibited high transparency and the oxygen concentration was the lowest value yet reported for the {101¯1}-plane.

    更新日期:2020-01-13
  • CdTe synthesis and crystal growth using the high-pressure Bridgman technique
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-09
    Tawfeeq K. Al-Hamdi; Seth W. McPherson; Santosh K. Swain; Joshah Jennings; Joel N. Duenow; X. Zheng; D.S. Albin; T. Ablekim; E. Colegrove; M. Amarasinghe; Andrew Ferguson; Wyatt K. Metzger; Csaba Szeles; Kelvin G. Lynn

    Efficient, safe and cost-effective synthesis of CdTe from elements is rather challenging in silica sealed ampoules due to the high vapor pressure of Cd. In this article, we report on the integrated synthesis and crystal growth of high-purity CdTe using the high pressure Bridgman (HPB) technique that is scalable to large volumes. The process lends itself for cost competitive industrial production of polycrystalline feedstock material for photovoltaics, sensors and electro-optic applications. Cadmium telluride (CdTe) crystals exceeding 1 kg in size were synthesized from elemental Cd and Te sources with purity comparable to state-of-the-art gamma ray detector crystals. In addition, synthesis of highly-doped CdTe feedstock for thin film photovoltaics applications demonstrating effective incorporation of group V (As, Sb) dopants was achieved at growth speeds of ∼500 mm/hr. The technique may be applicable to produce other II-VI compounds with volatile components.

    更新日期:2020-01-09
  • Thermal Stress and Local Crystallization Parameters in Single-Crystal Rods of Ni-Mn-Ga Ferromagnetic Shape Memory Alloys
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-09
    H. Behnken; S. Hemes; E. Pagounis; M. Laufenberg

    Ni-Mn-Ga single crystal material shows a strong magnetic shape memory (MSM) effect with reversible strains of up to 12%. Single crystal rods of up to 40 mm diameter are produced in Bridgman type processes. For actuator applications small sticks are cut out of the rods. The magneto-mechanical performance of these sticks depends among other parameters on their alignment with the crystal lattice. Thus, each inhomogeneity of lattice orientation within the rod reduces the achievable yield. The lattice orientation within the single crystal rods usually differs slightly between bottom and top region, and it shows local scattering due to misorientations between the growing dendrites. In the present study the macroscopic thermal stresses induced during the crystallization process are simulated. It is found that these stresses do not affect the crystal orientation. However, they may lead to shape changes of the single crystal rod.

    更新日期:2020-01-09
  • Physical Vapor Deposition of Zinc Phthalocyanine Nanostructures on Oxidized Silicon and Graphene Substrates
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-08
    T. Mirabito; B. Huet; A.L. Briseno; D.W. Snyder

    Conventional evaporation techniques for zinc phthalocyanine (ZnPc) processing have been a preferred method for the fabrication of nanostructured films. We present a new growth methodology with independent and precise control of the growth flux and substrate temperature. This provides a consistent and well controlled growth, critical for the growth mechanism studies. ZnPc nanostructures are synthesized on single layer graphene coated silicon substrates, under a wide range of growth conditions, using this new approach. The structural features of ZnPc were investigated using Scanning Electron Microscope (SEM) and compared against previous studies of metal-phthalocyanine interactions with graphitic substrates. The observations over a wide range of evaporation conditions and substrate temperatures illustrate the ability to control film structure.

    更新日期:2020-01-09
  • Influence of Supersaturation on step evolution behavior of high concentration Fe3+ poisoned KDP crystal
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-08
    Yu Li; Weidong Li; Xiaoming Zhang; Dong Wang; Shenglai Wang; Guangxia Liu

    A series of potassium dihydrogen phosphate (KDP) crystals and Fe3+ doped KDP crystals were grown by “point seed” technique at different supersaturation. The prismatic faces growth rate of KDP crystals were measured by laser polarization interference system. The surface morphology of growth steps on {100} face were comparatively researched by atomic force microscope (AFM) systematically. The results showed that the crystal growth rate increased with the rise of supersaturation. It was interesting that the growth rate of KDP crystals in Fe3+ doped solution was faster than in un-doped solution when the supersaturation exceed 6.54%. The step bunching and slope both first increased then reduced and then rise, it shaped like “N”. The average step width of steps had a trend of first decreased then increased with the rise of supersaturation. The result of inductively coupled plasma (ICP) emission shown that the Fe3+ content increased with the rise of supersaturation. The X-ray diffraction (XRD) pattern suggested that the crystal structure had not changed after doping Fe3+.

    更新日期:2020-01-09
  • Strongly reduced V pit density on InGaNOS substrate by using InGaN/GaN superlattice
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-07
    A. Dussaigne; F. Barbier; B. Samuel; A. Even; R. Templier; F. Lévy; O. Ledoux; M. Rozhavskaia; D. Sotta

    The InGaN pseudo-substrate, namely InGaNOS (InGaN On Sapphire), is used to enhance the In incorporation rate in InyGa1-yN/InxGa1-xN multiple quantum wells (MQWs) to get red emission for micro-display applications. However, the starting material for the InGaNOS fabrication is a non-optimized In0.08Ga0.92N layer grown on GaN on sapphire substrate which exhibits V shaped defects (V pits). Such V pits remain afterwards in the final InGaNOS substrate. We demonstrate here that InxGa1-xN/GaN superlattice has the potential to cover or fill the native V pits while maintaining a pseudomorphic growth. A combination of a thin GaN interlayer and an InGaN layer in a slight tensile strain state for each pair of the superlattice is necessary to achieve this goal. In addition, it is shown that the presence of GaN interlayers improves the material quality and the surface roughness. (002) X-ray diffraction rocking curve linewidth reduces to 780 arcsec compared to 3000 arcsec for the substrate. Finally, InyGa1-yN/InxGa1-xN multiple quantum wells grown on InxGa1-xN/GaN superlattice buffer layer on InGaNOS 3.205Ȧ substrate shows a central emission wavelength, measured by photoluminescence, of 624 nm at 290K with an optical internal quantum efficiency value of 6.5%.

    更新日期:2020-01-07
  • Modeling of Bulk GaN Crystal Growth from Gallium-Sodium Solution
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-07
    Andrei Vorob'ev; Alexey Kondratyev; Vladimir Kalaev; Roman Talalaev

    A modeling approach for bulk GaN growth from gallium-sodium liquid solutions is suggested. The approach combines the thermodynamic theory of non-ideal solutions with kinetics of the chemical reactions proceeding at the free surface of the solution and at the GaN growth interface. The atomic nitrogen solubility in the solution is verified using available experimental data. The N-solubility and GaN growth rate are studied as a function of the sodium fraction in the solution and the nitrogen gas pressure. Growth of laboratory-scale (< 2 cm diameter) and industrial-scale (6’’ diameter) GaN crystals is considered. The growth rate of smaller crystals is verified against the experimental data as a function of melt composition, nitrogen pressure and temperature gradient in the melt. Optimization of crucible diameter and melt depth is performed to improve the thickness uniformity of 6’’ bulk GaN crystals.

    更新日期:2020-01-07
  • Controlling nucleation during unseeded THM growth of CdZnTe crystal
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-07
    Bangzhao Hong; Song Zhang; Lili Zheng; Hui Zhang; Cheng Wang; Bo Zhao

    There are always undesired grains formed at the beginning of unseeded THM growth which deteriorate the crystal quality greatly. In this paper, several ingots with the diameter of 27mm were grown by unseeded THM to investigate the nucleation process. The growth temperature in the experiments was 750°C and the growth rate was 5mm/day. The influence of crucible bottom geometry and temperature gradient on nucleation are studied. Numerical simulations of thermal and concentration fields were also performed for the THM process to study the growth process. The simulation results show that square cavity flow's structure and parabolic wall temperature profile are the main reason for secondary nucleation in the radial direction. Dummy crystal with cold finger was introduced in order to stabilize the thermal field and modify the lateral temperature gradient. Subsequent experimental results indicate that a large longitudinal temperature gradient with small lateral temperature gradient is more favor to suppress secondary nucleation and maintain stable growth.

    更新日期:2020-01-07
  • Self-assembly of tensile-strained Ge quantum dots on InAlAs(111)A
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-07
    Kathryn E. Sautter; Christopher F. Schuck; Trent A. Garrett; Ariel E. Weltner; Kevin D. Vallejo; Dingkun Ren; Baolai Liang; Kevin A. Grossklaus; Thomas E. Vandervelde; Paul J. Simmonds

    A recently developed growth technique enables the self-assembly of defect-free quantum dots on (111) surfaces under large tensile strains. We demonstrate the use of this approach to synthesize germanium (Ge) quantum dots on In0.52Al0.48As(111)A with >3% residual tensile strain. We show that the size and areal density of the tensile-strained Ge quantum dots are readily tunable with growth conditions. We also present evidence for an unusual transition in the quantum dot growth mode from Stranski-Krastanov to Volmer-Weber as we adjust the substrate temperature. This work positions Ge quantum dots as a promising starting point for exploring the effects of tensile strain on Ge’s band structure.

    更新日期:2020-01-07
  • Modified vertical Bridgman method: Time and cost effective tool for preparation of Cs2HfCl6 single crystals
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-03
    V. Vanecek; R. Kral; J. Paterek; V. Babin; V. Jary; J. Hybler; S. Kodama; S. Kurosawa; Y. Yokota; A. Yoshikawa; M. Nikl

    Time and cost effective methods are highly desirable in research and development of new scintillators. Modern techniques like micro-pulling down (mPD) are suitable for material screening but are unfit for the growth of some crystals. These crystals must be grown by different methods that are usually very time demanding. Modification of halide mPD apparatus by custom made elements allowed us to grow cesium hafnium chloride (Cs2HfCl6) by vertical Bridgman method (VB) with significantly reduced growth time. Structural and optical properties of samples prepared from as-grown crystals were studied and compared to crystals grown by standard VB method. The X-ray diffraction confirmed the formation of cesium hafnium chloride single-phase and natural cleavage of the crystals along the (1 1 1) crystallographic plane. Photoluminescence emission, excitation, absorption, and radioluminescence spectroscopy revealed that the optical quality of the crystals grown by modified VB method was comparable to the quality of the crystals grown by standard VB method. Therefore we can use samples prepared by modified VB to estimate and optimize the performance of Cs2HfCl6 based crystals in scintillation detectors. This setup allows the time and cost-effective material screening and it is a powerful tool for the development of new halide based single crystal scintillators.

    更新日期:2020-01-04
  • In fact, L-alanine
    J. Cryst. Growth (IF 1.573) Pub Date : 2020-01-02
    Bikshandarkoil R. Srinivasan; Aram M. Petrosyan

    It is shown that two papers of Shanmuga Sundaram et al reporting on the growth of “L-alanine potassium nitrate” (LAPN) and “L-alanine sodium nitrate” (LASN) crystals are completely erroneous. In fact, only crystals of L-alanine were obtained in both cases.

    更新日期:2020-01-02
  • Advanced High-Performance Large Diameter Cs2HfCl6 (CHC) and Mixed Halides Scintillator
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-31
    R. Hawrami; E. Ariesanti; V. Buliga; L. Matei; S. Motakef; A. Burger

    This paper reports on successful growth and performance evaluation of two large diameter Cs2HfCl6 (CHC) and Cs2HfCl4Br2 (CHCB), both recently developed scintillator crystals. The discovery of Cs2HfCl6 (CHC) as a scintillator has lately generated much interest in this material and its family, which belongs to the K2PtCl6 cubic crystal structure. CHC is an intrinsic scintillator that is non-hygroscopic (slightly deliquescent, i.e., slightly moisture sensitive but does not deteriorate much when left in air), has no self-radioactivity, provides excellent energy resolution, and has excellent non-proportionality. CHC has a moderate density of 3.9 g/cm3 and an effective atomic number of 58. Reported in this paper are transparent crack-free single crystal CHC and CHCB boules of one inch in diameter, both grown using the vertical Bridgman method. Samples retrieved from the boules, sized ∅23mm × 30mm and ∅23mm × 26mm, respectively, are characterized for their optical and scintillation properties. Energy resolutions of 3.5% and 3.7% (FWHM) at 662 keV, respectively, are reported. Light yields of 23,000 ph/MeV and 20,000 ph/MeV have been calculated for the large diameter CHC and CHCB crystals, respectively. Results comparable to previously reported results for smaller crystals have been obtained. Studies on decay time, non-proportionality, as well as detector characterization are also reported.

    更新日期:2020-01-01
  • Simulation of the creation of a defect structure of dislocation-free germanium single crystals
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-31
    V.I. Talanin; I.E. Talanin; O. Matsko

    The basis for applying the model of high-temperature impurity precipitation is decay of a supersaturated solid solution of point defects near the crystallization front. A necessary condition for high-temperature precipitation is absence of recombination processes of intrinsic point defects (vacancies and intrinsic interstitial atoms, IPDs) at high temperatures. The recombination parameters for dislocation-free germanium single crystals were estimated using the terms and concepts of Voronkov's recombination-diffusion model. It was shown that at high temperatures in germanium there is a barrier against the recombination of IPDs. It is assumed that the formation of structural imperfections, as well as in silicon, proceeds through the interaction “impurity + IPD”. The possibility of applying the mathematical apparatus the diffusion model of formation of structural imperfections to the formation of a defective structure in undoped dislocation-free germanium single crystals is considered. PACS numbers: 61.72.Bb, 61.72.Ff, 61.72.Ji, 61.72.Yx, 68.70+w, 81.10.Fq A1:defects, A1:solid solutions, B1:diamond, B2:semiconducting materials

    更新日期:2019-12-31
  • Influence of the reducing agent on the formation and morphology of the bismuth telluride nanostructures by using template assisted chemical process: From nanowires to ultrathin nanotubes
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-31
    Balaji Ketharachapalli; Naveen Nischal Pillala; Raj Kishora Dash

    One-dimensional telluride based materials have recently attracted significant attention for development of the high-efficiency thermoelectric materials. Among one dimensional nanostructures, nanotubular structure has shown significant enhancement in the energy conversion efficiency due to higher reduction in the therml conductivity as compared to other one dimensional nanostructrues. Though some progress has already been establsihed to prepare nanotubes still synthesis of ultra-thin, smoother surface and stoichiometry Bi2Te3 nanotubes are still big challenges. Herein, we have reported that properly adjusting concentration of the reducing agent, different types of one-dimensional Bi2Te3 nanostructures such as nanowires to hollow nanostructures can be synthesized by using template assisted chemical process. Furthermore, ultra-thin, smoother surface and close to stoichiometry Bi2Te3 nanotubes with a diameter of about 50 nm have been obtained by properly adjusting concentration of the reducing agent. Our experimental results evidenced that concentration of the reducing agent(hydrazine hydrate) plays a crucial role(morphology controlling agent) for synthesis of different types one-dimensional nanostructures from nanowires to ultrathin smooth surface nanotubes. A possible formation mechanism has been proposed to explain formation of the different one-dimensional Bi2Te3 nanostructures and the specific role of the reducing agent based on the experimental results.

    更新日期:2019-12-31
  • Investigation of surface morphology of InAs1-x-ySbxPy epilayers grown by liquid phase epitaxy
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-31
    Hao Xie; Hongyu Lin; Qianqian Xu; Hongbo Lu; Yan Sun; Shuhong Hu; Ning Dai

    Surface morphology of InAs1-x-ySbxPy epilayers grown by liquid phase epitaxy has been studied, which has two typical patterns: crosshatch pattern and shiny uniform pattern, depending on the lattice mismatch between the epilayer and the substrate. Two kinds of micro-defects of globules and hillocks appear in the above two patterns. Although lower temperature growth can eliminate both globules and hillocks, it also brings a problem that the band gap of InAs1-x-ySbxPy alloy is not high due to the low P composition. Our study shows that globules and hillocks have no effects on the crystalline quality and compositional uniformity of InAs1-x-ySbxPy epilayers.

    更新日期:2019-12-31
  • Formation mechanism and suppression of Ga-rich streaks at macro-step edges in the growth of AlGaN on an AlN/sapphire-template
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-31
    Keita Kataoka; Tetsuo Narita; Kayo Horibuchi; Hiroaki Makino; Kengo Nagata; Yoshiki Saito

    The formation mechanism of Ga-rich streaks in the AlGaN layers formed at macro-step edges was investigated by analyzing AlGaN layers grown by metalorganic vapor phase epitaxy on AlN/sapphire-templates. Energy dispersive X-ray spectroscopy in the cross-sectional scanning transmission electron microscopy revealed that the macro-steps formed during AlN growth were maintained through the upper AlGaN layer. This can be explained by the less interaction between adjacent macro-steps due to the sufficiently smaller surface diffusion lengths of Ga and Al species than the inter-macro-step distance of submicron to a few microns. Moreover, atomic force microscopy indicated that the apparent smooth region between macro-steps involved many atomic steps and terrace width of a few ten nanometers which may be the actual scale of the diffusion lengths. At the macro-step edge, facets that are different from a c-plane are formed. The higher incorporation efficiency of Ga atoms on these facets compared with that of the c-plane likely led to the formation of Ga-rich streaks due to the less inter-surface diffusion between the facets and c-plane regions. We demonstrated AlGaN growth without Ga-rich streaks using the flattened AlN/sapphire-template by polishing; this resulted in the achievement of homogeneous emission energies in AlGaN-based quantum wells.

    更新日期:2019-12-31
  • Calorimetric and small-angle X-ray scattering studies on the memory effect in the tetra-n-butylammonium bromide semiclathrate hydrate system
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-31
    Hironobu Machida; Takeshi Sugahara; Hiroyasu Masunaga; Izumi Hirasawa

    The solution structures in the tetra-n-butylammonium bromide (TBAB) aqueous solution relate closely with the memory effect. In the present study, the behavior derived from the existence of the residual solution structures after TBAB semiclathrate hydrate (TBAB SCH) decomposition was investigated with two methods. One is a high-precision differential scanning calorimetry. The heat capacity of a TBAB aqueous solution with memory effect was slightly larger than that after the memory effect disappeared. The larger heat capacity implies the existence of solution structures. The other is a small-angle X-ray scattering (SAXS). In the first cooling process, strong scattering derived from rapid crystallization was observed at 263.6 K. In the second cooling process where the TBAB aqueous solution exhibited the memory effect, the scattering intensity gradually increased and became remarkably strong at a temperature (approximately 277 K) higher than 263.6 K. In the second cooling process, the invariant Q, which corresponds to electron density fluctuation, increased gradually until crystallization, whereas, in the first cooling process, the change of the invariant Q was quite small until crystallization. The increase of invariant Q implies the existence of 10 – 100 nm density fluctuation, which is consistent with the cluster size (10 - 20 nm) previously observed with electron microscopy in the same system.

    更新日期:2019-12-31
  • Investigation of gas bubble growth in fused silica crucibles for silicon Czochralski crystal growth
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-29
    Antje Hirsch; Matthias Trempa; Iven Kupka; Lea Schmidtner; Christian Kranert; Christian Reimann; Jochen Friedrich

    Gas bubbles in crucibles for Czochralski (Cz) silicon growth are both necessary and detrimental: In the outer, bubble-containing (BC) layer of the crucible, they are required for mechanical stability, while in the inner, bubble-free (BF) layer, bubbles can cause the release of particles from the crucible into the melt which may disrupt the single-crystalline growth. In this work, a vacuum bake-out test (VBT) procedure was set up for unused crucible parts and a microscopic characterization routine was developed to systematically investigate bubble formation and growth. Longer process time, higher temperature, and lower atmospheric pressure lead to an increased bubble growth in both, the BC and BF layer. During the VBT, no new bubbles form in the BF layer, while existing bubbles grow. The comparison to experimental data from crucibles used in an industrial Cz process indicates that VBTs can simulate this process. This allows the prediction of the gas-bubble formation in Cz crucibles using a cost-effective and less time-consuming analyzation method.

    更新日期:2019-12-29
  • Panoramic View of Particle Morphology for Growth Mechanism Exploration:A Case Study of Micron-sized Five-fold Twinned Ag Particles from Vapor Condensation
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-28
    Guiping Ji; Ailing Ji; Nipeng Lu; Zexian Cao

    Nobel metal particles of designed morphology have found many ingenious applications in fields such as catalysis, plasmonics, metamaterials, etc. A thorough investigation of influential factors that determine the particle morphology is desirable. Micron-sized Ag particles prepared by physical vapor deposition usually result from two-step growth: condensation from dense vapor followed by continual growth of the sessile particles landing on substrate. The primary particle-substrate contact may be the decisive factor in determining the particle morphology which in turn needs be precisely characterized. Here we report investigation on the growth process of five-fold twinned Ag particles towards targeted morphology by using scanning electron microscopic imaging at variable incidence angles, in conjunction with 3D modelling, so as to reveal the particle-substrate contact profile and to infer the growth mechanism. Five-fold twinned Ag particles were obtained at large yield on SiO2/Si(100), MgO(100) and LaAlO3(100) substrates. Results show that fivefold twinned Ag particles on SiO2/Si(100) substrate are usually fully developed, demonstrating higher symmetries (Ihor D5h) and acute contact angles, while on MgO(100) and LaAlO3(100) substrates the particles are usually heavily truncated with a contact characterized by also some obtuse angles. Difference in morphology occurs in the secondary growth stage where Ag atom migration along the particle-substrate interface may or may not be allowed. A set of parameters including contacting facet/contact angles and the height-edge length ratio are proposed for the morphology description of the five-fold twinned particles on support. Our work has resolved the influential factors in determining the morphology of large metal particles from physical vapor deposition where continual growth of sessile particles landing on substrate plays a pivotal role. By manipulating the particle-substrate contact and the secondary growth stage, five-fold twinned metal particles with designed morphology can be prepared for specific applications.

    更新日期:2019-12-29
  • Strain relaxation process of undoped and Si-doped semipolar AlxGa1-xN grown on (202¯1) bulk GaN substrate
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-28
    Roy B. Chung; Anand V. Sampath; Shuji Nakamura

    The strain relaxation process of undoped and Si-doped AlxGa1-xN with various compositions and thicknesses on semipolar (202¯1) bulk GaN substrate was investigated via the cathodoluminescence (CL) and high-resolution x-ray diffraction (XRD) analyses. CL analyses showed that the strain relaxation occurred through three different mechanisms. At first, the relaxation was initiated by the basal-plane (BP) misfit dislocations (MDs) along [112¯0] followed by the crack formation along [101¯4]. As the Al composition and/or thickness of AlGaN layer further increased, the crack density saturated and non-basal plane (NBP) MDs almost parallel to [101¯4] started emerging due to the prismatic slip. Observed crack spacing was 40 ∼ 60 μm at which the energy of exposing new surfaces from the cracks is higher than Peierls potential associated with the prismatic slip. By introducing Si (2.0 ∼ 6.0 × 1018 cm-3) into the film, the formation of both BP and NBP MDs could be suppressed within our growth conditions. However, Si doping was not effective in suppressing the crack formation but there was no significant change of its density either.

    更新日期:2019-12-29
  • On the thermal stability of nearly lattice-matched AlInN films grown on GaN via MOVPE
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-28
    Damir Borovac; Wei Sun; Renbo Song; Jonathan J. Wierer; Nelson Tansu

    The thermal stability of nearly lattice-matched AlInN films grown via metalorganic vapor phase epitaxy on GaN/sapphire is investigated. The structural and morphological changes of the AlInN layers, as determined by x-ray diffraction (XRD) and atomic force microscopy (AFM), are studied when systematically varying annealing times, temperatures, and ambients to gain a better understanding of the temperature limits of the AlInN films. The samples are annealed either in the growth chamber with the same conditions (gases, pressure, and flow rates) as the original growth conditions of the AlInN samples, or in the XRD under N2. In general, the surface of the AlInN changes at temperatures > 850 0C under growth and N2 conditions mostly likely due to a loss of In as determined by AFM. However, the bulk crystal structure of the AlInN remains stable up to temperatures of 950 0C to 1050 0C (depending on ambient) as determined by XRD. These findings provide a helpful guide for future experiments involving high-temperatures (790 0C – 1050 0C) for subsequent or transition layers during epitaxial growth, and for fabricating device structures employing AlInN layers.

    更新日期:2019-12-29
  • Recent progress of high temperature vapor phase epitaxy for the growth of GaN layers – Controlled coalescence of nucleation layers
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-27
    T. Schneider; M. Förste; G. Lukin; P. Fischer; M. Barchuk; C. Schimpf; E. Niederschlag; O. Pätzold; D. Rafaja; M. Stelter

    This paper describes recent developments of the high temperature vapor phase epitaxy (HTVPE) for the growth of GaN seed layers on sapphire substrates. The concept of a controlled coalescence of nucleation layers adopted from metal organic vapor phase epitaxy is used for the first time in HTVPE to reduce the density of threading dislocations of the seed layers. This concept implies a delay of coalescence by reducing the ammonia flow and increasing the admixture of hydrogen in the carrier gas. A series of nucleation and seed layers grown under different ammonia flows and hydrogen concentrations is presented. The layers are analyzed by X-ray diffraction as well as by optical and scanning electron microscopy. Microscopic investigations reveal that nucleation layers with large facetted growth islands are formed during the delayed coalescence. The measured rocking curves and estimated dislocation densities from the mosaicity model indicate a significant improvement of the crystal quality of the corresponding seed layers. The lowest dislocation densities are found to be in the range of 4 – 5 x 108 cm–2, compared with a dislocation density of about 1 x 109 cm–2 in a reference layer grown without an intentional delay of coalescence. A possible explanation is that the existence of large growth islands with extended pyramidal facets causes a preferred bunching and annihilation of dislocations.

    更新日期:2019-12-27
  • Study on synthesis of diamond by adding magnesium silicate pentahydrate in Fe-Ni-C system
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-26
    Luyao Ding; Hongan Ma; Shuai Fang; Zhiqiang Yang; Liangchao Chen; Fangbiao Wang; Xiaopeng Jia

    In this paper, diamond crystals are successfully synthesized by adding magnesium silicate pentahydrate (Mg2Si3O8·5H2O) into the Fe-Ni-C system at 5.8-6.3 GPa pressure and 1300-1420 °C temperature. Our results show that the decomposition products of Mg2Si3O8·5H2O under high temperature and high pressure have significant inhibitory effects on the nucleation and growth of diamond. Moreover, with add the amount, the temperature and pressure of synthetic diamond also gradually increased. The SEM shows that the surface defects of the crystal also increase with the increase of the add amount. The IR spectroscopy results show that the content of nitrogen decreases with the increase of the add amount of Mg2Si3O8·5H2O in the crystals. The Raman spectrum shows that the Raman peak of the crystal shifts to the right as the added amount of Mg2Si3O8·5H2O increases. The PL spectrum results show that the increase in magnesium silicate pentahydrate reduces the intensity of NV- and NV0 centers in the crystal. Therefore, our research results provide important ways for understanding the formation mechanism of natural diamond.

    更新日期:2019-12-27
  • SYNTHESIS OF ZINC BORATE USING WATER SOLUBLE ADDITIVES: KINETICS AND PRODUCT CHARACTERIZATION
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-24
    Gaye Ö. Çakal; Berk Baltacı; Göknur Bayram; Saim Özkar; Inci Eroglu

    Zinc borate was synthesized from the reaction of zinc oxide and boric acid in the absence or presence of seven different water soluble additives. Additive concentration and zinc oxide particle size were varied to investigate their effect on the growth kinetics of zinc borate particles. Zinc borate particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Samples taken from the reaction mixture during the synthesis were analyzed for determining the concentration of zinc oxide, boron oxide, and zinc borate. The results reveal the formation of zinc borate with the molecular formula 2ZnO·3B2O3·3H2O in the form of irregular platelets. The product retains its hydrate up to 300°C. The reaction rate was found to increase when additives or nanosize zinc oxide were used. However, a lag time is observed in the presence of additives while the reaction completion time remains unaffected. The experimental kinetics data were fit to the logistic model. The variation of the model parameters with experimental conditions was also investigated. The results reveal that the specific reaction rate increases with the increasing concentration of additives and the decreasing size of zinc oxide particles.

    更新日期:2019-12-25
  • Fabrication of a 1.5-inch freestanding GaN substrate by selective dissolution of sapphire using Li after the Na-flux growth
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-24
    Takumi Yamada; Masayuki Imanishi; Kosuke Murakami; Kosuke Nakamura; Masashi Yoshimura; Yusuke Mori

    Reducing the thermal stress induced in GaN crystals is key for the fabrication of large-diameter GaN crystals. In the Na-flux method, thermal stress is eliminated by sapphire dissolution at growth temperature after growth. We succeeded in fabricating a freestanding GaN substrate with this technique. However, the flux with Li used as a solvent to dissolve the sapphire can also dissolve the GaN. In this study, we demonstrate that increasing the amount of nitrogen can suppress GaN dissolution in the Li-added flux, without interfering in the dissolution of sapphire. This means that the sapphire and GaN have different dissolution mechanisms. By utilizing the different mechanisms, we succeeded in selectively dissolving sapphire and fabricating a 1.5-inch freestanding GaN substrate. It is revealed by secondary ion mass spectrometry (SIMS) that Li is incorporated in the crystal. The distribution of Li indicated that it was included in the crystal during sapphire dissolution.

    更新日期:2019-12-25
  • Growth of GaAs on Single-Crystal Layered-2D Bi2Se3
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-23
    W.E. McMahon; C.L. Melamed; A.E. Tamboli; E.S. Toberer; A.G. Norman

    This work demonstrates the successful growth of cubic GaAs (111) on single-crystal 2D layered Bi2Se3 (0001) substrates achieved using a cubic ZnSe buffer layer. This growth sequence was chosen based upon observed reactions between Bi2Se3 (0001) substrates and both Ga and Zn. For the conditions used in our MOCVD reactor, triethylgallium (TEGa) interacts strongly with Bi2Se3 to form Ga2Se3, which can disrupt the nucleation and growth of GaAs. Therefore, a buffer layer is needed which prevents Ga–Bi2Se3 interactions while simultaneously providing a suitable growth surface for GaAs. ZnSe was chosen because it is lattice-matched to GaAs, and can be created by annealing the Bi2Se3 under a diethylzinc (DEZn) flux. A sample utilizing this growth sequence has been grown, characterized and exfoliated as a possible pathway toward reducing the substrate cost for III-V devices such as solar cells.

    更新日期:2019-12-23
  • Correlation between open-circuit voltages and preferential glide planes of misfit dislocations of metamorphic InGaAs single junction solar cells grown on GaAs
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-23
    Akio Ogura; Hidetoshi Suzuki; Mitsuru Imaizumi

    Metamorphic growth of light absorber layers of solar cells introduces misfit dislocations due to strain relaxation, and their influences on the solar cell performance need to be characterized. In this work, we correlate the asymmetry of relaxation probabilities via different glide planes (which results in a tilt of the epilayer) with the open-circuit voltages (Voc) of several metamorphic InGaAs single junction solar cells. The devices contain graded InGaP buffer layers and are grown on a GaAs 001 wafer with a small miscut towards the 100 direction. We observe an inhomogeneous distribution of the solar cells’ Voc within the wafer and are able to correlate the Voc fluctuation to a difference in the asymmetry of the glide plane distributions of α and β dislocations. In the case of solar cells exhibiting a high Voc, the glide planes of both α and β dislocations are controlled by the surface orientation. In the case of low-Voc samples, the glide planes of the β dislocations are controlled by the ordering of InGaP, while those of the α dislocations are still controlled by the surface orientation.

    更新日期:2019-12-23
  • Development of SnS nanocrystals and tuning of parameters for use as spectral selective photoabsorbers
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-23
    Arun Banotra; Naresh Padha

    SnS nanocrystals have been grown using solution method from vigorously stirred solution on filtration (S1) and direct solidification under constant temperature (S2). The work demonstrates comparison in terms of structure, optical, composition and morphology for the determination of nanocrystal characteristics. Both the synthesised samples possess herzenbergite orthorhombic SnS phase with crystallinity ∼ 31 and 69 nm determined from X-ray diffraction data. The structural results exhibit changes in most significant peak (MSP), lattice parameters, volume, axis strain, dislocation density and number of crystallites in the form of a deformed nanostructure due to the presence of inorganic-organic hybrid. The changes in optical parameters corroborated well with the PL results and exhibit high photosensitive character. Morphology and composition of the synthesised nanocrystals have also found in aggregate to structural and optical results. Besides this, FTIR spectrum exhibit strong and weak SnS characteristic peaks alongwith OH and H-O-H vibrations. In summary, synthesised SnS nanocrystals possess sharp transition with high photo absorption that can be employed significantly for various photonic applications.

    更新日期:2019-12-23
  • How the intermediate stage of a phase transition process transforms to the concluding stage of Ostwald ripening
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-23
    I.V. Alexandrova; A.A. Ivanov; D.V. Alexandrov

    A theoretical description of the intermediate stage of the phase transformation process, passing into the Ostwald ripening stage, is presented. First, we consider the intermediate stage of nucleation and growth of crystals in the supercooled melts or supersaturated solutions with allowance for fluctuations in their growth rates. The evolutionary behavior of the particle-size distribution function and the metastability degree is described analytically for the Meirs kinetic mechanism. The asymptotic solution for the “tail” of the particle-size distribution function is deduced in the form of the power-dependent function. This distribution function is used as the initial condition for the concluding stage where Ostwald ripening occurs. On this basis, the concluding stage of Ostwald ripening is analytically described. Namely, the maximum of the distribution function is lower and shifted to the left in comparison with the Lifshitz-Slyozov (LS) asymptotic solution. In addition, the distribution function obtained has a “tail” on the right of the LS blocking point. The theory is in good agreement with experimental data.

    更新日期:2019-12-23
  • Characterization of Defects and Strain in the (AlxGa(1-x))0.5In0.5P/ GaAs System by Synchrotron X-ray Topography
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-23
    Hongyu Peng; Tuerxun Ailihumaer; Yafei Liu; Balaji Raghothamachar; Michael Dudley

    Synchrotron white beam X-ray topography and monochromatic beam topography have been applied to study GaAs substrates and (AlxGa(1-x))0.5In0.5P epitaxial layers grown on them that are being developed for LEDs. The GaAs substrates are 15° offcut toward [110] and mainly consist of dislocations in the {111} slip planes and low angle grain boundaries. The nominally lattice matched (AlxGa(1-x))0.5In0.5P layers contain defects such as threading dislocations replicated from the substrates, inclusions and misfit dislocations generated during organometallic vapor phase epitaxy (OMVPE) growth. The existence of misfit dislocations (MDs) indicates that strain relaxation has taken place to accommodate the in-plane lattice mismatch between epitaxial layer and substrate. The driving force for the glide of threading dislocations and relaxation efficiency of dislocations with different Burgers vectors and glide planes has been analyzed in the wafers with 15° offcut to predict the Burgers vectors and line directions of dislocations that dominate strain relaxation. Burgers vectors have been determined using ray tracing simulations. Reciprocal space maps (RSMs) recorded from the wafers to measure the strain and tilt of the epilayers show both in-plane and out-of-plane lattice mismatch as well as tilt between epilayer and substrate. A modified Nagai’s model has been developed to analyze and account for in-plane and out-of-plane tilt.

    更新日期:2019-12-23
  • Bayesian Optimization for a High- and Uniform-Crystal Growth Rate in the Top-Seeded Solution Growth Process of Silicon Carbide under Applied Magnetic Field and Seed Rotation
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-23
    Yuto Takehara; Atsushi Sekimoto; Yasunori Okano; Toru Ujihara; Sadik Dost

    The Top-Seeded Solution Growth (TSSG) method is a promising technique for the production of high-quality SiC single crystal. To achieve a high- and uniform-growth rate in the TSSG process of SiC, the fluid flows developing in the growth solution (melt), due to the applied and induced electromagnetic fields, buoyancy, seed rotation ,and free surface tension gradient, need to be controlled. Previous numerical analysis has shown that such complex flows in the TSSG melt can be controlled by the applications of a static magnetic field and seed rotation. However, the requirement of significant computational resources prevented us from carrying out the needed optimization for the process parameters involved. In order to resolve the computational demand issue, in this study, we utilized the Bayesian optimization algorithm for an efficient optimization of the associated control parameters of the TSSG process of SiC. It was shown that the Bayesian algorithm determines the optimal state at about roughly 1/4 of the computational cost of a conventional optimization, and accurately predicts the growth-rate evaluation function around the optimal state. The optimal state obtained by the present optimization process predicts a high- and uniform-growth rate in the TSSG system of SiC considered in this work.

    更新日期:2019-12-23
  • Pre-nucleation and particle attachment of bismuth tri-iodide onto graphene substrates
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-21
    L. Fornaro; D. Ferreira; H. Bentos Pereira; A. Olivera

    BiI3 nucleation was performed by physical vapor transport (PVT) onto graphene covered TEM grids and graphene covered SiO2 substrates. Depositions were characterized by High Resolution Transmission Electron Microscopy (HR-TEM) and by Scanning Electron Microscopy with Field Emission Gun (SEM-FEG). Amorphous entities 2-3 nm in size were observed. They continue to be present even under the TEM beam and suffer rapid transformations between ordered and disordered structures. Given their size and amorphous character, we conclude that they are pre-nucleation entities, similar to the ones observed in solution and chemical vapor deposition (CVD) systems in the reports of non-classical nucleation research. The oriented attachment and amorphous addition of entities about 2-3 nm in size, giving larger ones of about 10-20 nm was observed. Nanoparticles interact among them by these non-classical mechanisms giving stable and oriented crystalline structures, in agreement with the different pathways reported in non-classical nucleation investigations. Platelets up to about 100-200 nm in size were also obtained, similar when imaged by TEM and by SEM. They give TEM clear Moirè diagrams, similar to the ones obtained for other van der Waals superstructures. Non-classical nucleation here reported is similar to the one obtained for bismuth tri-iodide onto amorphous substrates, although the post growth - dictated by the crystalline substrate- is different, and gives van der Waals heterostructures. Results may be a valuable contribution to the development of a general theory for non-classical nucleation mechanisms in all kind of systems, and, as well, of 2D van der Waals materials and their applications.

    更新日期:2019-12-21
  • Effect of Different Substrates on Si and Ta co-doped Ga2O3 Films Prepared by Pulsed Laser Deposition
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-21
    Tao Zheng; Wei He; Liyun Wang; Jingbo Li; Shuwen Zheng

    In this study, the structure, morphology, electrical and optical properties of Si and Ta co-doped gallium oxide (Ga2O3) films deposited on (100) Ga2O3, (0001) sapphire and quartz substrates by pulsed laser deposition are analyzed. The Si and Ta co-doped Ga2O3 film on Ga2O3 substrate possessed the best crystal quality with a high carrier concentration of 1.12×1020 cm-3 and a conductivity of 2.13 S·cm-1 compared to the sapphire and quartz substrates. The Si and Ta co-doped Ga2O3 films on different substrates exhibited high transmittance (>73%) above 300 nm and smooth film surface. The optical gap of Si and Ta co-doped Ga2O3 films on Ga2O3, sapphire and quartz substrates decreases from 4.89 to 4.85 eV, and the corresponding Urbach energy increases from 0.396 to 0.704eV, so the homoepitaxial Si and Ta co-doped Ga2O3 film possess the best quality.

    更新日期:2019-12-21
  • Surface-orientation Control of Silicon Thin Films via Aluminum-induced Crystallization on Monocrystalline Cubic Substrates
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-20
    Mel Hainey; Eddie (Chenhui) Zhou; Loic Viguerie; Noritaka Usami

    Silicon thin films with uniform Si(111) surface orientation (>95%) have been fabricated on amorphous substrates through aluminum-induced crystallization. However, Si(100) oriented films have not been fabricated with nearly the same degree of uniformity. For Al and Si thicknesses below 50nm, Si nucleation has been previously proposed to initiate at the Al/substrate interface, suggesting that a cubic (100) oriented substrate could promote highly uniform Si(100) oriented thin film fabrication. Using two single crystalline (100) oriented substrates, strontium titanate and germanium, we demonstrate how substrate surface orientation and surface termination affect the crystallization and preferential orientation of silicon thin films fabricated by aluminum-induced crystallization.

    更新日期:2019-12-21
  • Growth and properties of Centimeter-sized lead free all inorganic perovskite Cs2AgBiBr6 crystal by additive CH3COONa
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-19
    Wenqian Zhang; Hebing Zhu; Shangke Pan; Haiyan Li; Jianyu Zhang; Zheng Gong; Yan Zhang; Jianguo Pan

    Cs2AgBiBr6 is a very promising lead-free double perovskite semiconductor material for low limit x-ray detection. However, the limited size of only 3 ∼ 4 mm single crystals have been reported using inverse temperature crystallization method recently. To grow larger single crystals of Cs2AgBiBr6, only one, two or three single crystals should be grown during the spontaneous crystallization process. We have found that additive CH3COONa can solve this problem of the numbers of as-grown crystals. Single crystal Cs2AgBiBr6 with the maximum size of 13 mm has been successfully grown by cooling the solution with additive 30% CH3COONa. The Powder X-ray diffraction pattern of (111) plane revealed that the as-grown crystal had a good single crystallinity. Based on the single crystal, the optical transmission spectra, optical transmission microscopy image, temperature dependent photon-emission spectra and current-voltage properties have also been investigated. Therefore, CH3COONa is a suitable additive agent to grow larger Cs2AgBiBr6 single crystal with centimeter size.

    更新日期:2019-12-20
  • A phase-field study of lamellar eutectic growth with solid-solid boundary anisotropy
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-18
    Tu Zhixin; Zhou Jianxin; Tong Lele; Guo Zhao

    The lamellar growth with solid-solid boundary anisotropy during directional solidification is studied by phase-field method. An anisotropy function with forbidden orientation is adopted. The influence of anisotropy on steady and unsteady lamellar morphology is analyzed. For the steady patterns, the locked and floating lamellae can be distinguished under current anisotropy function. The curve of tilted angle versus rotation angle of crystallographic orientation can be divided into a locked branch, a floating branch, and a “discontinuous angle jump” between the two branches in the simulation results. Because the locked lamellae have smaller contact angles, the growth undercooling of locked lamellae is smaller than that of floating lamellae. As rotation angle and lamellar spacing vary, the unsteady lamellar morphology exhibits three types of oscillations: floating oscillation, locked oscillation and mixed oscillation. Both rotation angle and lamellar spacing are the inducer of mixed oscillation. With the increase of lamellar spacing, the amplitude of oscillation increases regardless of the type of oscillation. Furthermore, a lamellar morphology transition map is obtained which gives a detailed exhibition of the influence of rotation angle and lamellar spacing.

    更新日期:2019-12-19
  • Floating zone furnace equipped with a high power laser of 1kW composed of five smart beams
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-17
    Yoshio Kaneko; Yoshinori Tokura

    A floating zone furnace is a powerful tool for single crystal growth. Here, we report the floating zone furnace using a high power diode laser of 1kW composed of five 200 Watt heating beams. The five beams with the designed irradiation intensity distribution enable the melt-growth of single crystals for refractory materials having a high melting temperature above 2000°C, volatile materials and even incongruent materials. The power of five beams in the horizontal plane provides uniform intensity in the outer circumference of the raw material rods, while the vertical direction power of five beams can be made to have a bell shape irradiation intensity so as to relax residual thermal stress in the grown single crystal. The present furnace enables one to directly monitor the temperature of the hot spot of raw material and the molten zone within a 1 mm diameter. Such an in-situ monitoring function of the temperature on the molten zone greatly enhances the controllability for optimizing the crystal growth condition.

    更新日期:2019-12-18
  • Influence of the growth interface shape on the defect characteristics in the facet region of 4H-SiC single crystals
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-17
    Matthias Arzig; Michael Salamon; Ta Ching Hsiao; Norman Uhlmann; Peter J. Wellmann

    Two 75mm 4H-SiC single crystals are grown by the physical vapor transport (PVT) technique, using different insulation materials. The insulation material of higher thermal conductivity led to an increased radial temperature gradient. The evolution of the growth front was monitored using the in-situ computed tomography (CT). A slightly bent growth interface and a bigger facet are formed during the growth applying a lower radial temperature gradient while a smaller facet and steeper crystal flanks are formed in the case of the larger radial temperature gradient. Micropipes are deflected laterally by large surface steps on the steep crystal flanks and a reduction of threading edge dislocations by 60% is revealed by KOH defect etching.

    更新日期:2019-12-18
  • Al(ON) Gate Dielectrics for 4H-SiC MOS Devices
    J. Cryst. Growth (IF 1.573) Pub Date : 2019-12-17
    Jinghua Xia; Shihai Wang; Lixin Tian; Wenting Zhang; Hengyu Xu; Jun Wan; Caiping Wan; Yan Pan; Fei Yang

    The gate dielectrics for silicon carbide based MOS devices are still crucial for their performance and reliability. Conventional thermal oxides have a poor interface quality and a low dielectric constant. To mitigate the issues brought about by conventional thermal oxidation, Al(ON) based on atomic layer deposition (ALD) technique is proposed and studied in terms of interface state density and dielectric strength/reliability. To make comparison, the results of AlN and Al2O3 grown using the same ALD technique, are included as well. It is shown that by incorporating of nitrogen/AlN, Al(ON) can reduce interface state density and border trap density. In addition, its dielectric strength/reliability in terms of time-zero-dielectric breakdown (TZDB) also improves.

    更新日期:2019-12-18
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