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  • Low Threading Dislocation Density Aluminum Nitride on Silicon Carbide Through the Use of Reduced Temperature Interlayers
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-22
    Humberto M. Foronda, Feng Wu, Christian Zollner, Muhammad Esmed Alif, Burhan Saifaddin, Abdullah Almogbel, Michael Iza, Shuji Nakamura, Steven P. DenBaars, James S. Speck

    In this work, reduced threading dislocation density AlN on (0001) 6H-SiC was realized through the use of reduced temperature AlN interlayers in the metalorganic chemical vapor deposition growth. We explore the dependence of the interlayer growth temperature on the AlN crystal quality, defect density, and surface morphology. The crystal quality was characterized using omega rocking curve scans and the threading dislocation density was determined by plan view transmission electron microscopy. The growth resulted in a threading dislocation density of 7 x 108 cm-2 indicating a significant reduction in the defect density of AlN in comparison to direct growth of AlN on SiC (∼1010 cm-2). Atomic force microscopy images demonstrate a clear step-terrace morphology that is consistent with step flow growth at high temperature. Reducing the interlayer growth temperature increases the TD inclination and thus enhances TD-TD interactions. The TDD is decreased via fusion and annihilation reactions.

    更新日期:2017-11-23
  • Effect of Sb in thick InGaAsSbN layers grown by liquid phase epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-21
    V. Donchev, M. Milanova, I. Asenova, N. Shtinkov, D. Alonso-Álvarez, A. Mellor, Y. Karmakov, S. Georgiev, N. Ekins-Daukes

    Dilute nitride InGaAsSbN layers grown by low-temperature liquid phase epitaxy are studied in comparison with quaternary InGaAsN layers grown at the same growth conditions to understand the effect of Sb in the alloy. The lattice mismatch to the GaAs substrate is found to be slightly larger for the InGaAsNSb layers, which is explained by the large atomic radius of Sb. A reduction of the band gap energy with respect to InGaAsN is demonstrated by means of photoluminescence (PL), surface photovoltage (SPV) spectroscopy and tight-binding calculations. The band-gap energies determined from PL and ellipsometry measurements are in good agreement, while the SPV spectroscopy and the tight-binding calculations provide lower values. Possible reasons for these discrepancies are discussed. The PL spectra reveal localized electronic states in the band gap near the conduction band edge, which is confirmed by SPV spectroscopy. The analysis of the power dependence of the integrated PL has allowed determining the dominant radiative recombination mechanisms in the layers. The values of the refraction index in a wide spectral region are found to be higher for the Sb containing layers.

    更新日期:2017-11-22
  • Computational analysis of heat transfer, thermal stress and dislocation density during resistively Czochralski growth of germanium single crystal
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-21
    Mohammad Hossein Tavakoli, Elahe Kabiri Renani, Mohtaram Honarmandnia, Mahdi Ezheiyan

    In this paper, a set of numerical simulations of fluid flow, temperature gradient, thermal stress and dislocation density for a Czochralski setup used to grow IR optical-grade Ge single crystal have been done for different stages of the growth process. A two-dimensional steady state finite element method has been applied for all calculations. The obtained numerical results reveal that the thermal field, thermal stress and dislocation structure are mainly dependent on the crystal height, heat radiation and gas flow in the growth system.

    更新日期:2017-11-22
  • Probing Ice Growth from Vapor Phase: A Molecular Dynamics Simulation Approach
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-21
    Ali Mohandesi, d Peter G. Kusalik

    We demonstrate a molecular dynamics simulation approach that can be used to investigate ice growth from water vapor. Using this approach, we explore ice/vapor interfacial systems focusing on the behavior of the quasi-liquid layer (QLL) which forms on the ice surface near its melting point. The dependence of the QLL on temperature, ice face and the flux of gas-phase water molecules are examined. We find that the thickness of the QLL increases by increasing temperature, and that the prismatic QLL is thinner than the QLL on the basal face. Both observations are consistent with previous investigations. In addition, variation in the gas densities show that an increase in the flux of water molecules in the gas vapor phase, associated with higher growth rates, results in an increased thickness of the QLL.

    更新日期:2017-11-21
  • Characterization of High-Quality Kerfless Epitaxial Silicon for Solar Cells: Defect Sources and Impact on Minority-Carrier Lifetime
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-14
    Maulid M. Kivambe, Douglas M. Powell, Sergio Castellanos, Mallory Ann Jensen, Ashley E. Morishige, Barry Lai, Ruiying Hao, T.S. Ravi, Tonio Buonassisi

    We investigate the types and origins of structural defects in thin (<100 µm) kerfless epitaxial single crystal silicon grown on top of reorganized porous silicon layers. Although the structural defect density is low (has average defect density < 104 cm-2), localized areas with a defect density > 105 cm-2 are observed. Cross-sectional and systematic plan-view defect etching and microscopy reveals that the majority of stacking faults and dislocations originate at the interface between the porous silicon layer and the epitaxial wafer. Localised dislocation clusters are observed in regions of collapsed/deformed porous silicon and at decorated stacking faults. In localized regions of high extended defect density, increased minority-carrier recombination activity is observed. Evidence for impurity segregation to the extended defects (internal gettering), which is known to exacerbate carrier recombination is demonstrated. The impact of the defects on material performance and substrate re-use is also discussed.

    更新日期:2017-11-15
  • Hydrothermal synthesis and photoluminescent properties of hierarchical GdPO4•H2O:Ln3+ (Ln3+ = Eu3+, Ce3+, Tb3+) flower-like clusters
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-14
    Bao. Amurisana, Song. Zhiqiang, O. Haschaolu, Chen Yi, O. Tegus

    3D hierarchical GdPO4·H2O:Ln3+ (Ln3+ = Eu3+, Ce3+, Tb3+) flower clusters were successfully prepared on glass slide substrate by a simple, economical hydrothermal process with the assistance of disodium ethylenediaminetetraacetic acid (Na2H2L, where L4- = (CH2COO)2N(CH2)2N(CH2COO)24-). In this process, Na2H2L was used as both a chelating agent and a structure-director. The hierarchical flower clusters have an average diameter of 7–12 μm and are composed of well-aligned microrods. The influence of the molar ratio of Na2H2L/Gd3+ and reaction time on the morphology was systematically studied. A possible crystal growth and formation mechanism of hierarchical flower clusters is proposed based on the evolution of morphology as a function of reaction time. The self-assembled GdPO4·H2O:Ln3+ superstructures exhibit strong orange-red (Eu3+, 5D0→7F1), green (Tb3+, 5D4→7F5) and near ultraviolet emissions (Ce3+, 5d→7F5/2) under ultraviolet excitation, respectively. This study may provide a new channel for building hierarchically superstructued oxide micro/nanomaterials with optical and new properties.

    更新日期:2017-11-15
  • Numerical Simulations of Porous Medium with Different Permeablities and Positions in a Laterally-Heated Cylindrical Enclosure for Crystal Growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-14
    Hooman Enayati, Minel J. Braun, Abhilash J. Chandy

    This paper presents an investigation of flow and heat transfer in a large diameter (6.25 in) cylindrical enclosure heated laterally and containing a porous block that simulates the basket of nutrients used in a crystal growth reactor. The numerical model entails the use of a commercially available computational engine provided by ANSYS FLUENT, and based on a two-dimensional (2D) axisymmetric Reynolds-averaged Navier Stokes (RANS) equations. The porous medium is simulated using the Brinkman-extended model accounting for the Darcy and Forchheimer induced pressure drops. The porous ‘plug’ effects are analyzed as both its permeability/inertial resistance and locations in the reactor are changed on a parametric basis, while the Rayleigh number (<img height="24" border="0" style="vertical-align:bottom" width="88" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0022024817306887-si1.gif">Ra=gβΔTL3να) is kept constant at 1.98×109. Additionally, the effect of different ratios of the hot to the cold zone lengths are investigated as a part of the current effort. For all cases, the velocity and temperature distributions in the reactor are analyzed together with the flow patterns in, and around the porous block. A comprehensive discussion is provided with regard to the effects of the position of the porous block and its permeability on both the immediately adjacent, and far flows. The consequences on the temperature distribution in the enclosure, when the ratio of the length of the hot-to-cold zones is changed, are also analyzed.

    更新日期:2017-11-15
  • Ice crystal growth under the presence of krypton and methane at low temperature
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-13
    Taizo Kawauchi, Yoshitaka Yoda, Katsuyuki Fukutani

    To investigate the influence of foreign gas inclusion on the crystallization of ice, we studied the low-temperature (74 <<T << 160 K) vacuum deposition of water molecules mixed with Kr or CH4 in a wide range of H2O/gas mixing ratios (0.004<<R << 4) by means of in-situ X-ray diffraction. When H2O vapor containing either Kr or CH4 was condensed onto a cold substrate, ice Ih crystals were found to grow below 130 K in a film of amorphous solid water (ASW), whereas pure H2O gas formed only ASW below 135 K. Small to moderate concentrations (R >> 0.2) of Kr and CH4 enhance the formation of ice Ih and increase the crystal size, while at high foreign gas contents (R ⩽⩽0.2) that may develop Kr or CH4 crystals below 92 K, the crystal size and relative amount of ice decrease strongly. The maximum ice Ih crystal size in the order of 200 nm was observed with either Kr or CH4 at 92 K for R = 0.2. We propose that Kr and CH4 induce the crystallization of ice by acting as a surfactant.

    更新日期:2017-11-14
  • Ultraviolet emission from MgZnO films and ZnO/MgZnO single quantum wells grown by pulsed laser deposition
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-13
    Xu Wang, Zhengwei Chen, Congyu Hu, Katsuhiko Saito, Tooru Tanaka, Mitsuhiro Nishio, Qixin Guo

    MgZnO films and ZnO/Mg0.19Zn0.81O single quantum well (QW) structures with well layer thickness from 1 to 4 nm were directly prepared on sapphire substrates at the low substrate temperature of 400 °C by pulsed laser deposition (PLD). The photoluminescence (PL) peak of QW shifted from 3.51 to 3.33 eV at room temperature as the well thickness was increased from 2 to 4 nm. The PL peak position of QW with well thickness of 2 nm can be well explained by Varshni’s relation and the best fitting to the data were E(0) = 3.558 eV, α = 2.17×10-4 eV/K, and β = 589 K. No S-shape variation of PL peak position with temperature for this QW indicates low-temperature growth is an ideal candidate for eliminating the stain effect in ZnO QW.

    更新日期:2017-11-14
  • Cubic Boron Phosphide Epitaxy on Zirconium Diboride
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-13
    Balabalaji Padavala, H. Al Atabi, Lina Tengdelius, Jun Lu, Hans Högberg, J.H. Edgar

    Cubic boron phosphide (BP) is one of the least studied III-V compound semiconductors, in part because it is difficult to prepare in high quality form. In this study, zirconium diboride (ZrB2) was studied as a potential substrate for BP epitaxial layers, because of its advantages of a low lattice constant mismatch and high thermal stability. Two types of substrates were considered: ZrB2(0001) epitaxial films on 4H-SiC(0001) and bulk ZrB2(0001) single crystals. The optimal temperature for epitaxy on these substrates was 1100 °C; higher and lower temperatures resulted in polycrystalline films. The BP film/ZrB2 interface was abrupt as confirmed by cross-sectional transmission electron microscopy, attesting to the stability of ZrB2 under BP deposition conditions. The BP films were under compressive and tensile strain on ZrB2 and ZrB2/4H-SiC substrates, respectively, as determined by Raman spectroscopy, due to differences in the substrate/film coefficients of thermal expansion. This study suggests that with further optimization, ZrB2 can be an excellent substrate for BP epitaxial films.

    更新日期:2017-11-14
  • Optimization of the interfacial misfit array growth mode of GaSb epilayers on GaAs substrate
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-13
    D. Benyahia, Ł. Kubiszyn, K. Michalczewski, A. Kębłowski, P. Martyniuk, J. Piotrowski, A. Rogalski

    The growth of undoped GaSb epilayers on GaAs (001) substrates with 2° offcut towards <110>, by molecular beam epitaxy system (MBE) at low growth temperature is reported. The strain due to the lattice mismatch of 7.78% is relieved spontaneously at the interface by using interfacial misfit array (IMF) growth mode. Three approaches of this technique are investigated. The difference consists in the steps after the growth of GaAs buffer layer. These steps are the desorption of arsenic from the GaAs surface, and the cooling down to the growth temperature, under or without antimony flux. The X-ray analysis and the transmission electron microscopy point out that desorption of arsenic followed by the substrate temperature decreasing under no group V flux leads to the best structural and crystallographic properties in the GaSb layer. It is found that the 2 µm-thick GaSb is 99.8% relaxed, and that the strain is relieved by the formation of a periodic array of 90° pure-edge dislocations along the [110] direction with a periodicity of 5.6 nm.

    更新日期:2017-11-14
  • Crystal growth, defects, mechanical, thermal and optical properties of Tb3Sc2Al3O12 magneto-optical crystal
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-13
    Shoujun Ding, Qingli Zhang, Wenpeng Liu, Jianqiao Luo, Guihua Sun, Dunlu Sun

    Tb3Sc2Al3O12 (TSAG) magneto-optical crystal was grown successfully by the Czochralski (Cz) method. Its structure and crystalline quality were determined by the powder X-ray diffraction and X-ray rocking curve, respectively. The chemical etching method was employed to investigate its defects morphology with phosphoric acid as etchant. Based on the Vickers hardness experiment, the mechanical properties of TSAG crystal (including hardness, yield strength, fracture toughness and brittle index) were systematically estimated. The thermal properties of TSAG crystal in the temperature range of 280-500 K were obtained for the first time, which are valuable for evaluating its applications. The transmission spectrum of the as-grown crystal was measured at room temperature and the transmittance in the wavelength range of 505-1445 nm is found to be as high as 82.3%. All the obtained results will contribute significantly to exploring TSAG crystal that used in high-average-power magneto-optical systems.

    更新日期:2017-11-14
  • Crystal growth and scintillation performance of Cs2HfCl6 and Cs2HfCl4Br2
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-11
    Stephanie Lam, Christo Guguschev, Arnold Burger, Maria Hackett, Shariar Motakef

    The crystal growth and behavior of a high-performance, non-hygroscopic scintillator, Cs2HfCl6 (CHC) and its variant, Cs2HfCl4Br2 (CHCB) are presented in this work. CHC and CHCB were prepared by melt compounding of sublimed HfCl4 with CsCl and CsBr to produce material for Bridgman growth. The resulting 1 cm dia. and 1 in. dia. CHC crystals showed in certain parts evidence of CsCl as a secondary phase—a result of a non-stoichiometric (CsCl-rich) melt composition caused by the high vapor pressure of HfCl4 during compounding. This was verified using micro x-ray fluorescence spectrometry. There is also evidence of a secondary phase in CHCB, which has been presented for the first time. A clear CHC sample had a light yield and energy resolution of 30,000 ph/MeV and 3.3%, respectively, and decay components of 0.39 and 3.9 µs. A sample of CHCB with a secondary phase present in the core had a light yield and energy resolution of 18,600 ph/MeV and 4.4%, and with decay components of 0.38 and 2.0 µs for CHCB. Both crystals showed minimal moisture sensitivity.

    更新日期:2017-11-11
  • POTASSIUM-COBALT SULPHATE CRYSTAL GROWTH ASSISTED BY LOW FREQUENCY VIBRATIONS
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-11
    A. Sadovsky, I. Ermochenkov, E. Dubovenko, E Sukhanova, M. Bebyakin, V. Dubov, I. Avetissov

    Single crystals of K2Co(SO4)2·6H2O were grown from solution using the temperature reduction method enhanced by the axial low frequency vibration control technique (AVC-technique). Physical modeling of heat-mass transfer in solution under the AVC action was performed. The growth rate of the AVC grown crystal was found to be twice that of the crystal grown under natural convection conditions. Analysis of spectral characteristics (absorption and Raman spectra) as well as structural properties (dislocation density and microhardness) of the grown crystals showed the significant superiority of the AVC technique for the growth of K2Co(SO4)2·6H2O crystals.

    更新日期:2017-11-11
  • Investigation of effective annealing on CdMnTe:In crystals with different thickness for gamma-ray detectors
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-09
    Pengfei Yu, Yadong Xu, Yongren Chen, Jie Song, Yi Zhu, Meijing Zhang, Binggang Zhang, Yu Wang, Wei Li, Lijun Luan, Yuanyuan Du, Jing Ma, Jiahong Zheng, Zhuo Li, Min Bai, Hui Li, Wanqi Jie

    Radiation detectors with different thickness are needed to detect gamma rays with various energies. In this paper, a post-growth annealing method was used to improve the properties of CdMnTe:In (CMT:In) crystals with different thickness for gamma-ray detectors. The results indicated that Te inclusions in CMT:In crystals with different thickness were reduced remarkably after annealing. Both the resistivity and IR transmittance of annealed CMT:In crystals with different thickness increased obviously, which suggested that the crystal quality was improved. For the detectors fabricated by annealed CMT:In slices with 1 mm, 2 mm and 5 mm thickness, the energy resolutions were enhanced about 252%, 193% and 141%, respectively. And (μτ)e values were enhanced about 80%, 80% and 76%, respectively. The performance of the detectors was greatly improved after annealing.

    更新日期:2017-11-10
  • Reduction of oxygen concentration by heater design during Czochralski Si growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-07
    Bing Zhou, Wenliang Chen, Zhihui Li, Ruicun Yue, Guowei Liu, Xinming Huang

    Oxygen is one of the highest-concentration impurities in single crystals grown by the Czochralski (CZ) process, and seriously impairs the quality of the Si wafer. In this study, computer simulations were applied to design a new CZ system. A more appropriate thermal field was acquired by optimization of the heater structure. The simulation results showed that, compared with the conventional system, the oxygen concentration in the newly designed CZ system was reduced significantly throughout the entire CZ process because of the lower crucible wall temperature and optimized convection. To verify the simulation results, experiments were conducted on an industrial single-crystal furnace. The experimental results showed that the oxygen concentration was reduced significantly, especially at the top of the CZ-Si ingot. Specifically, the oxygen concentration was 6.19×1017 atom/cm3 at the top of the CZ-Si ingot with the newly designed CZ system, compared with 9.22×1017 atom/cm3 with the conventional system. Corresponding light-induced degradation of solar cells based on the top of crystals from the newly designed CZ system was 1.62%, a reduction of 0.64% compared with crystals from the conventional system (2.26%).

    更新日期:2017-11-10
  • Numerical Modeling Study on the Epitaxial Growth of Silicon from Dichlorosilane
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-07
    Imama Zaidi, Yeon-Ho Jang, Dong Guk Ko, Ik–Tae Im

    Computer simulations play an important role in determining the optimal design parameters for chemical vapor deposition (CVD) reactors, such as flow rates, positions of the inlet and outlet orifices, and rotational rates, etc. Reliability of the results of these simulations depends on the set of chemical reaction used to represent the process of deposition in the reactor. Aim of the present work is to validate the simple empirical reaction to model the epitaxial growth of silicon for a Dichlorosilane-H2 (DCS)-H2 system. Governing equations for continuity, momentum, energy, and reacting species are solved numerically using the finite volume method. The agreement between experimental and predicted growth rates for various DCS flow rates is shown to be satisfactory. The increase in growth rate with the increase in pressure is in accordance with the available data. Based on the validated chemical reaction model, a study was carried out to analyze the uniformity of the silicon layer thickness for two different flow rates in a planetary reactor. It was concluded that, based on the operating conditions, the uniformity of the silicon layer over the wafer is independent of the satellite rotational rate in the reactor.

    更新日期:2017-11-10
  • Exploring Growth Conditions and Eu2+ Concentration Effects for KSr2I5:Eu Scintillator Crystals II: Ø 25 mm Crystals
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-07
    L. Stand, M. Zhuravleva, J. Johnson, M. Koschan, Y. Wu, S. Donnal, K. Vaigneur, E. Lukosi, C.L. Melcher

    Europium doped potassium strontium iodide is a very promising scintillator for national security applications due to its ease of growth and excellent scintillation properties. For this work the crystal growth and scintillation properties of 1-inch diameter single crystals of KSr2I5:Eu2+ were investigated. We focused our efforts on optimizing the growth parameters required to produce one-inch diameter crystals without decreasing the previously reported fast pulling rate of 5 mm/h. Cracking was minimized by replacing the quartz ampoules with carbon coated quartz ampoules; thus, several crack free single crystals of KSI with varying Eu2+ concentrations were grown, including a Ø 1“ by 6” long boule of with 2.5% Eu.The maximum achievable performance of each crystal was measured using 0.012 cm3 specimens and the volumetric dependencies of the light yield, energy resolution and decay time were evaluated using specimens of KSI:Eu 2% with volumes ranging from 0.012 cm3 to 18 cm3. For large volumes (≥ 9 cm3), the performance was comparable to other high performing scintillators, with light yields up to 78,200 ph/MeV and energy resolutions as good as 3.2% at 662 keV. The initial version of a hermetic package has been developed, and the stability of the sealed crystal is promising.

    更新日期:2017-11-10
  • Crystal growth, physical properties and computational insights of semi-organic non-linear optical crystal diphenylguanidinium perchlorate grown by conventional solvent evaporation method
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-06
    M.S. Kajamuhideen, K. Sethuraman, K. Ramamurthi, P. Ramasamy

    A splendid nonlinear optical single crystals diphenylguanidinium perchlorate (DPGP) was lucratively grown by low cost solvent evaporation method with the dimensions of 8 x 4 x 2 mm3. Structural and morphological studies of grown crystal were confirmed using X-ray diffraction studies. The presence of diverse functional groups was identified using FTIR and RAMAN studies. The molecular structure of a grown crystal was inveterate by NMR studies. The optical transmittance of DPGP crystal was analyzed using UV-vis-NIR studies. Photoluminescence spectrum shows sharp, well defined emission peak at 388nm. Thermal studies assign that adduct is stable with the melting point of 164 °C. Microhardness studies declare that DPGP crystal belongs to the soft material class and their yield strength and elastic stiffness constant values were evaluated. Photoconductivity studies revealed the negative photoconductive nature of DPGP crystal. Second harmonic generation (SHG) efficiency of the DPGP crystal was 1.4 times that of potassium dihydrogen phosphate. Etching studies were carried out for different etching time. The dielectric studies were performed at different frequency. Laser damage threshold properties of DPGP crystal were examined using Nd:YAG laser system. The HOMO-LUMO energy gap evident the charge transfer interaction of the molecule. The calculated first order hyperpolarizability value is 5 times greater than that of urea. Thus, the grown DPGP single crystals are well suited for NLO device fabrications.

    更新日期:2017-11-10
  • Solid state single crystal growth of three-dimensional faceted LaFeAsO crystals
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-04
    Rhea Kappenberger, Saicharan Aswartham, Francesco Scaravaggi, Christian G.F. Blum, Mihai I. Sturza, Anja U.B. Wolter, Sabine Wurmehl, Bernd Büchner

    Solid state single crystal growth (SSCG) is a crystal growth technique where crystals are grown from a polycrystalline matrix. Here, we present single crystals of the iron pnictide LaFeAsO grown via SSCG using NaAs as a liquid phase to aid crystallization. The size of the as grown crystals are up to 2 x 3 x 0.4 mm3. Typical for this method, but very uncommon for crystals of the pnictide superconductors and especially for the oxypnictides, the crystals show pronounced facets caused by considerable growth in c direction. The crystals were characterized regarding their composition, structure, magnetic, and thermodynamic properties. This sets the stage for further measurements for which single crystals are crucial such as any c axis and reciprocal space dependent measurements.

    更新日期:2017-11-10
  • Phase-pure eutectic CoFe2O4-Ba1-xSrxTiO3 composites prepared by floating zone melting
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-03
    Martin Breitenbach, Stefan G. Ebbinghaus

    Composites consisting of ferrimagnetic CoFe2O4 and ferroelectric Ba1–xSrxTiO3 were grown by the floating zone technique. The influence of Sr substitution, growth rate and atmosphere during the floating zone process were investigated. The formation of the non-ferroelectric, hexagonal modification of BaTiO3 was avoided by a slight Sr substitution of 3 mol% and the formation of BaFe12O19 was suppressed using pure nitrogen as atmosphere during the floating zone melting. These synthesis parameters led to phase-pure, but electrically conductive CoFe2O4-Ba1–xSrxTiO3 composites. A thermal treatment at 973 K in air resulted in a strong increase of the electric resistivity accompanied by a decrease of the unit-cell parameters of both components indicating the healing of oxygen defects. SEM investigations revealed a variety of different geometric structures and crack-free interfaces between both phases. The low porosities observed in the micrographs correspond with densities above 90%. Magnetoelectric (ME) measurements confirmed a coupling between the ferroic orders of both phases with a hysteresis and maximum αME of 1.3 mV Oe-1 cm-1.

    更新日期:2017-11-10
  • High growth rate GaN on 200mm silicon by Metal-Organic Vapor Phase Epitaxy for High Electron Mobility Transistors
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-03
    M. Charles, Y. Baines, A. Bavard, R. Bouveyron

    It is increasingly important to reduce the cycle time of epitaxial growth, in order to reduce the costs of device fabrication, especially for GaN based structures which typically have growth cycles of several hours. We have performed a comprehensive study using metal-organic vapor phase epitaxy (MOVPE) investigating the effects of changing GaN growth rates from 0.9 to 14.5 µm/h. Although there is no significant effect on the strain incorporated in the layers, we have seen changes in the surface morphology which can be related to the change in dislocation behaviour and surface diffusion effects. At the small scale, as seen by AFM, increased dislocation density for higher growth rates leads to increased pinning of growth terraces, resulting in more closely spaced terraces. At a larger scale of hundreds of µm observed by optical profiling, we have related the formation of grains to surface diffusion of adatoms rate using a random walk model, implying diffusion distances from 30 µm for the highest growth rates up to 100 µm for the lowest. The increased growth rate also increases the intrinsic carbon incorporation which can increase the breakdown voltage of GaN films.Despite an increased threading dislocation density, these very high growth rates of 14.5 µm/hr by MOVPE have been shown to be appealing for reducing epitaxial growth cycle times and therefore costs in High Electron Mobility Transistor (HEMT) structures.

    更新日期:2017-11-10
  • Growth of hexagonal boron nitride on sapphire substrate by pulsed-mode metalorganic vapor phase epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-31
    Xu Yang, Shugo Nitta, Kentaro Nagamatsu, Si-Young Bae, Ho-Jun Lee, Yuhuai Liu, Markus Pristovsek, Yoshio Honda, Hiroshi Amano

    Hexagonal boron nitride (h-BN) was directly grown on sapphire substrate using alternating ammonia (NH3) and triethylboron (TEB) supply (pulsed mode) in metalorganic vapor phase epitaxy. The best condition is when just enough NH3 is supplied to fully convert the TEB within one cycle. Excess NH3 caused islands on h-BN film surface while a lack of NH3 does not form h-BN at all. The epitaxial relationship between grown h-BN layer and c-plane sapphire was confirmed to be [0001] h-BN ∥ [0001] sapphire and [10–10]h-BN ∥ , , , , , , , ,  ; sapphire. It is known that, compared to AlN, BN requires higher V/III ratios for good crystallinity, which due to severe gas-phase reactions is difficult to achieve using continuous supply. Thus using pulsed mode the FWHM of the symmetric (0002) diffraction was almost halved and the growth rate was several times faster.

    更新日期:2017-11-01
  • Kinetic analysis and polymorphic phase transformation of glycine in the presence of lauric acid
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-31
    Sevgi POLAT, Perviz SAYAN

    The phase transformation of β-glycine to α-glycine in a water/ethanol media was investigated in terms of its polymorphism in pure media and in the presence of an additive. Lauric acid was used as the additive, and the experiments were conducted in three different concentrations. First, the polymorphic phase transformation was continuously monitored by in-line measuring of the ultrasonic velocity. Next, the X-Ray diffraction (XRD) technique was applied for the solid phase analysis of the crystals to confirm the polymorphic transformation of β-glycine to α-glycine. Based on the combination of scanning electron microscopy (SEM) and morphology analyses, it was found that not only the shape but also the size of the crystals obtained were significantly affected by the additive. The crystals obtained were further characterized by means of thermogravimetric analyzer, elemental analyzer and Fourier-transform infrared (FTIR) spectrometer. The attained thermal data were utilized to calculate the activation energy using various kinetic models based on the isoconversional method. The kinetic results revealed that the addition of lauric acid led to an increase of around 10% in the average activation energy of the glycine crystals during decomposition process. As suggested by the elemental and FTIR analyses conducted, this increase could be related to lauric acid adsorption on the crystal surface.

    更新日期:2017-11-01
  • Kinetics of solution crystal growth of strengite, FePO4,2H2O
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-31
    Hans E. Lundager Madsen, Christian Bender Koch

    The iron(III) phosphate strengite, FePO4,2H2O, has been precipitated at 25 °C by mixing solutions of iron alum and ammonium phosphate. The rate of crystallization has been determined by pH recording. Three stages of crystal growth kinetics could be distinguished: 1) mononuclear growth, 2) polynuclear growth and, in a few cases, 3) spiral growth (BCF mechanism). From the first two, the value of edge free energy λ = 87±1 pJ/m was found. The identity of the precipitate was verified by SEM, XRD and Mössbauer spectroscopy.

    更新日期:2017-11-01
  • Comparison of GaP Nanowires Grown from Au and Sn Vapor-Liquid-Solid Catalysts as Photoelectrode Materials
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-28
    Sudarat Lee, Wen Wen, Quintin Cheek, Stephen Maldonado

    Gallium phosphide (GaP) nanowire film electrodes have been prepared via solid sublimation of GaP powder using both gold (Au) and tin (Sn) nanoparticles as the vapor-liquid-solid (VLS) catalysts on Si(111) and GaP(111)B substrates. The resultant GaP nanowires are compared and contrasted in terms of structures and photoactivity in photoelectrochemical half cells. Raman spectra implicated a difference in the surface condition of the two types of nanowires. Complete wet etching removal of metallic VLS catalysts from the as-prepared GaP nanowires was possible with Sn catalysts but not with Au catalysts. The photoresponses of both Sn- and Au-seeded GaP nanowire films were collected and examined under 100 mW cm-2 white light illumination. Au-seeded nanowire films exhibited strong n-type characteristics when measured in nonaqueous electrolyte with ferrocene/ferricenium as the redox species while Sn-seeded nanowires showed behavior consistent with degenerate n-type doping.

    更新日期:2017-10-28
  • Digitally grown AlInAsSb for high gain separate absorption, grading, charge, and multiplication avalanche photodiodes
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-28
    Yuexi Lyu, Xi Han, Yaoyao Sun, Zhi Jiang, Chunyan Guo, Wei Xiang, Yinan Dong, Jie Cui, Yuan Yao, Dongwei Jiang, Guowei Wang, Yingqiang Xu, Zhichuan Niu

    We report on the growth of high quality GaSb-based AlInAsSb quaternary alloy by molecular beam epitaxy (MBE) to fabricate avalanche photodiodes (APDs). By means of high resolution X-ray diffraction (HRXRD) and scanning transmission electron microscope (STEM), phase separation phenomenon of AlInAsSb random alloy with naturally occurring vertical superlattice configuration was demonstrated. To overcome the tendency for phase segregation while maintaining a highly crystalline film, a digital alloy technique with migration-enhanced epitaxy growth method was employed, using a shutter sequence of AlSb, AlAs, AlSb, Sb, In, InAs, In, Sb. AlInAsSb digital alloy has proved to be reproducible and consistent with single phase, showing sharp satellite peaks on HRXRD rocking curve and smooth surface morphology under atomic force microscopy (AFM). Using optimized digital alloy, AlInAsSb separate absorption, grading, charge, and multiplication (SAGCM) APD was grown and fabricated. At room temperature, the device showed high performance with low dark current density of ∼14.1 mA/cm2 at 95% breakdown and maximum stable gain before breakdown as high as ∼200, showing the potential for further applications in optoelectronic devices.

    更新日期:2017-10-28
  • Growth of N-polar GaN by Ammonia Molecular Beam Epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-27
    M.N. Fireman, Haoran Li, Stacia Keller, Umesh K. Mishra, James S. Speck

    The homoepitaxial growth of N-polar GaN was investigated by ammonia molecular beam epitaxy. Systematic growth studies varying the V/III flux ratio and the growth temperature indicated that the strongest factor in realizing morphologically smooth films was the growth temperature; N-face films needed to be grown approximately 100 °C or greater than Ga-face films provided the same metal flux. Smooth N-face films could also be grown at temperatures only 50 °C greater than Ga-face films, albeit under reduced metal flux. Too high a growth temperature and too low a metal flux resulted in dislocation mediated pitting of the surface. The unintentional impurity incorporation of such films was also studied by secondary mass ion spectroscopy and most importantly revealed an oxygen content in the mid 1017 to the mid 1018 cm-3 range. Hall measurements confirmed that this oxygen impurity resulted in n-type films, with carrier concentrations and mobilities comparable to those of intentionally silicon doped GaN.

    更新日期:2017-10-28
  • Crystal Structure and Thermal Expansion of CsCaI3:Eu and CsSrBr3:Eu Scintillators
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-25
    Matthew Loyd, Adam Lindsey, Maulik Patel, Merry Koschan, Charles L. Melcher, Mariya Zhuravleva

    The distorted-perovskite scintillator materials CsCaI3:Eu and CsSrBr3:Eu prepared as single crystals have shown promising potential for use in radiation detection applications requiring a high light yield and excellent energy resolution. We present a study using high temperature powder X-ray diffraction experiments to examine a deleterious high temperature phase transition. High temperature phases were identified through sequential diffraction pattern Rietveld refinement in GSAS II. We report the linear coefficients of thermal expansion for both high and low temperature phases of each compound. Thermal expansion for both compositions is greatest in the [001] direction. As a result, Bridgman growth utilizing a seed oriented with the [001] along the growth direction should be used to mitigate thermal stress.

    更新日期:2017-10-25
  • Overcoming Ehrlich-Schwöbel barrier in (111)A GaAs molecular beam epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-24
    Julian Ritzmann, Rüdiger Schott, Katherine Gross, Dirk Reuter, Arne Ludwig, Andreas D.Wieck

    In this work, we first study the effect of different growth parameters on the molecular beam epitaxy (MBE) growth of GaAs layers on (111)A oriented substrates. After that we present a method for the MBE growth of atomically smooth layers by sequences of growth and annealing phases. The samples exhibit low surface roughness and good electrical properties shown by atomic force microscopy (AFM), scanning electron microscopy (SEM) and van-der-Pauw Hall measurements.

    更新日期:2017-10-24
  • Controlled growth of MoS2 nanopetals on the silicon nanowire array using the chemical vapor deposition method
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-23
    Shang-Min Chen, Yow-Jon Lin

    In order to get a physical/chemical insight into the formation of nanoscale semiconductor heterojunctions, MoS2 flakes are deposited on the silicon nanowire (SiNW) array by chemical vapor deposition (CVD). In this study, H2O2 treatment provides a favorable place where the formation of Si-O bonds on the SiNW surfaces that play important roles (i.e., the nucleation centers, catalyst control centers or “seeds”) can dominate the growth of MoS2 on the SiNWs. Using this configuration, the effect of a change in the S/MoO3 mass ratio (MS/MMoO3) on the surface morphology of MoS2 is studied. It is shown that an increase in the value of MS/MMoO3 leads to the increased nucleation rate, increasing the size of curved MoS2 nanopetals. This study provides valuable scientific information for directly CVD-grown edge-oriented MoS2/SiNWs heterojunctions for various nanoscale applications, including hydrogen evolution reaction and electronic and optoelectronic devices.

    更新日期:2017-10-24
  • Growth of AlGaN alloys under excess Group III conditions: Formation of Vertical Nanorods
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-23
    Chirantan Singha, Sayantani Sen, Pallabi Pramanik, Mainak Palit, Alakananda Das, Abhra Shankar Roy, Susanta Sen, Anirban Bhattacharyya

    Droplet Epitaxy of AlGaN nanostructures was investigated in this work. Growth was carried out by Plasma Assisted Molecular Beam Epitaxy (PA-MBE) under extreme group III rich conditions, where the excess metal remained on the growth surface and formed nanoscale metallic droplets due to the interplay of surface energy, surface diffusion and desorption, all of which are strongly dependent on the relative arrival rates of Gallium and Aluminum and the substrate temperature. Intermittent exposure of this metallic film to active nitrogen forms various types of nanostructures, whose morphology, composition and luminescence properties were evaluated. Our results indicate that for AlN, the droplet epitaxy process forms random arrays of uniform well oriented [0001] nanorods with a height of ∼1µm and a diameter of 250nm. For AlGaN grown under excess gallium, and intermittent exposure to the active plasma, structures with diameters of 200µm to 600µm and a height of 80nm were observed. We report the spontaneous formation of lateral concentric heterostructures under these conditions. A single photoluminescence (PL) peak was observed at about 260nm with a room temperature to 4K intensity ratio of ∼25%.

    更新日期:2017-10-23
  • Unveiling Polytype Transformation Assisted Growth Mechanism in Boron Carbide Nanowires
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-21
    Ningning Song, Xiaodong Li

    We demonstrate direct evidence that the lattice distortion, induced by boron carbide (BxCy) stoichiometry, assists the growth of boron carbide nanowires. The transformation between different polytypic boron carbide phases lowers the energy barrier for boron diffusion, promoting boron migration in the nanowire growth. An atomistic mass transport model has been established to explain such volume-diffusion-induced nanowire growth which cannot be explained by the conventional surface diffusion model alone. These findings significantly advance our understanding of nanowire growth processes and mass transport mechanisms and provide new guidelines for the design of nanowire-structured devices.

    更新日期:2017-10-21
  • MBE growth of few-layer 2H-MoTe2 on 3D substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-20
    Suresh Vishwanath, Aditya Sundar, Xinyu Liu, Angelica Azcatl, Edward Lochocki, Arthur R. Woll, Sergei Rouvimov, Wan Sik Hwang, Ning Lu, Xin Peng, Huai-Hsun Lien, John Weisenberger, Stephen McDonnell, Moon J. Kim, Margaret Dobrowolska, Jacek K Furdyna, Kyle Shen, Robert M. Wallace, Debdeep Jena, Huili Grace Xing

    MoTe2 is the least explored material in the Molybdenum-chalcogen family. Molecular beam epitaxy (MBE) provides an unique opportunity to tackle the small electronegativity difference between Mo and Te while growing layer by layer away from thermodynamic equilibrium. We find that for a few-layer MoTe2 grown at a moderate rate of ∼ ∼ 6 mins per monolayer, a narrow window in temperature (above Te cell temperature) and Te:Mo ratio exists, where we can obtain pure phase 2H-MoTe2. This is confirmed using reflection high-energy electron diffraction (RHEED), Raman spectroscopy and X-ray photoemission spectroscopy (XPS). For growth on CaF2, Grazing incidence X-ray diffraction (GI-XRD) reveals a grain size of ∼ ∼ 90 Å and presence of twinned grains. In this work, we hypothesis the presence of excess Te incorporation in MBE grown few layer 2H-MoTe2. For film on CaF2, it is based on > > 2 Te:Mo stoichiometry using XPS as well as ′ ′ a′ ′ and ′ ′ c′ ′ lattice spacing greater than bulk 2H-MoTe2. On GaAs, its based on observations of Te crystallite formation on film surface, 2x2 superstructure observed in RHEED and low energy electron diffraction, larger than bulk c-lattice spacing as well as the lack of electrical conductivity modulation by field effect. Finally, thermal stability and air sensitivity of MBE 2H-MoTe2 is investigated by temperature dependent XRD and XPS, respectively.

    更新日期:2017-10-21
  • Calcium phosphates recovery from digester supernatant by fast precipitation and recrystallization
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-20
    Liubov Vasenko, Haiyan Qu

    Conditional solubility of dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAp) in digester supernatant was determined as a function of pH and was compared to its conditional solubility in distilled water. Conditional solubility of both substances in digester supernatant at pH >5-6 was higher than their conditional solubility in pure water due to the presence of impurities, and this influence is more significant for HAp. Amorphous CaP was precipitated through a fast precipitation process from digester supernatant with initial total phosphate concentration 0.008 mol/L and 0.015 mol/L and Ca/P ratios 2 and 5 respectively. The amorphous CaP can be subsequently recrystallized into crystalline CaP. Obtained amorphous products have Ca/P ratio > 1, which allow performing the recrystallization process without further Ca dosing into the system. Batch recrystallization of the amorphous products resulted in crystallization of HAp, DCPD or their mixture depending on the conditions of the process. Maximum achieved P-recovery was 69.5%. The increase of phosphate concentration and the addition of seeding decreased the yield of the process but promoted crystallization of DCPD. The increase of Ca/P ratio had a positive effect on the total P-recovery. Compared with the direct batch crystallization of CaP from digester supernatant, the two-step process with fast precipitation and recrystallization significantly improved the color of the obtained products.

    更新日期:2017-10-20
  • Solution Growth and Scintillation Properties of 9-Phenylcarbazole
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-20
    Edgar V. van Loef, Gary Markosyan, Urmila Shirwadkar, Mickel McClish, Kanai S. Shah

    In this paper we report on the crystal growth and characterization of 9-phenylcarbazole (PCz). Crystals of PCz were obtained by the solution growth technique. Several organic solvents were investigated including heptane, cyclohexane, toluene, xylene, methanol, ethanol, and acetone. The largest crystals of the highest quality were grown from acetone.Radioluminescence spectra of pure PCz crystals exhibit a broad emission band peaking at 381 nm. Adding a small amount of an impurity (dopant) shifts the emission wavelength to 446 nm which is a better match to standard bialkali photomultiplier tubes. Single crystals of pure PCz have low light yields (typically < 5,000 ph/MeV), but doped crystals show high light yields of up to 25,000 ph/MeV and have a fast scintillation decay of less than 20 ns. Pulse shape discrimination with doped PCz crystals using neutron and gamma-rays from a 252Cf source yields a Figure of Merit (FOM) of about 2.7 at 1.0 MeVee cut-off energy.As far as we are aware, doped PCz is one of the brightest organic single crystal scintillators in existence and is a very promising organic neutron detector for a multitude of applications including homeland security, nuclear non-proliferation, nuclear physics, and non-destructive testing.

    更新日期:2017-10-20
  • 更新日期:2017-10-20
  • Growth of epitaxially stabilized, non-cubic Gd2O3 on silicon(111) substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-19
    M. Moellers, C. Margenfeld, T.F. Wietler, H.J. Osten

    We report on the growth of non-cubic gadolinium oxide on a silicon substrate using molecular beam epitaxy. Structural investigations with X-ray diffraction show that the structure of the oxide differs from the expected cubic structure. Possible structures of gadolinium oxide besides the only stable cubic structure include a monoclinic and a hexagonal phase. Both phases are very similar, which increases the difficulty to distinguish between the two structures. Gracing incidence X-ray diffraction results of the grown layer indicate a monoclinic structure while in contradiction to that a phi-scan shows a six-fold symmetry. We explain these results by a monoclinic structure with six rotational domains.

    更新日期:2017-10-20
  • Crystal Morphology Optimization of Thiamine Hydrochloride in Solvent System: Experimental and Molecular Dynamics Simulation Studies
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-19
    Yang Yang, Dandan Han, Shichao Du, Songgu Wu, Junbo Gong

    Thiamine hydrochloride (THCL) was produced in methanol accompanied with agglomeration in industry, the plate like morphology of THCL in methanol was not deserve to have a good quality. Selecting a suitable solvent should be considered because solvent could be one of the essential factors to impact morphology. Methanol and methanol/ethyl acetate solvent (0.2 volume fraction of methanol) was selected as the solvent system in reactive crystallization of THCL. The experiment results show the THCL crystal morphology in methanol/ethyl acetate solvent system was granular and more regular than that in methanol. In order to explicate the different crystal morphology in different solvents, molecular dynamics (MD) simulation was introduced to simulate crystal morphology in different solvents. The attachment energy (AE) model was employed to investigate the morphology of THCL under vacuum conditions, methanol and methanol/ethyl acetate solvent conditions, respectively. The simulation crystal morphology was in a good agreement with that of experimented. The particle of THCL in methanol/ethyl acetate solvent has less tendency to agglomeration, and then it is favorable to the downstream process, such as filtration, storage and transportation.

    更新日期:2017-10-20
  • Growth and Characterization of n-AlGaN 1-D Structures with Varying Al Composition using u-GaN Seeds
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-16
    San Kang, Uddipta Chatterjee, Dae-Young Um, In Seok Seo, Cheul-Ro Lee
    更新日期:2017-10-16
  • Annealing effect of the InAs dot-in-well structure grown by MBE
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-16
    Xuyi Zhao, Peng Wang, Chunfang Cao, Jinyi Yan, Fangxing Zha, Hailong Wang, Qian Gong

    We have demonstrated that in situ annealing effect has to be taken into account in order to realize the 1.31 μm InAs quantum dot lasers with the dot-in-well structure. The photoluminescence (PL) properties have been investigated for the InAs dot-in-well(DWELL) samples annealed at different temperatures in situ, simulating the annealing process during the growth of the top cladding AlGaAs layer in the laser structure. The QDs with large size in the DWELL structure are vulnerable to the annealing process at temperatures above 550 °C, revealed by the drastic change in the PL spectra. However, the DWELL structure is stable during the annealing process at 540 °C for three hours. The thermal stability of the QDs in the DWELL structure has to be considered in the growth of QD lasers for long wavelength operation.

    更新日期:2017-10-16
  • Characterization and optimization of sputtered AlN buffer layer on r-plane sapphire substrate to improve the crystalline quality of nonpolar a-plane GaN
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-13
    Daiki Jinno, Shunya Otsuki, Shogo Sugimori, Hisayoshi Daicho, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki

    Here we examined the use of AlN buffer layers of various thicknesses to improve the crystalline quality of nonpolar a-plane GaN (a-GaN) grown on an r-plane sapphire substrate. Three types of AlN buffer layers were used: sputtered AlN buffer layers (sp-AlNs) with or without annealing, and epitaxially grown AlN buffer layers (ep-AlNs). Buffer layer thicknesses of 30, 90, and 180 nm were used. We found that the surface morphological transitions with increasing thickness were different between the sp-AlNs and the ep-AlNs, and that the sp-AlNs had poorer crystallographic orientations than did the ep-AlNs. Annealing caused marked changes to occur in the surface morphologies and crystallographic orientations of the sp-AlNs; however, the positive effect of annealing was limited because the in-plane crystallographic orientation degraded with increasing layer thickness. The optimal buffer layer was found to be the 30-nm-thick annealed sp-AlN, which was composed of uniformly arranged oval grains with better crystallographic orientation than the other sp-AlNs and annealed sp-AlNs. The crystalline quality of the a-GaN epilayer grown on 30-nm-thick annealed sp-AlN had a narrower X-ray rocking curve–full width at half maximum for both the on- and off-axis planes compared with that grown on any other AlN buffer layers.

    更新日期:2017-10-14
  • Crystal growth of HVPE-GaN doped with germanium
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-12
    M. Iwinska, N. Takekawa, V.Yu. Ivanov, M. Amilusik, P. Kruszewski, R. Piotrzkowski, E. Litwin-Staszewska, B. Lucznik, M. Fijalkowski, T. Sochacki, H. Teisseyre, H. Murakami, M. Bockowski

    Crystallization by hydride vapor phase epitaxy method of gallium nitride single crystals doped with germanium and properties of the obtained material are described in this paper. Growth was performed in hydrogen and nitrogen carrier gas. The results were studied and compared. Influence of different flows of germanium tetrachloride, precursor of germanium, on the grown crystals was investigated. Ammonothermal GaN substrates were used as seeds for crystallization. Structural, electrical, and optical properties of HVPE-GaN doped with germanium are presented and discussed in detail. They were compared to properties of HVPE-GaN doped with silicon and also grown on native seeds of high quality.

    更新日期:2017-10-13
  • A comparative study of heterostructured CuO/CuWO4 nanowires and thin films
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-12
    Boris Polyakov, Alexei Kuzmin, Sergei Vlassov, Edgars Butanovs, Janis Zideluns, Jelena Butikova, Robert Kalendarev, Martins Zubkins

    A comparative study of heterostructured CuO/CuWO4 core/shell nanowires and double-layer thin films was performed through X-ray diffraction, confocal micro-Raman spectroscopy and electron (SEM and TEM) microscopies. The heterostructures were produced using a two-step process, starting from a deposition of amorphous WO3 layer on top of CuO nanowires and thin films by reactive DC magnetron sputtering and followed by annealing at 650°C in air. The second step induced a solid-state reaction between CuO and WO3 oxides through a thermal diffusion process, revealed by SEM-EDX analysis. Morphology evolution of core/shell nanowires and double-layer thin films upon heating was studied by electron (SEM and TEM) microscopies. A formation of CuWO4 phase was confirmed by X-ray diffraction and confocal micro-Raman spectroscopy.

    更新日期:2017-10-12
  • Understanding the microstructures of triangular defects in 4H-SiC Homoepitaxial
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-12
    Jianqiu Guo, Yu Yang, Balaji Raghothamachar, Taejin Kim, Michael Dudley, Jungyu Kim

    Triangular defects are frequently observed in 4H-SiC homoepitaxial layers and their existence is reported to greatly degrade the performance of corresponding p-n junction diodes. Regarding the formation mechanisms of these defects, there have been a few models postulated before, which will be briefly reviewed here. In this study, we have observed a significant number of triangular defects in a 150mm n-/n+ commercial 4H-SiC homoepitaxial wafer using Nomarski Microscopy and Synchrotron X-ray topography (SXRT). The observed defects show varying morphology and complexity. In order to investigate their complex microstructures and gain insight on the formation mechanism, selected triangular defects were characterized by high resolution transmission electron microscopy (HRTEM) and micro-Raman spectroscopy. Results confirm that all the triangular defects have a 3C-SiC nature. In addition, {111} { 111 } twins and double positioning boundaries (DPBs) were frequently observed inside the triangular defects. Based on these observations, a model has been developed to interpret the formation mechanism of these defects. In this model, the introduction of downfall particle during epitaxy creates a large triangular on-axis terrace, on which 3C-SiC crystals nucleate 2-dimensionally and grow under no constraint, eventually overgrown by 4H-SiC growth steps.

    更新日期:2017-10-12
  • Growth and Properties of Wide Bandgap (MgSe)n(ZnxCd1-xSe)m Short-period Superlattices
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-10
    Thor A. Garcia, Maria C. Tamargo

    We report the molecular beam epitaxy (MBE) growth and properties of (MgSe)n(ZnxCd1-x Se)m short-period superlattices(SPSLs) for potential application in II-VI devices grown on InP substrates. SPSL structures up to 1µm thick with effective bandgaps ranging from 2.6 eV to above 3.42 eV are grown and characterized, extending the typical range possible for the ZnxCdyMg1-x-ySe random alloy beyond 3.2eV. Additionally, ZnxCd1-xSe single and multiple quantum well structures using the SPSL barriers are also grown and investigated. The structures are characterized utilizing reflection high-energy electron diffraction, X-ray reflectance, X-ray diffraction and photoluminescence. We observed layer-by-layer growth and smoother interfaces in the QWs grown with SPSL when compared to the ZnxCdyMg1-x-ySe random alloy. The results indicate that this materials platform is a good candidate to replace the random alloy in wide bandgap device applications.

    更新日期:2017-10-10
  • Surface growth by cluster particles: Effects of diffusion and cluster’s shape
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-10
    Z. Madadi, F. Hassanibesheli, S. Esmaeili, L. Hedayatifar, A.A. Masoudi

    We use Monte Carlo simulation to study the spatiotemporal behavior of thin films generated by low kinetic energy cluster particles. To this end, two models are employed to investigate the effects of clusters’ shapes and their diffusion ability on the surface. In the first model, clusters are considered as a string of particles with unit height and non-unit length. The growth process in this model is implemented based on Random Deposition with Surface Relaxation (RDSR) model where particles can diffuse on the surface. The second model studies deposition of porous clusters with different shapes according to Random Deposition (RD) model. According to previous studies, the deposition of unit size particles based on RD model leads to a random growth. Using the RDSR model the phenomenon is observed to be under the Edward-Wilkinson universality class. Our results for both models reveal that using cluster particles with non-unit size gives rise to a porous medium which changes the universality class of models to Kardar-Parizi-Zhang (KPZ) by scaling exponents β=0.3 β = 0.3 and α=0.5 α = 0.5 .

    更新日期:2017-10-10
  • Morphological diversity of nitroguanidine crystals with enhanced mechanical performance and thermodynamic stability
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-10
    Zhilong Luo, Yingdan Cui, Weibing Dong, Qipeng Xu, Gaoxing Zou, Chao Kang, Baohong Hou, Song Chen, Junbo Gong

    Nitroguanidine (NQ) is a commonly used explosive, which has been widely used for both civilian and military explosive applications. However, the weak flowability and mechanical performance limit its application. In this work, mechanical performance and thermodynamic stability of NQ crystals were improved by controlling crystal morphologies in the crystallization process. Typical NQ crystals with multiple morphologies and single crystal form were obtained in the presence of additives during the cooling crystallization. The morphology controlled NQ crystals showed higher density, unimodal crystal size distribution and enhanced flowability. The additives showed the inhibitory effect on the nucleation of NQ crystals by in-situ FBRM and PVM determination, and the mechanism was analyzed by means of morphological prediction and molecular simulation. Furthermore, the morphology controlled NQ crystals suggested higher thermodynamic stability according to the calculation of entropy, enthalpy, Gibbs free energy and apparent activation energy on the basis of DSC results.

    更新日期:2017-10-10
  • Improvement on p-type CVD diamond semiconducting properties by fabricating thin heavily-boron-doped multi-layer clusters isolated each other in unintentionally boron-doped diamond layer
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-09
    Osamu Maida, Tomohiro Tabuchi, Toshimichi Ito

    We have developed a new fabrication process to decrease the effective activation energy of B atoms doped in diamond without a significant decrease in the carrier mobility by fabricating heavily B-doped clusters with very low mobility which are embedded in lightly-B-doped diamond layers. The resistivities of the heavily B-doped and unintentionally B-doped diamond stacked layers had almost no temperature dependence, suggesting the presence of an impurity-band conduction in these diamond layers. On the other hand, the resistivities of the samples after the embedding growth process of the stacked layers that had been appropriately divided to innumerable small clusters by means of a suitable etching process increased with decreasing the temperature from 330 to 130 K. The effective activation energies and Hall mobilities at room temperature of both samples were estimated to be 0.21 eV, 106 cm2V-1s-1 for micron-sized clusters and 0.23 eV, 470 cm2V-1s-1 for nano-sized clusters, respectively, indicating that the diamond film structure fabricated in this work is effective for the improvement of the p-type performance for the B-doped CVD diamond.

    更新日期:2017-10-09
  • Growth Study of Self-Assembled GaN Nanocolumns on Silica Glass by Plasma Assisted Molecular Beam Epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-09
    Andreas Liudi Mulyo, Yuta Konno, Julie S. Nilsen, Antonius T.J. van Helvoort, Bjørn-Ove Fimland, Helge Weman, Katsumi Kishino

    We demonstrate GaN nanocolumn growth on fused silica glass by plasma-assisted molecular beam epitaxy. The effect of the substrate temperature, Ga flux and N2 flow rate on the structural and optical properties are studied. At optimum growth conditions, GaN nanocolumns are vertically aligned and well separated with an average diameter, height and density of 72 nm, 1.2 μm and 1.6 × 109 cm-2, respectively. The nanocolumns exhibit wurtzite crystal structure with no threading dislocations, stacking faults or twinning and grow in the [0001] direction. At the interface adjacent to the glass, there is a few atom layers thick intermediate phase with ABC stacking order (zinc blende). Photoluminescence measurements evidence intense and narrow excitonic emissions, along with the absence of any defect-related zinc blende and yellow luminescence emission.

    更新日期:2017-10-09
  • Large size crystal growth and structural, thermal, optical and electrical properties of KCl1-xBrx mixed crystals
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-07
    Li Guo, Weizhao Jin, Zekun Chen, Jinghe Liu, Priya Murugasen, C.K. Mahadevan, Fanming Zeng

    Large size and high quality KCl1-xBrx mixed crystals [with x = 0.0 (pure KCl), 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0 (pure KBr)] have been grown with suitable raw material proportion by the melt (Czochralski) method using the miscible alkali halides KCl and KBr. The grown crystals have been characterized by determining their density, refractive index, lattice constant, chemical composition, thermal parameters (Debye-Waller factor, Debye temperature and Debye frequency), optical absorption, micro hardness and electrical parameters (dielectric constant, dielectric loss factor, AC, and DC electrical conductivities and AC, and DC activation energies) through X-ray diffraction, optical, mechanical and electrical (both AC and DC at various temperatures in the range 30-150 °C) measurements. Results obtained in the present study indicate that mixing KCl with KBr leads to significant tuning of thermal, optical, mechanical and electrical properties without disturbing the crystal structure. The dielectric constant is found to increase several times due to mixing and KCl0.5Br0.5 crystal has the maximum value.

    更新日期:2017-10-08
  • Temperature and emissivity measurements at the sapphire single crystal fiber growth process
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-07
    G.A. Bufetova, S.Ya. Rusanov, V.F. Seregin, Yu.N. Pyrkov, V.B. Tsvetkov

    We present a new method for evaluation the absorption coefficient of the crystal melt around the phase transition zone for the spectral range of semitransparency. The emissivity distribution across the crystallization front of the sapphire crystal fiber was measured at the quasi-stationary laser heated pedestal growth (LHPG) process  ; and the data for solid state, melt and phase transition zone (melt-solid interface) were obtained. The sapphire melt absorption coefficient was estimated to be 14 ± 2 cm-1 in the spectral range 1-1.4 μm around the melt point. It is consistent with data, obtained by different other methods. This method can be applied to determine the absorption coefficient for other materials.

    更新日期:2017-10-08
  • Synthesis of barium-strontium titanate hollow tubes using Kirkendall effect
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-06
    Xuncai Chen, Songwen Tan, SangHyuk Im, Jinsoo Kim, Woo-Sik Kim
    更新日期:2017-10-06
  • MultiferroicBiFeO3 thin films and nanodots grown on highly oriented pyrolytic graphite substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-06
    Hyun Wook Shin, Jong Yeog Son

    Multiferroic BiFeO3 (BFO) thin films and nanodots are deposited on highly oriented pyrolytic graphite (HOPG) substrates via a pulsed laser deposition technique, where the HOPG surface has a honeycomb lattice structure made of carbon atoms, similar to graphene. A graphene/BFO/HOPG capacitor exhibited multiferroic properties, namely ferroelectricity (a residual polarization of 26.8 μC/cm2) and ferromagnetism (a residual magnetization of 1.1 × 10−5 emu). The BFO thin film had high domain wall energies and demonstrated switching time of approximately 82 ns. An 8-nm BFO nanodot showed a typical piezoelectric hysteresis loop with an effective residual piezoelectric constant of approximately110 pm/V and exhibited two clearly separated current curves depending on the ferroelectric polarization direction.

    更新日期:2017-10-06
  • MBE Growth of Topological Isolators Based on Strained Semi-metallic HgCdTe Layers
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-05
    J. Grendysa, G. Tomaka, P. Sliz, C.R. Becker, M. Trzyna, R. Wojnarowska-Nowak, E. Bobko, E.M. Sheregii

    Particularities of Molecular Beam Epitaxial (MBE) technology for the growth of Topological Insulators (TI) based on the semi-metal Hg1-xCdx Hg 1 - x Cd x Te are presented. A series of strained layers grown on GaAs substrates with a composition close to the 3D Dirac point were studied. The composition of the layers was verified by means of the position of the E1 E 1 maximum in optical reflectivity in the visible region. The surface morphology was determined via atomic force and electron microscopy. Magneto-transport measurements show quantized Hall resistance curves and Shubnikov de Hass oscillations (up to 50 K). It has been demonstrated that a well-developed MBE technology enables one to grow strained Hg1-xCdx Hg 1 - x Cd x Te layers on GaAs/CdTe substrates with a well-defined composition near the 3D Dirac point and consequently allows one to produce a 3D topological Dirac semimetal - 3D analogy of graphene - for future applications.

    更新日期:2017-10-05
  • Theoretical analysis to interpret projected image data from in-situ 3-dimensional equiaxed nucleation and growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-04
    Robin P. Mooney, Shaun McFadden

    In-situ observation of crystal growth in transparent media allows us to observe solidification phase change in real-time. These systems are analogous to opaque systems such as metals. The interpretation of transient 2-dimensional area projections from 3-dimensional phase change phenomena occurring in a bulky sample is problematic due to uncertainty of impingement and hidden nucleation events; in stereology this problem is known as over-projection. This manuscript describes and demonstrates a continuous model for nucleation and growth using the well-established Johnson-Mehl-Avrami-Kolmogorov model, and provides a method to relate 3-dimensional volumetric data (nucleation events, volume fraction) to observed data in a 2-dimensional projection (nucleation count, area fraction). A parametric analysis is performed; the projection phenomenon is shown to be significant in cases where nucleation is occurring continuously with a relatively large variance. In general, area fraction on a projection plane will overestimate the volume fraction within the sample and the nuclei count recorded on the projection plane will underestimate the number of real nucleation events. The statistical framework given in this manuscript provides a methodology to deal with the differences between the observed (projected) data and the real (volumetric) measures.

    更新日期:2017-10-04
  • Towards Optimization of ACRT Schedules Applied to the Gradient Freeze Growth of Cadmium Zinc Telluride
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-03
    Mia S. Divecha, Jeffrey J. Derby

    Historically, the melt growth of II-VI crystals has benefitted by the application of the accelerated crucible rotation technique (ACRT). Here, we employ a comprehensive numerical model to assess the impact of two ACRT schedules designed for a cadmium zinc telluride growth system per the classical recommendations of Capper and co-workers. The “flow maximizing” ACRT schedule, with higher rotation, effectively mixes the solutal field in the melt but does not reduce supercooling adjacent to the growth interface. The ACRT schedule derived for stable Ekman flow, with lower rotation, proves more effective in reducing supercooling and promoting stable growth. These counterintuitive results highlight the need for more comprehensive studies on the optimization of ACRT schedules for specific growth systems and for desired growth outcomes.

    更新日期:2017-10-04
  • The effects of impurity on the stability of Horizontal Ribbon Growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-10-03
    Jiaying Ke, Aditya S. Khair, B. Erik Ydstie

    This paper quantifies the effects of different operating conditions on the stability of the crystallization interface in the horizontal ribbon growth (HRG) process. Specifically, we perform a linear stability analysis of the base state, and we derive the profiles for thermal, solutal and flow fields with regard to small-amplitude normal mode perturbations of the base state. Within the velocity boundary layer induced by the removal of solid ribbon, a linear Couette flow is assumed; at the outer edge of the boundary layer, all perturbations are assumed to dissipate. Critical operating conditions and the unstable modes have been identified. To that end, we demonstrate that fast pulling velocity (greater than 100 mm/min), low wedge factors (the ratio of the length to the thickness of the wafer is less than 500), and insufficient heat removal (temperature gradient Gl G l is less than 200 K/cm) lead to instabilities. A finite bandwidth of wavenumber for instability occurs for all the unstable modes.

    更新日期:2017-10-03
  • Solvent effects on the crystal growth structure and morphology of the pharmaceutical dirithromycin
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-30
    Yuan Wang, Zuozhong Liang

    Solvent effects on the crystal structure and morphology of pharmaceutical dirithromycin molecules were systematically investigated using both experimental crystallization and theoretical simulation. Dirithromycin is one of the new generation of macrolide antibiotics with two polymorphic forms (Form I and Form II) and many solvate forms. Herein, six solvates of the dirithromycin, including acetonitrile, acetonitrile/water, acetone, 1-propanol, N, N-dimethylformamide (DMF) and cyclohexane, were studied. Experimentally, we crystallized the dirithromycin molecules in different solvents by the solvent evaporating method and measured the crystal structures with the X-ray diffraction (XRD). We compared these crystal structures of dirithromycin solvates and analyzed the solvent property-determined structure evolution. The solvents have a strong interaction with the dirithromycin molecule due to the formation of inter-molecular interactions (such as the hydrogen bonding and close contacts (sum of vdW radii)). Theoretically, we calculated the ideal crystal habit based on the solvated structures with the attachment growth (AE) model. The predicted morphologies and aspect ratios of dirithromycin solvates agree well with the experimental results. This work could be helpful to better understand the structure and morphology evolution of solvates controlled by solvents and guide the crystallization of active pharmaceutical ingredients in the pharmaceutical industry.

    更新日期:2017-10-01
  • Facile synthesis of Co3O4 hexagonal plates by flux method
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-09-30
    Ji-Long Han, Qing-Fen Meng, Sheng-Li Gao

    Using a novel flux method, a hexagonal plate of Co3O4 was directly synthesized. In this method, CoCl2·6H2O, NaOH, and the cosolvent H3BO3 were heated to 750 °C for 2 h in a corundum crucible. The products were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscope (HRTEM). Furthermore, XRD studies indicated that the product consisted of a cubic phase of Co3O4, and the phase existed in a completely crystalline form. Then, SEM results indicated that these hexagonal plates tiered up and they had diameters in the range of 2-10 µm. According to the results of SAED and HRTEM analyses, the interlayer spacing was about 0.24 nm, which corresponds to the interlayer distance of (311) crystal plane of cubic Co3O4.

    更新日期:2017-09-30
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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