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  • Structural characterization and magnetic properties of L10-MnAl films grown on different underlayers by molecular beam epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-12
    Fumiya Takata, Toshiki Gushi, Akihito Anzai, Kaoru Toko, Takashi Suemasu

    We grow MnAl films on different underlayers by molecular beam epitaxy (MBE), and investigate their structural and magnetic properties. L10-ordered MnAl films were successfully grown both on an MgO(001) single-crystalline substrate and on an Mn4N(001) buffer layer formed on MgO(001) and SrTiO3(001) substrates. For the MgO substrate, post rapid thermal annealing (RTA) drastically improved the crystalline quality and the degree of L10-ordering, whereas no improvement in the crystallinity was achieved by altering the substrate temperature (TS) during MBE growth. However, high-quality L10-MnAl films were formed on the Mn4N buffer layer by simply varying TS. Structural analysis using X-ray diffraction showed MnAl on an MgO substrate had a cubic structure whereas MnAl on the Mn4N buffer had a tetragonal structure. This difference in crystal structure affected the magnetic properties of the MnAl films. The uniaxial magnetic anisotropy constant (Ku) was drastically improved by inserting an Mn4N buffer layer. We achieved a perpendicular magnetic anisotropy of Ku = 5.0 ± 0.7 Merg/cm3 for MnAl/Mn4N film on MgO and 6.0 ± 0.2 Merg/cm3 on STO. These results suggest that Mn4N has potential as an underlayer for L10-MnAl.

    更新日期:2018-01-12
  • Numerical simulation of 48 pairs of rods polycrystalline silicon reduction furnace
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-11
    Tang Guoqiang, Chen Cong, Cai Yifang, Zong Bing, Cai Yanguo, Wang Tihu

    With the development of the photovoltaic industry, polysilicon industrial scale Siemens CVD reactor has been expanded from 24-rod to 96-rod. In order to study the internal temperature field, the flow field and the vapor deposition reaction of the 96-rod CVD reactor, a CFD model of an industrial scale 96-rod CVD reactor was established. The numerical simulation of the flow field and temperature field in the model is carried out, and the simulated flow field and temperature field are compared with the measured value from the real CVD reactor. The error is within 5%, the model is close to the actual situation. In this paper, the influence of inlet rate on the temperature field and flow field distribution in the CVD reactor is studied.

    更新日期:2018-01-12
  • Impact of Temperature and Nitrogen Composition on the Growth of GaAsPN Alloys
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-09
    Keisuke Yamane, Shun Mugikura, Shunsuke Tanaka, Masaya Goto, Hiroto Sekiguchi, Hiroshi Okada, Akihiro Wakahara

    This paper presents the impact of temperature and nitrogen-composition on the growth mode and crystallinity of GaAsPN alloys. Reflection high-energy electron diffraction results combined with transmission electron microscopy analysis revealed that maintaining two-dimensional (2-D) growth required higher temperatures when nitrogen composition increased. Outside the 2-D growth windows, stacking faults and micro-twins were preferentially formed at {111} B planes rather than at the {111} A planes and anomalous growth was observed. The photoluminescence spectra of GaAsPN layers implies that the higher temperature growth is effective for reducing the nitrogen-related point defects.

    更新日期:2018-01-10
  • Crystal Growth and Piezoelectric Properties of Ca3Ta(Ga0.9Sc0.1)3Si2O14 Bulk Single Crystal
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-06
    Yu Igarashi, Yuui Yokota, Yuji Ohashi, Kenji Inoue, AkihiroYamaji, Yasuhiro Shoji, Kei Kamada, Shunsuke Kurosawa, Akira Yoshikawa

    Ca3Ta(Ga0.9Sc0.1)3Si2O14 langasite-type single crystal with a diameter of 1 in. was grown by Czochralski (Cz) method. Obtained crystal had good crystallinity and its lattice constants exceeded those of Ca3TaGa3Si2O14 (CTGS) according to the X-ray analysis. A crack-free specimen cut from the grown crystal was used for the measurements of dielectric constant ε11T/ ε0, electromechanical coupling factor k12, and piezoelectric constant d11. The accuracies of these measurements were better than those for the crystal grown by micro-pulling-down (μ-PD) method. Substitution of Ga with Sc resulted modification of these constants in the directions opposite to those observed after partial substitution of Ga (of CTGS) with Al. This suggests that increase of |d14| was most probably associated with enlargement of average size of the Ga sites. The crystal reported here had greater dimensions as compared to analogous crystals grown by the μ-PD method. As a result, accuracy of determination of acoustic constants of this material may be improved.

    更新日期:2018-01-06
  • Single crystals with advanced laser properties LiCaAlF6:Ce3+ grown by Bridgman technique
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-05
    A.A. Shavelev, A.S. Nizamutdinov, M.A. Marisov, I.I. Farukshin, O.A. Morozov, N.F. Rakhimov, E.V. Lukinova, S.L. Korableva, V.V. Semashko

    The aim of this work is growth of LiCaAlF6:Ce3+ (Ce:LiCAF) crystals by Bridgman technique and study of spectroscopic and laser characteristics in UV spectral range. We report on growth of LiCaAlF6:Ce3+ (1.2 at.% in the melt) crystals with refractive index inhomogeneity not worse than Δn=1.2∗10-5. The maximum absorption coefficient of Ce3+ ions appeared to be up to 7 cm-1 and maximum of slope efficiency of laser action as high as 47% in synthesized crystals was achieved.

    更新日期:2018-01-06
  • Molecular beam epitaxial growth of Zinc blende MgS on GaAs (211)B substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-05
    J. Zhu, N.M. Eldose, N. Mavridi, K.A. Prior, R.T. Moug

    This paper reports the growth of zinc blende (ZB) MgS on GaAs (211)B substrates by molecular beam epitaxy. Initial growths of (211)B ZnSe were performed at 240°C and showed to be of comparable quality to (100) ZnSe grown at the same temperature. Samples of MgS deposited on ZnSe buffers showed good quality 2D growth. Subsequently, multilayer structures of ZnSe and ZnCdSe were deposited on (211)B MgS layers for structural and optical examination before and after epitaxial lift off (ELO). Photoluminescence (PL) spectroscopy showed strong emission before and after ELO and X-ray spectra demonstrated the presence of a single continuous zinc blende phase.

    更新日期:2018-01-05
  • The Morse Code Effect: A Crystal – Crystal Transformation Observed in Gel-Grown Lead (II) Oxalate Crystals
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-04
    J.N. Lisgarten, J.A. Marks

    This paper reports on an unusual crystal–crystal transformation phenomenon, which we have called the Morse Code Effect, based on the change in appearance of lead(II) oxalate crystals grown in agarose gels.

    更新日期:2018-01-04
  • Thermodynamic Design of a High Temperature Chemical Vapor Deposition Process to Synthesize α-SiC in Si-C-H and Si-C-H-Cl Systems
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-03
    Yura Kang, Chang-Hyoung Yoo, Deok-Hui Nam, Myung-Hyun Lee, Won-Seon Seo, Suklyun Hong, Seong-Min Jeong

    In this study, we thermodynamically reviewed the suitable growth process conditions of α-SiC in the Si-C-H system using tetramethylsilane (TMS) and in the Si-C-H-Cl system using methyltrichlorosilane (MTS). In the Si-C-H-Cl system, pure solid SiC was obtained at high temperatures under a larger range of hydrogen dilution ratios than that tolerated in the Si-C-H system. X-ray diffraction and micro-Raman analysis of the products obtained at 1900, 2000, and 2100 °C showed that the α-SiC becomes more dominant with increasing temperature in the Si-C-H-Cl system. While TMS was unsuitable for high temperature processing due to its high C/Si ratio, MTS was found to be appropriate for growing α-SiC crystals at high temperatures under a range of conditions. These results indicate that a novel method to grow α-SiC single crystals through HTCVD using MTS as a precursor could be established.

    更新日期:2018-01-04
  • Visual Observation of Gas Hydrates Nucleation and Growth at a Water – Organic Liquid Interface
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-03
    Andrey S. Stoporev, Anton P. Semenov, Vladimir I. Medvedev, Artem A. Sizikov, Pavel A. Gushchin, Vladimir A. Vinokurov, Andrey Yu. Manakov

    Visual observation of nucleation sites of methane and methane-ethane-propane hydrates and their further growth in water – organic liquid – gas systems with / without surfactants was carried out. Sapphire Rocking Cell RCS6 with transparent sapphire cells was used. The experiments were conducted at the supercooling ΔTsub = 20.2°C. Decane, toluene and crude oils were used as organics. Gas hydrate nucleation occurred on water – metal – gas and water – sapphire – organic liquid three-phase contact lines. At the initial stage of growth hydrate crystals rapidly covered the water – gas or water – organics interfaces (depending on the nucleation site). Further hydrate phase accrete on cell walls (sapphire surface) and into the organics volume. At this stage, growth was accompanied by water «drawing out» from under initial hydrate film formed at water – organic interface. Apparently, it takes place due to water capillary inflow in the reaction zone. It was shown that the hydrate crystal morphology depends on the organic phase composition. In the case of water-in-decane emulsion relay hydrate crystallization was observed in the whole sample, originating most likely due to the hydrate crystal intergrowth through decane. Contacts of such crystals with adjacent water droplets result in rapid hydrate crystallization on this droplet.

    更新日期:2018-01-04
  • Nanowire growth from the viewpoint of the thin film polylayer growth theory
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-03
    Dimo Kashchiev

    The theory of polylayer growth of thin solid films is employed for description of the growth kinetics of single-crystal nanowires. Expressions are derived for the dependences of the height h and radius r of a given nanowire on time t, as well as for the h(r) dependence. These dependences are applicable immediately after the nanowire nucleation on the substrate and thus include the period during which the nucleated nanowire changes its shape from that of cap to that of column. The analysis shows that the nanowire cap-to-column shape transition is continuous and makes it possible to kinetically define the nanowire shape-transition radius by means of the nanowire radial and axial growth rates. The obtained h(t), r(t) and h(r) dependences are found to provide a good description of available experimental data for growth of self-nucleated GaN nanowires by the vapor-solid mechanism.

    更新日期:2018-01-04
  • Optimization of cooling strategy and seeding by FBRM analysis of batch crystallization
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-03
    Dejiang Zhang, Lande Liu, Shijie Xu, Shichao Du, Weibing Dong, Junbo Gong

    A method is presented for optimizing the cooling strategy and seed loading simultaneously. Focused beam reflectance measurement (FBRM) was used to determine the approximating optimal cooling profile. Using these results in conjunction with constant growth rate assumption, modified Mullin-Nyvlt trajectory could be calculated. This trajectory could suppress secondary nucleation and has the potential to control product’s polymorph distribution. Comparing with linear and two step cooling, modified Mullin-Nyvlt trajectory have a larger size distribution and a better morphology. Based on the calculating results, the optimized seed loading policy was also developed. This policy could be useful for guiding the batch crystallization process.

    更新日期:2018-01-03
  • Molecular beam epitaxial growth, transmittance and photoluminescence spectra of zinc-blende CdTe thin films with high-quality on perovskite SrTiO3 (111) substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2018-01-02
    Kun Song, Xuanting Zhu, Kai Tang, Wei Bai, Liangqing Zhu, Jing Yang, Yuanyuan Zhang, Xiaodong Tang, Junhao Chu

    High-crystalline quality CdTe thin films are grown on the largely lattice-mismatched SrTiO3 (STO) (111) substrates by molecular beam epitaxy. A transformation from a three dimensional regime to a two dimensional one is observed by the reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). The formation of an elastic deformation CdTe layer on STO (111), namely a pseudomorphic growth mode with a critical thickness of ∼40 nm, is supported by the RHEED, AFM and X-ray diffraction. Crystal structures and epitaxial relationships of CdTe epitaxial films on STO (111) are characterized by 2θ-ω scans and reciprocal space mapping. Two strong absorption peaks at the energies of ∼1.621 eV and ∼1.597 eV at 5 K are clearly observed for a ∼120 nm thick CdTe epitaxial film, which are proposed to be ascribed to the strained and unstrained epitaxial CdTe layers, respectively. Moreover, the presence of the exciton band while the absence of deep level defect states for the ∼120 nm thick CdTe film characterized by the temperature dependent photoluminescence spectra further supports the high-crystalline quality.

    更新日期:2018-01-02
  • Three Dimensional Modelling of Grain Boundary Interaction and Evolution During Directional Solidification of Multi-crystalline Silicon
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-29
    T. Jain, H.K. Lin, C.W. Lan

    The development of grain structures during directional solidification of multi-crystalline silicon (mc-Si) plays a crucial role in the materials quality for silicon solar cells. Three dimensional (3D) modelling of the grain boundary (GB) interaction and evolution based on phase fields by considering anisotropic GB energy and mobility for mc-Si is carried out for the first time to elucidate the process. The energy and mobility of GBs are allowed to depend on misorientation and the GB plane. To examine the correctness of our method, the known the coincident site lattice (CSL) combinations such as (∑a+∑b→∑a×b) ( ∑ a + ∑ b → ∑ a × b ) or (∑a+∑b→∑a/b) ( ∑ a + ∑ b → ∑ a / b ) are verified. We frther discuss how to use the GB normal to characterize a ∑3 ∑ 3 twin GB into a tilt or a twist one, and show the interaction between tilt and twist ∑3 ∑ 3 twin GBs. Two experimental scenarios are considered for comparison and the results are in good agreement with the experiments as well as the theoretical predictions.

    更新日期:2017-12-31
  • Defects subsystem and homogeneity region of ZnTe and CdTe crystals
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-27
    Ihor Horichok, Taras Parashchuk, Mariia Pylyponiuk, Oksana Soroka, Marian Voloshynovych

    Based on the comparison of theoretical calculations of the point defects formation energy by ab initio method and their concentration by the thermodynamic potentials method with the experimental data of the Hall effect study and the homogeneity region width of zinc and cadmium tellurides, it was shown that in the ZnTe crystals, as in the CdTe crystals, at the chalcogen saturation the dominant defects are cationic vacancies and antistructural chalcogen atoms, whose point symmetry corresponds to the Td group. When both zinc and cadmium tellurides are saturated with the metal, the most probable type of the dominant point defects is the electroneutral chalcogen vacancy, the formation of which is accompanied by the significant relaxation of the nearest atoms and loss of initial symmetry.

    更新日期:2017-12-27
  • Effects of withdrawal rate and starter block size on crystal orientation of a single crystal Ni-based superalloy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-27
    M. Rezaei, A. Kermanpur, F. Sadeghi

    Fabrication of single crystal (SC) Ni-based gas turbine blades with a minimum crystal misorientation has always been a challenge in gas turbine industry, due to its significant influence on high temperature mechanical properties. This paper reports an experimental investigation and numerical simulation of the SC solidification process of a Ni-based superalloy to study effects of withdrawal rate and starter block size on crystal orientation. The results show that the crystal misorientation of the sample with 40 mm starter block height is decreased with increasing withdrawal rate up to about 9 mm/min, beyond which the amount of misorientation is increased. It was found that the withdrawal rate, height of the starter block and temperature gradient are completely inter-dependent and indeed achieving a SC specimen with a minimum misorientation needs careful optimization of these process parameters. The height of starter block was found to have higher impact on crystal orientation compared to the withdrawal rate. A suitable withdrawal rate regime along with a sufficient starter block height was proposed to produce SC parts with the lowest misorientation.

    更新日期:2017-12-27
  • Effect of oxygen on dislocation multiplication in silicon crystals
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-27
    Wataru Fukushima, Hirofumi Harada, Yoshiji Miyamura, Masato Imai, Satoshi Nakano, Koichi Kakimoto

    This paper aims to clarify the effect of oxygen on dislocation multiplication in silicon single crystals grown by the Czochralski and floating zone methods using numerical analysis. The analysis is based on the Alexander–Haasen–Sumino model and involves oxygen diffusion from the bulk to the dislocation cores during the annealing process in a furnace. The results show that after the annealing process, the dislocation density in silicon single crystals decreases as a function of oxygen concentration. This decrease can be explained by considering the unlocking stress caused by interstitial oxygen atoms. When the oxygen concentration is 7.5 ×1017 cm−3, the total stress is about 2 MPa and the unlocking stress is less than 1 MPa. As the oxygen concentration increases, the unlocking stress also increases; however, the dislocation velocity decreases.

    更新日期:2017-12-27
  • Optimization of heat transfer during the directional solidification process of 1600 kg silicon feedstock
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-27
    Chieh Hu, Jyh Chen Chen, Thi Hoai Thu Nguyen, Zhi Zhong Hou, Chun Hung Chen, Yen Hao Huang, Michael Yang

    In this study, the power ratio between the top and side heaters and the moving velocity of the side insulation are designed to control the shape of the crystal-melt interface during the growth process of a 1600 kg multi-crystalline silicon ingot. The power ratio and insulation gap are adjusted to ensure solidification of the melt. To ensure that the crystal-melt interface is slightly convex in relation to the melt during the entire solidification process, the power ratio should be augmented gradually in the initial stages while being held to a constant value in the middle stages. Initially the gap between the side and the bottom insulation is kept small to reduce thermal stress inside the seed crystals. However, the growth rate will be slow in the early stages of the solidification process. Therefore, the movement of the side insulation is fast in the initial stages but slower in the middle stages. In the later stages, the side insulation gap is fixed. With these modifications, the convexity of the crystal-melt interface in relation to the melt can be maintained during the growth process with an approximately 41% reduction in the thermal stress inside the growing ingot and an 80% reduction in dislocation density along the center line of the ingot compared with the original case.

    更新日期:2017-12-27
  • Heteroepitaxial growth and interface structure of pyrochlore (Ca,Ti)2(Nb,Ti)2O7 thin films on (110) NdGaO3 substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-27
    Xiao-Wei Jin, Yue-Hua Chen, Lu Lu, Shao-Bo Mi, Lei Jin, Hong-Mei Jing, Hong Wang, Chun-Lin Jia
    更新日期:2017-12-27
  • Towards Establishing a combined rate law of Nucleation and Crystal Growth – the case study of gypsum precipitation
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-27
    Pedro M. Rendel, Ittai Gavrieli, Domenik Wolff-Boenisch, Jiwchar Ganor

    The main obstacle in the formulation of a quantitative rate-model for mineral precipitation is the absence of a rigorous method for coupling nucleation and growth processes. In order to link both processes, we conducted a series of batch experiments in which gypsum nucleation was followed by crystal growth. Experiments were carried out using various stirring methods in several batch vessels made of different materials. In the experiments, the initial supersaturation degree of the solution with respect to gypsum (Ωgyp) was set between 1.58-1.82. Under these conditions, heterogeneous nucleation is the dominant nucleation mode. Based on changes in SO42- concentration with time, the induction time of gypsum nucleation and the following rate of crystal growth were calculated for each experiment. The induction time (6-104 h) was found to be a function of the vessel material, while the rates of crystal growth, which varied over three orders of magnitude, were strongly affected by the stirring speed and its mode (i.e. rocking, shaking, magnetic stirrer, and magnetic impeller). The SO42- concentration data were then used to formulate a forward model that couples the simple rate laws for nucleation and crystal growth of gypsum into a single kinetic model. Accordingly, the obtained rate law is based on classical nucleation theory and heterogeneous crystal growth.

    更新日期:2017-12-27
  • Careful stoichiometry monitoring and doping control during the tunneling interface growth of an n+InAs(Si)/p+GaSb(Si) Esaki diode
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-26
    S. El Kazzi, A. Alian, B. Hsu, A.S. Verhulst, A. Walke, P. Favia, B. Douhard, W. Lu, J.A. del Alamo, N. Collaert, C. Merckling

    In this work, we report on the growth of pseudomorphic and highly doped InAs(Si)/GaSb(Si) heterostructures on p-type (001)-oriented GaSb substrate and the fabrication and characterization of n+/p+ Esaki tunneling diodes. We particularly study the influence of the Molecular Beam Epitaxy shutter sequences on the structural and electrical characteristics of InAs(Si)/GaSb(Si) Esaki diodes structures. We use real time Reflection High Electron Diffraction analysis to monitor different interface stoichiometry at the tunneling interface. With Atomic Force Microscopy, X-ray diffraction and Transmission Electron Microscopy analyses, we demonstrate that an “InSb-like” interface leads to a sharp and defect-free interface exhibiting high quality InAs(Si) crystal growth contrary to the “GaAs-like” one. We then prove by means of Secondary Ion Mass Spectroscopy profiles that Si-diffusion at the interface allows the growth of highly Si-doped InAs/GaSb diodes without any III-V material deterioration. Finally, simulations are conducted to explain our electrical results where a high Band to Band Tunneling (BTBT) peak current density of Jp = 8 mA/μm2 is achieved.

    更新日期:2017-12-27
  • Monte Carlo simulation of induction time and metastable zone width; stochastic or deterministic?
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-26
    Noriaki Kubota

    The induction time and metastable zone width (MSZW) measured for small samples (say 1 mL or less) both scatter widely. Thus, these two are observed as stochastic quantities. Whereas, for large samples (say 1000 mL or more), the induction time and MSZW are observed as deterministic quantities. The reason for such experimental differences is investigated with Monte Carlo simulation. In the simulation, the time (under isothermal condition) and supercooling (under polythermal condition) at which a first single crystal is detected are defined as the induction time t and the MSZW ΔT for small samples, respectively. The number of crystals just at the moment of t and ΔT is unity. A first crystal emerges at random due to the intrinsic nature of nucleation, accordingly t and ΔT become stochastic. For large samples, the time and supercooling at which the number density of crystals N/V reaches a detector sensitivity (N/V)det are defined as t and ΔT for isothermal and polythermal conditions, respectively. The points of t and ΔT are those of which a large number of crystals have accumulated. Consequently, t and ΔT become deterministic according to the law of large numbers. Whether t and ΔT may stochastic or deterministic in actual experiments should not be attributed to change in nucleation mechanisms in molecular level. It could be just a problem caused by differences in the experimental definition of t and ΔT.

    更新日期:2017-12-27
  • Characterization of nonpolar a-plane GaN epi-layers grown on high-density patterned r-plane sapphire substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-24
    Daiki Jinno, Shunya Otsuki, Shogo Sugimori, Hisayoshi Daicho, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki

    To reduce the number of threading dislocations (TDs) in nonpolar a-plane GaN (a-GaN) epi-layers grown on flat r-plane sapphire substrates (r-FSS), we investigated the effects on the crystalline quality of the a-GaN epi-layers of high-density patterned r-plane sapphire substrates (r-HPSS), the patterns of which were placed at intervals of several hundred nanometers. Two types of r-HPSS, the patterns of which had diameters and heights on the order of several hundred nanometers (r-NHPSS) or several micrometers (r-MHPSS), were prepared with conventional r-FSS. The effect of these r-HPSS on the a-GaN epi-layers was demonstrated by evaluating the surface morphology and the crystalline quality of the epi-layers. The surfaces of the a-GaN epi-layer grown on r-FSS and r-NHPSS were pit-free and mirror-like, whereas the surface of the a-GaN epi-layer grown on r-MHPSS was very rough due to the large, irregular GaN islands that grew on the patterns, mainly at the initial growth stage. The crystalline quality of the a-GaN epi-layer grown on r-NHPSS was better than that of the a-GaN epi-layer grown on r-FSS. We confirmed that there were fewer TDs in the a-GaN epi-layer grown on r-NHPSS than there were in the a-GaN epi-layer grown on r-FSS. The TDs propagating to the surface in a-GaN epi-layer grown on r-NHPSS were mainly generated on the flat sapphire regions between the patterns. Interestingly, it was also found that the TDs that propagated to the surface concentrated with a periodic pitch along the c-axis direction. The TD densities of a-GaN epi-layers grown on r-FSS and r-NHPSS were estimated to be approximately 5.0×1010 and 1.5×109 cm-2, respectively. This knowledge will contribute to the further development of a-GaN epi-layers for high-performance devices.

    更新日期:2017-12-27
  • Heteroepitaxy of orientation-patterned nonlinear optical materials
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-23
    Vladimir L. Tassev, Shivashankar R. Vangala, Rita D. Peterson, Michael Snure

    We report some recent results on thick heteroepitaxial growth of GaP on GaAs substrates and on orientation-patterned (OP) GaAs templates conducted in a hot-wall horizontal quartz reactor for Hydride Vapor Phase Epitaxy. The growths on the plain substrates resulted in up to 500 µm thick GaP with smooth surface morphology (RMS <1–2 nm) and high crystalline quality (FWHM = 100–150 arcsec), comparable to the quality of the related homoepitaxial growths of GaP on GaP. Up to 300 µm thick OPGaP quasi-phase matching structures with excellent domain fidelity were also heteroepitaxially grown with high reproducibility on OPGaAs templates in support of frequency conversion laser source development for the mid and longwave infrared. We studied the GaAsxP1-x ternary transition layer that forms between the growing film and the substrate. We also undertook steps to determine some important characteristics of heteroepitaxy such as thickness of the pseudomorphous growth and periodicity of the expected misfit dislocations. The formation of these and some other defects and their distribution within the layer thickness was also investigated. Samples were characterized by Nomarski optical microscopy, transmission optical measurements, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The focus was predominantly on the interface and, more precisely, on what influence the pre-growth surface treatment of the substrate has on the initial and the following stages of growth, as well on the mechanisms of the strain relaxation from the lattice and thermal mismatch between layer and substrate. The efforts to accommodate the growing film to the foreign substrate by engineering an intermediate buffer layer were extended to thick growths of GaAsxP1-x ternary with the idea to combine in one material the best of the nonlinear properties of GaP and GaAs that are strictly relevant to the pursuit applications.

    更新日期:2017-12-27
  • Selective area growth of InAs nanowires from SiO2/Si(111) templates direct-written by focused helium ion beam technology
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-18
    Che-Wei Yang, Wei-Chieh Chen, Chieh Chou, Hao-Hsiung Lin

    We report on the selective area growth of InAs nanowires on patterned SiO2/Si (111) nano-holes, prepared by focused helium ion beam technology. We used a single spot mode, in which the focused helium ion beam was fixed on a single point with a He+-ion dosage, ranging from 1.5 pC to 8 pC, to drill the nano-holes. The smallest hole diameter achieved is ∼8 nm. We found that low He+-ion dosage is able to facilitate the nucleation of (111)B InAs on the highly mismatched Si, leading to the vertical growth of InAs nanowires (NWs). High He-ion dosage, on the contrary, severely damaged Si surface, resulting in tilted and stripe-like NWs. In addition to titled NW grown from (111)A InAs domain, a new titled growth direction due to defect induced twinning was observed. Cross-sectional TEM images of vertical NWs show mixed wurtizite (WZ) and zincblende (ZB) phases, while WZ phase dominants. The stacking faults resulting from the phase change is proportional to NW diameter, suggesting that the critical diameter of phase turning is larger than 110 nm, the maximum diameter of our NWs. Period of misfit dislocation at the InAs/Si interface of vertical NW is also found larger than the theoretical value when the diameter of heterointerface is smaller than 50 nm, indicating that the small contact area is able to accommodate the large lattice and thermal mismatch between InAs and Si.

    更新日期:2017-12-18
  • Effect of power history on the shape and the thermal stress of a large sapphire crystal during the Kyropoulos process
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-15
    Tran Phu Nguyen, Hsiao-Tsun Chuang, Jyh-Chen Chen, Chieh Hu

    In this study, the effect of the power history on the shape of a sapphire crystal and the thermal stress during the Kyropoulos process are numerically investigated. The simulation results show that the thermal stress is strongly dependent on the power history. The thermal stress distributions in the crystal for all growth stages produced with different power histories are also studied. The results show that high von Mises stress regions are found close to the seed of the crystal, the highly curved crystal surface and the crystal-melt interface. The maximum thermal stress, which occurs at the crystal-melt interface, increases significantly in value as the crystal expands at the crown. After this, there is reduction in the maximum thermal stress as the crystal lengthens. There is a remarkable enhancement in the maximum von Mises stress when the crystal-melt interface is close to the bottom of the crucible. There are two obvious peaks in the maximum Von Mises stress, at the end of the crown stage and in the final stage, when cracking defects can form. To alleviate this problem, different power histories are considered in order to optimize the process to produce the lowest thermal stress in the crystal. The optimal power history is found to produce a significant reduction in the thermal stress in the crown stage.

    更新日期:2017-12-16
  • Heterointerface study of InAs/GaSb nanoridge heterostructures grown by metal organic chemical vapor deposition on V-grooved Si (001) substrates
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-15
    Billy Lai, Qiang Li, Kei May Lau

    InAs/GaSb nanoridge heterostructures were grown on V-grooved (001) Si by metal organic chemical vapor deposition. Combining the aspect ratio trapping process and a low temperature GaAs buffer, we demonstrated high quality GaSb nanoridge templates for InAs/GaSb heterostructure growth. Two different interfaces, a transitional GaAsSb and an InSb-like interface, were investigated when growing these heterostructures. A 500 ° ° C growth temperature in conjunction with a GaAsSb interface was determined to produce the optimal interface, properly compensating for the tensile strain accumulated when growing InAs on GaSb. Without the need for a complicated switching sequence, this GaAsSb-like interface utilized at the optimized temperature is the initial step towards InAs/GaSb type II superlattice and other device structures integrated onto Si.

    更新日期:2017-12-16
  • Effects of In-situ UV Irradiation on the Uniformity and Optical Properties of GaAsBi Epi-layers Grown by MBE
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-14
    Daniel A. Beaton, M. Steger, T. Christian, A. Mascarenhas

    In-situ UV illumination influences the incorporation dynamics of bismuth adatom in GaAs. Here we use the inherent variation of the fluence across the sample to explore the role of the incident irradiation. With illumination it is found that steady state growth processes are achieved more quickly resulting in more abrupt interfaces, as well as uniform GaAs1-x GaAs 1 - x Bix Bi x epi-layers. Comparisons of low temperature photoluminescence spectra show an increasing density of clusters of incorporated bismuth atoms with decreasing incident fluence.

    更新日期:2017-12-15
  • Si impurity concentration in nominally undoped Al0.7Ga0.3N grown in a planetary MOVPE reactor
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-14
    J. Jeschke, A. Knauer, M. Weyers

    The unintentional silicon incorporation during the metalorganic vapor phase epitaxy (MOVPE) of nominally undoped Al0.7Ga0.3N in a Planetary Reactor under various growth conditions was investigated. Dependent on growth temperature, pressure and V/III ratio, Si concentrations of below 1 × 1016 up to 4 × 1017 cm-3 were measured. Potential Si sources are discussed and, by comparing samples grown in a SiC coated reactor setup and in a TaC coated setup, the SiC coatings in the reactor are identified as the most likely source for the unintentional Si doping at elevated temperatures above 1080°C. Under identical growth conditions the background Si concentration can be reduced by up to an order of magnitude when using TaC coatings.

    更新日期:2017-12-15
  • Synthesis and single crystal growth of perovskite semiconductor CsPbBr3
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-13
    Mingzhi Zhang, Zhiping Zheng, Qiuyun Fu, Zheng Chen, Jianle He, Sen Zhang, Cheng Chen, Wei Luo

    As a typical representative of all-inorganic lead halide perovskites, cesium lead bromine (CsPbBr3) has attracted significant attention in recent years. The direct band gap semiconductor CsPbBr3 has a wide band gap of 2.25 eV and high average atomic number (Cs: 55, Pb: 82 and Br: 35), which meet most of the requirements for detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photoconductivity response. However, the growth of large volume CsPbBr3 single crystals remains a challenge. In this paper, the synthesis of CsPbBr3 polycrystalline powders by a chemical co-precipitation method was investigated and the optimum synthesis conditions were obtained. A large CsPbBr3 single crystal of 8 mm diameter and 60 mm length was obtained by a creative electronic dynamic gradient (EDG) method. X-ray diffraction (XRD) patterns and X-ray rocking curve showed that the CsPbBr3 crystal preferentially oriented in the (110) direction and had a low dislocation density and small residual stress in the crystal. The IR and UV-Vis transmittance and temperature-dependent photoluminescence (PL) spectra showed the crystal had a good basic optical performance. The almost linear current-voltage (I-V) curves implied good ohmic contact between the electrodes and crystal surfaces. The resistivity of the crystal was calculated 109-1010 Ω·cm. The above results showed that the quality of the obtained crystal had met the demand of optoelectronic applications.

    更新日期:2017-12-15
  • Morphological and Structural Evolution on the Lateral Face of the Diamond Seed by MPCVD Homoepitaxial Deposition
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-13
    Jianli Chen, Guangjian Wang, Chengjun Qi, Ying Zhang, Song Zhang, Yongkuan Xu, Jianmin Hao, Zhanping Lai, Lili Zheng

    This paper presents a recent study on the morphology variation on the lateral faces of a HPHT diamond seed by MPCVD method. Raman spectroscopy and SEM were used to display the morphological and structural evolution of the grown diamond. It has been observed that different types of carbon allotropes were deposited at different heights of the substrate. At the bottom of the substrate, the feature of the lateral face was dominated by vertically aligned graphite nanoplatelets. An increment of sp3 and sp2 hybridized carbons was found to take over at the region of approximately 100 μm above from the bottom followed by the increasing-size diamond grains. The high quality single crystalline diamond was formed at the top of the lateral face. We proposed that the temperature gradient around the substrate is responsible for variable features on the substrate lateral face. By optimizing the growth temperature, we have obtained an enlarged area of the lateral face with high quality single crystalline diamond. This work will provide both sp2 on sp3 carbon materials for the development of electrochemical sensors and electrodes, and a foundation for the diamond lateral face growth with high quality and high purity.

    更新日期:2017-12-15
  • Finite Element Design for the HPHT Synthesis of Diamond
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-13
    Rui Li, Mingming Ding, Tongfei Shi

    The finite element method is used to simulate the steady-state temperature field in diamond synthesis cell. The 2D and 3D models of the China-type cubic press with large deformation of the synthesis cell was established successfully, which has been verified by situ measurements of synthesis cell. The assembly design, component design and process design for the HPHT synthesis of diamond based on the finite element simulation were presented one by one. The temperature field in a high-pressure synthetic cavity for diamond production is optimized by adjusting the cavity assembly. A series of analysis about the influence of the pressure media parameters on the temperature field are examined through adjusting the model parameters. Furthermore, the formation mechanism of wasteland was studied in detail. It indicates that the wasteland is inevitably exists in the synthesis sample, the distribution of growth region of the diamond with hex-octahedral is move to the center of the synthesis sample from near the heater as the power increasing, and the growth conditions of high quality diamond is locating at the center of the synthesis sample. These works can offer suggestion and advice to the development and optimization of a diamond production process.

    更新日期:2017-12-15
  • Growth and Performance Research of Tb3Ga5O12 Magneto-optical Crystal
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-13
    Weizhao Jin, Jingxin Ding, Li Guo, Qi Gu, Chun Li, Liangbi Su, Anhua Wu, Fanming Zeng

    Tb3Ga5O12 (TGG) crystal was grown successfully by the Czochralski method in an iridium crucible with radio frequency (RF)-induced heating under high purity 80%N2+20%CO2 atmosphere. None impurity peaks could be found in the XRD patterns compared to standard cards of TGG. Transmittance spectrum was investigated in the visible-near infrared region (VIS-NIR) at room temperature, which indicated the TGG crystal had high transmittance at 500-1100 nm. The Faraday rotations, Verdet constants and magnetic susceptibility of (111), (100), (110) of as-grown crystal have been discussed in detail confirming that Faraday effects of the TGG crystals are anisotropic which is related with magnetic susceptibility, and the Faraday effects of [111] have been proved to be the best, and the Verdet constants of [111] was also investigated at different wavelength at room temperature. The thermal conductivity and laser induced damage threshold of the crystal were also analyzed in detailed.

    更新日期:2017-12-15
  • The role of ultrasound in controlling the liquid-liquid phase separation and nucleation of vanillin polymorphs I and II
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-13
    P. Parimaladevi, S. Supriya, K. Srinivasan

    The influence of ultrasound on liquid-liquid phase separation (LLPS) and polymorphism of vanillin in aqueous solution has been investigated for the first time by varying the ultrasonic parameters such as power, pulse rate and insonation time at ambient condition. Results reveal that the application of ultrasound controls the impact of LLPS and accelerates the nucleation of vanillin within a short period at lower levels of ultrasonic process parameters, and also enhances the quality of the nucleated crystals. Moreover, the application of ultrasound induces the nucleation of rare and metastable polymorph of vanillin Form II in aqueous solution. But, at higher levels of power, pulse rate and insonation time, the rate of LLPS is found increased and the quality of the crystals becomes deteriorated. Morphology of the nucleated polymorphs were identified through optical microscopy and confirmed by optical goniometry. The internal structure and thermal stability of the grown stable Form I and metastable Form II of vanillin were confirmed through powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) analyses. Further, results suggest that the ultrasound has profound effect in controlling the LLPS and nucleation of vanillin polymorphs in aqueous solution.

    更新日期:2017-12-15
  • Analytical solution of the problem of dissolved gas segregation in melt by the plain crystallization front
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-13
    A.A. Chernov, A.A. Pil’nik

    Analytical solution of the segregation problem is found for the arbitrary crystal growth law using the quasi-steady-state approximation. The segregation in this case is caused by the displacement of dissolved gas by moving plane crystallization front. The effect of solidification shrinkage on the crystallization process was taken into account. The comparison made between obtained solution and existing exact solutions shows good agreement. It is shown that in the case of “equilibrium crystallization” (when the growth rate is inversely proportional to time) the solution of the problem becomes self-similar. In this case gas concentration at the crystallization front instantly increases to a certain value and than stays the same during the whole process. At the same time the diffusion layer thickness increases proportionally to time. The conditions for the inevitability of gaseous release leading to the formation of pores in solidified material is formulated for the general case.

    更新日期:2017-12-13
  • Enhanced B doping in CVD-grown GeSn:B using B δ-doping layers
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-12
    David Kohen, Anurag Vohra, Roger Loo, Wilfried Vandervorst, Nupur Bhargava, Joe Margetis, John Tolle

    Highly doped GeSn material is interesting for both electronic and optical applications. GeSn:B is a candidate for source-drain material in future Ge pMOS device because Sn adds compressive strain with respect to pure Ge, and therefore can boost the Ge channel performances. A high B concentration is required to obtain low contact resistivity between the source-drain material and the metal contact. To achieve high performance, it is therefore highly desirable to maximize both the Sn content and the B concentration. However, it has been shown than CVD-grown GeSn:B shows a trade-off between the Sn incorporation and the B concentration (increasing B doping reduces Sn incorporation). Furthermore, the highest B concentration of CVD-grown GeSn:B process reported in the literature has been limited to below 1×1020 cm-3. Here, we demonstrate a CVD process where B δ-doping layers are inserted in the GeSn layer. We studied the influence of the thickness between each δ-doping layers and the δ-doping layers process conditions on the crystalline quality and the doping density of the GeSn:B layers. For the same Sn content, the δ-doping process results in a 4-times higher B doping than the co-flow process. In addition, a B doping concentration of 2×1021 cm-3 with an active concentration of 5×1020 cm-3 is achieved.

    更新日期:2017-12-12
  • Unzipping and movement of Lomer-type edge dislocations in Ge/GeSi/Si(001) heterostructures
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-11
    Yu.B. Bolkhovityanov, A.S. Deryabin, A.K. Gutakovskii, L.V. Sokolov

    Edge dislocations in face-centered crystals are formed from two mixed dislocations gliding along intersecting {111} planes, forming the so-called Lomer locks. This process, which is called zipping, is energetically beneficial. It is experimentally demonstrated in this paper that a reverse process may occur in Ge/GeSi strained buffer/Si(001) heterostructures under certain conditions, namely, decoupling of two 60° dislocations that formed the Lomer-type dislocation, i.e., unzipping. It is assumed that the driving force responsible for separation of Lomer dislocations into two 60° dislocations is the strain remaining in the GeSi buffer layer.

    更新日期:2017-12-11
  • Growth method for AIIIBV and AIVBVI heterostructures
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-08
    I.V. Fedorchenko, A.R. Kushkov, D.S. Gaev, O.I. Rabinovich, S.F. Marenkin, S.I. Didenko, S.A. Legotin, M.N. Orlova, A.A. Krasnov

    The results of nanoscale islet films grown by AIIIBV and AIVBVI incongruent evaporation compounds are discussed. The surface morphology structure was studied by atomic-force microscopy. It is shown that the distribution density and the characteristic dimensions of nanostructures depend on the evaporation temperature.

    更新日期:2017-12-10
  • Growth and Spectroscopic properties of Er:Yb:LuPO4 and Er:Yb:Ce:LuPO4 crystals
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-08
    Jie He, Bing Teng, Degao Zhong, Liang Yang, Yalin Xu, Min Zhu, Yao Meng, Lina Liu, Fang Yuan, Mengdi Fan, Xiaoqian Wu, Yang Che, Jie Tang

    In this work, we report the growth and spectroscopic properties of high-quality Er:Yb:LuPO4 and Er:Yb:Ce:LuPO4 crystals which are grown by the high-temperature solution method for the first time to the best of our knowledge. The maximum polarization absorption cross sections and the full-width of half-maximum of the Er:Yb:LuPO4 are (3.32×10-20 cm2, 17 nm) and (2.41×10-20 cm2, 19 nm) for σ- and π-polarization, respectively. The up-conversion luminescence spectra and near-infrared luminescence spectra of both Er:Yb:LuPO4 and Er:Yb:Ce:LuPO4 crystals were recorded under 980 nm pumping. The results exhibit that the up-conversion energy losses are remarkably reduced in Er:Yb:Ce:LuPO4 crystal. Consequently, the luminescence intensity in the waveband of 1.5∼1.6 μm of Er:Yb:Ce:LuPO4 is increased by two times compared to Er:Yb:LuPO4.

    更新日期:2017-12-10
  • Investigating new activators for small-bandgap LaX3 (X = Br, I) scintillators
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-08
    Daniel Rutstrom, Robyn Collette, Luis Stand, Matthew Loyd, Yuntao Wu, Merry Koschan, Charles L. Melcher, Mariya Zhuravleva

    Luminescence and scintillation properties of Bi3+, Sb3+, and Eu2+-doped LaI3 and LaBr3 were explored. Out of the three dopants investigated, Eu2+ was the most promising new activator for small-bandgap LaX3 (X = Br, I) and was further studied in the mixed-halide LaBr3-xIx. Crystals were grown from the melt using the vertical Bridgman method. LaBr3:Eu2+ 0.5% (mol) had the most favorable scintillation properties with a light output of 43,000 ph/MeV and 6% energy resolution at 662 keV. Performance of LaBr3-xIx:Eu2+ worsened for most samples as iodide concentration was increased. Room-temperature scintillation of LaI3:Eu2+ 0.1% and 0.5% was observed and is the first case of room-temperature emission reported for doped LaI3.

    更新日期:2017-12-10
  • Effect of controlled crucible movement on melting process and carbon contamination in Czochralski silicon crystal growth
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-08
    Xin Liu, Xue-Feng Han, Satoshi Nakano, Koichi Kakimoto

    In Czochralski silicon (CZ-Si) crystal growth, packed Si chunks experience collapse and volume shrinkage during the melting process. The axial movements of the crucible and the melting of the Si feedstock lead to dynamic thermal and flow fields and affect mass transport. To study the effect of crucible movement on the melting process and carbon (C) contamination, the cases of fixed and lifting crucible were investigated by the transient global simulation with dynamic mesh deformation. The gap width between the gas-guide and the top surface of Si feedstock was kept constant during the crucible lifting process. Impurity and species transport in Si feedstock and argon gas was investigated for the cases with the fixed and lifting crucibles. The comparison of C accumulation processes indicated that the lifting crucible case resulted in higher C contamination than that found in the fixed crucible case. Furthermore, lifting crucible cases with different gap widths were investigated to elaborate strategies for controlling the crucible movement for its effect on the melting process and C contamination in CZ-Si crystal growth. It was observed that the optimum gap width for C reduction results from the trade-off between the back diffusion and gas convection.

    更新日期:2017-12-10
  • Effects of Deposition Temperature and Ammonia Flow on Metal-Organic Chemical Vapor Deposition of Hexagonal Boron Nitride
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-08
    Anthony Rice, Andrew Allerman, Mary Crawford, Thomas Beechem, Taisuke Ohta, Douglas Medlin, Catalin Spataru, Jeffrey Figiel, Michael Smith

    The use of metal-organic chemical vapor deposition at high temperature is investigated as a means to produce epitaxial hexagonal boron nitride (hBN) at the wafer scale. Several categories of hBN films were found to exist based upon precursor flows and deposition temperature. Low, intermediate, and high NH3 flow regimes were found to lead to fundamentally different deposition behaviors. The low NH3 flow regimes yielded discolored films of boron sub-nitride. The intermediate NH3 flow regime yielded stoichiometric films that could be deposited as thick films. The high NH3 flow regime yielded self-limited deposition with thicknesses limited to a few mono-layers. A Langmuir-Hinshelwood mechanism is proposed to explain the onset of self-limited behavior for the high NH3 flow regime. Photoluminescence characterization determined that the intermediate and high NH3 flow regimes could be further divided into low and high temperature behaviors with a boundary at 1500 °C. Films deposited with both high NH3 flow and high temperature exhibited room temperature free exciton emission at 210 nm and 215.9 nm.

    更新日期:2017-12-10
  • 3D Numerical simulation of free surface shape during the crystal growth of floating zone (FZ) silicon
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-08
    Xue-Feng Han, Xin Liu, Satoshi Nakano, Hirofumi Harada, Yoshiji Miyamura, Koichi Kakimoto

    In FZ growth processes, the stability of the free surface is important in the production of single crystal silicon with high quality. To investigate the shape of the free surface in the FZ silicon crystal growth, a 3D numerical model that included gas and liquid phases was developed. In this present study, 3D Young-Laplacian equations have been solved using the Volume of Fluid (VOF) Model. Using this new model, we predicted the 3D shape of the free surface in FZ silicon crystal growth. The effect of magnetic pressure on shape of free surface has been considered. In particular, the free surface of the eccentric growth model, which could not be previously solved using he 2D Young-Laplacian equations, was solved using the VOF model. The calculation results are validated by the experimental results.

    更新日期:2017-12-10
  • Reduction of Threading Dislocation Density in SiGe Epilayer on Si (001) by Lateral Growth Liquid-Phase Epitaxy
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-07
    Andrew J. O'Reilly, Nathaniel J. Quitoriano

    Si0.973Ge0.027 epilayers were grown on a Si (001) substrate by a lateral liquid-phase epitaxy (LLPE) technique. The lateral growth mechanism favoured the glide of misfit dislocations and inhibited the nucleation of new dislocations by maintaining the thickness less than the critical thicknesses for dislocation nucleation and greater than the critical thickness for glide. This promoted the formation of an array of long misfit dislocations parallel to the [110] growth direction and reduced the threading dislocation density to 103 cm-2, two orders of magnitude lower than the seed area with an isotropic misfit dislocation network.

    更新日期:2017-12-10
  • Large-scale grain growth in the solid-state process: From “Abnormal” to “Normal”
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-06
    Minhong Jiang, Shengnan Han, Jingwei Zhang, Jiageng Song, Chongyan Hao, Manjiao Deng, Lingjing Ge, Zhengfei Gu, Xinyu Liu

    Abnormal grain growth (AGG) has been a common phenomenon during the ceramic or metallurgy processing since prehistoric times. However, usually it had been very difficult to grow big single crystal (centimeter scale over) by using the AGG method due to its so-called occasionality. Based on the AGG, a solid-state crystal growth(SSCG) method was developed. The greatest advantages of the SSCG technology are the simplicity and cost-effectiveness of the technique. But the traditional SSCG technology is still uncontrollable. This article first summarizes the history and current status of AGG, and then reports recent technical developments from AGG to SSCG, and further introduces a new seed-free, solid-state crystal growth(SFSSCG) technology. This SFSSCG method allows us to repeatedly and controllably fabricate large-scale single crystals with appreciable high quality and relatively stable chemical composition at a relatively low temperature, at least in (K0.5Na0.5)NbO3(KNN) and Cu-Al-Mn systems. In this sense, the exaggerated grain growth is no longer 'Abnormal' but 'Normal' since it is able to be artificially controllable and repeated now. This article also provides a crystal growth model to qualitatively explain the mechanism of SFSSCG for KNN system. Compared with the traditional melt and high temperature solution growth methods, the SFSSCG method has the advantages of low energy consumption, low investment, simple technique, composition homogeneity overcoming the issues with incongruent melting and high volatility. This SFSSCG could be helpful for improving the mechanical and physical properties of single crystals, which should be promising for industrial applications.

    更新日期:2017-12-06
  • MOVPE growth and transport characterization of Bi2-xSbxTe3-ySey films
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-06
    P.I. Kuznetsov, G.G. Yakushcheva, B.S. Shchamkhalova, V.A. Jitov, A.G. Temiryazev, V.E. Sizov, V.O. Yapaskurt

    We present a first study of films of the quaternary Bi2-xSbxTe3-ySey solid solutions on (0001) sapphire substrates grown by atmospheric pressure MOVPE. Trimethylbismuth , trimethylantimony, diisopropylselenide and diethyltelluride were used as precursors. To passivate the free bonds of the substrate and to improve the epitaxy, a thin (15 nm) ZnTe buffer layer was first grown. EDX analysis of the films grown at a temperature of 445 °C upon a 10-fold excess of chalcogen in the vapor phase indicates on their compliance with V2VI3 stoichiometry. AFM and SEM investigations showed that at the initial stage of deposition the Stranski-Krastanov growth mode is dominant. Complete coalescence of nanoislands occurs at a thickness about 60 nm and further film formation is in the 2D layer-by-layer growth mode. A high mole fraction of antimony in the vapor phase leads to bad crystalline quality of the films and even to their discontinuity. Transport properties of the Bi2-xSbxTe3-ySey films were evaluated using Van der Pauw Hall effect measurements in the range of temperatures of 10 - 300 K. Some films are always n- or p-type; in other samples the change of conductivity from p- to n-type was observed when the temperature decreases.

    更新日期:2017-12-06
  • Advanced Crystal Growth Techniques for Thallium Bromide Semiconductor Radiation Detectors
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-06
    Amlan Datta, Piotr Becla, Christo Guguschev, Shariar Motakef

    Thallium Bromide (TlBr) is a promising room-temperature radiation detector candidate with excellent charge transport properties. Currently, Travelling Molten Zone (TMZ) technique is widely used for growth of semiconductor-grade TlBr crystals. However, there are several challenges associated with this type of crystal growth process including lower yield, high thermal stress, and low crystal uniformity. To overcome these shortcomings of the current technique, several different crystal growth techniques have been implemented. These include: Vertical Bridgman (VB), Physical Vapor Transport (PVT), Edge-defined Film-fed Growth (EFG), and Czochralski Growth (Cz). Techniques based on melt pulling (EFG and Cz) were demonstrated for the first time for semiconductor grade TlBr material. The viability of each process along with the associated challenges for TlBr growth has been discussed. The purity of the TlBr crystals along with its crystalline and electronic properties were analyzed and correlated with the growth techniques.

    更新日期:2017-12-06
  • A novel magneto-optical crystal Yb:TbVO4
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-05
    Xianchao Zhu, Heng Tu, Zhanggui Hu

    Highly transparent Yb:TbVO4 single crystal with dimensions of Ø27×41 mm3 alomost without scattering defects has been successfully grown by Czochralski technique. The spectra, thermal properties and laser-induced damage threshold were investigated in detailed. The Faraday rotation (FR) measurement was carried out by means of extinction method. The Verdet constant comes up to 80 rad·m-1T-1 at 1064 nm, significantly larger than TbVO4 (58 rad·m-1T-1) and TGG (40 rad·m-1T-1) reported. Meanwhile, the as-grown crystal presents lower absorption coefficient and higher magneto-optical figure of merit at measured wavelength in comparison with TGG. Moreover, the crystal exhibits a substantially improved extinction ratio (42 dB) in contrast with TbVO4 (29 dB), and exceeds the highest value of TGG (40 dB). These advantages make Yb:TbVO4 a highly promising magneto-optical material candidate for optical isolators in the visible-near infrared region.

    更新日期:2017-12-06
  • Study on Growth Techniques and Macro Defects of Large-Size Nd:YAG Laser Crystal
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-05
    Jiliang Quan, Xin Yang, Mingming Yang, Decai Ma, Jinqiang Huang, Yunzhong Zhu, Biao Wang

    Large-size neodymium-doped yttrium aluminum garnet (Nd:YAG) single crystals were grown by the Czochralski method. The extinction ratio and wavefront distortion of the crystal were tested to determine the optical homogeneity. Moreover, under different growth conditions, the macro defects of inclusion, striations, and cracking in the as-grown Nd:YAG crystals were analyzed. Specifically, the inclusion defects were characterized using scanning electron microscopy and energy dispersive spectroscopy. The stresses of growth striations and cracking were studied via a parallel plane polariscope. These results demonstrate that improper growth parameters and temperature fields can enhance defects significantly. Thus, by adjusting the growth parameters and optimizing the thermal environment, high-optical-quality Nd:YAG crystals with a diameter of 80 mm and a total length of 400 mm have been obtained successfully.

    更新日期:2017-12-06
  • Modification of growth interface of CdZnTe crystals in THM process by ACRT
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-05
    Boru Zhou, Wanqi Jie, Tao Wang, Liying Yin, Fan Yang, Binbin Zhang, Shouzhi Xi, Jiangpeng Dong

    The accelerated crucible rotation technique (ACRT) was introduced in the traveling heater method (THM) growth process of detector-grade CdZnTe (CZT) crystals to regulate the convection in the melt and to modify the growth interface morphology. Several ingots with the diameter of 53 mm were grown by THM with/without ACRT. The ingots were quenched during the growth to show both macroscopic and microscopic morphologies of the growth interfaces. The results show that by using ACRT the growth interface can be changed from a concave one to the flat or even convex one depending on the ACRT parameters, which is favorable for reducing nucleation in the melt to get larger CZT grains. Meanwhile, by using ACRT in THM process, the microscopic interface was changed from a diffused one to cellular or even planar one (at suitable ACRT parameters), through which the trapped Te inclusions was decreased for one order. An ingot grown by THM with constant rotation rate of 40 rpm was also grown, which have also reduced the interface curvature in macro-scale and Te inclusions to some extent, but the effects are not as significant as ACRT with high crucible rotation rate.

    更新日期:2017-12-06
  • Control of optical properties of YAG crystals by thermal annealing
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-05
    S. Tkachenko, P. Arhipov, I. Gerasymov, D. Kurtsev, S. Vasyukov, V. Nesterkina, N. Shiran, P. Mateichenko, O. Sidletskiy

    Optical properties of YAG crystals grown and annealed under different atmosphere conditions have been compared. Simultaneously we have registered the surface composition of crystals and content of basic admixtures in the crystals grown under the reducing conditions. Unlike YAG grown under weakly oxidizing conditions in Ir crucibles and bleached under oxidizing annealing, YAGMo crystals grown in Mo crucibles under reducing Ar+CO atmosphere can be bleached by both oxidizing and reducing thermal annealing. The bleaching of YAGMo is not reversed by further annealing under any available conditions. Mechanisms of this phenomenon have been discussed, including a possible role of admixtures in elimination of color centers in YAG grown under the reducing conditions.

    更新日期:2017-12-06
  • P-type single-crystalline ZnO films obtained by (Na,N) dual implantation through dynamic annealing process
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-05
    Zhiyuan Zhang, Jingyun Huang, Shanshan Chen, Xinhua Pan, Lingxiang Chen, Zhizhen Ye

    Single-crystalline ZnO films were grown by plasma-assisted molecular beam epitaxy technique on c-plane sapphire substrates. The films have been implanted with fixed fluence of 130kev Na and 90kev N ions at 460°C. It is observed that dually-implanted single crystalline ZnO films exhibit p-type characteristics with hole concentration in the range of 1.24×1016-1.34×1017 cm-3, hole mobilities between 0.65-8.37 cm2V-1s-1, and resistivities in the range of 53.3-80.7 Ωcm by Hall-effect measurements. There are no other secondary phase appearing, with (002) (c-plane) orientation after ion implantation as identified by the X-ray diffraction pattern. It is obtained that Na and N ions were successfully implanted and activated as acceptors measured by XPS and SIMS results. Also compared to other similar studies, lower amount of Na and N ions make p-type characteristics excellent as others deposited by traditional techniques. It is concluded that Na and N ion implantation and dynamic annealing are essential in forming p-type single-crystalline ZnO films.

    更新日期:2017-12-06
  • Morphological instability of lamellar structures in directionally solidified Ni–Ni3Si alloys
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-12-05
    Lufeng Wei, Zhilong Zhao, Jianjun Gao, Kai Cui, Jingying Guo, Sen Chen, Lin Liu

    The morphological instability of lamellar structures in Ni–Ni3Si eutectic and hypereutectic alloys directionally solidified at low growth rates was investigated. The first instability in large lamellar structures was zigzag instability, which formed curved lamellae. A zigzag pattern was first displayed in three dimensions. The diffusion-limited growth of the Ni3Si phase decreased phase width and spacing, consequently causing zigzag instability. The reduced spacing was observed at λ/λave= 0.9. After zigzag instability, the microstructure of the eutectic alloy turned into a labyrinth structure and lamellar fragmentation. However, in hypereutectic alloys, shape transition from lamellae to rods occurred, in turn, by the broken lamellae or elongated rods to dumbbell-shaped rods, peanut-shaped rods, and circular rods.

    更新日期:2017-12-06
  • In-situ growth mode control of AlN on SiC substrate by sublimation closed space technique
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-28
    Daichi Dojima, Koji Ashida, Tadaaki Kaneko

    For the growth of AlN single crystal with large diameter and low dislocation density on SiC substrate by physical vapor transport (PVT), a dislocation blocking buffer layer (DBBL) has been simply developed by optimizing the AlN growth parameters such as temperature gradient (ΔT), substrate temperature (Tsub), and N2 partial pressure (PN2) at the initial growth stage. Increase in ΔT resulted in the formation of an abrupt AlN/SiC interface due to the suppression of inhomogeneous thermal decomposition at the interface and the subsequent AlN unstable island growth. The well-defined AlN/SiC interface played an important role in controlling the two kinds of different AlN growth mode in-situ as functions of Tsub and PN2. One is a continuous step-flow growth mode and the other is a discontinuous platelet-like growth. The discontinuous AlN layer, consisting of thin AlN platelets and air-gaps inserted between the two adjacent platelets, acted as the DBBL. By introducing the DBBL at the initial growth stage, followed by the step-flow growth, continuous AlN layer with dislocation density of 1.7 × 106 cm-2 was achieved at a total growth thickness of 60 μm, which is two orders of magnitude lower than the previously reported value.

    更新日期:2017-11-29
  • Au crystal growth on natural occurring Au—Ag aggregate elucidated by means of precession electron diffraction (PED).
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-28
    Josep Roqué Rosell, Joaquim Portillo Serra, Thomas Aiglsperger, Sergi Plana-Ruiz, Trifon Trifonov, Joaquín Antonio Proenza

    In the present work, a lamella from an Au—Ag aggregate found in Ni-laterites has been examined using Transmission Electron Microscope to produce a series of Precision Electron Diffraction (PED) patterns. The analysis of the structural data obtained, coupled with Energy Dispersive X-ray microanalysis, made it possible to determine the orientation of twinned native gold growing on the Au—Ag aggregate. The native Au crystal domains are found to have grown at the outermost part of the aggregate whereas the inner core of the aggregate is an Au—Ag alloy (∼4 wt% Ag). The submicron structural study of the natural occurring Au aggregate points to the mobilization and precipitation of gold in laterites and provides insights on Au aggregates development at supergene conditions. This manuscript demonstrates the great potential of electron crystallographic analysis, and in particular, PED to study submicron structural features of micron sized mineral aggregates by using the example of a gold grain found in a Ni-laterite deposits.

    更新日期:2017-11-28
  • Three-dimensional morphologies of inclined equiaxed dendrites growing under forced convection by phase-field-lattice Boltzmann method
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-26
    Shinji Sakane, Tomohiro Takaki, Munekazu Ohno, Yasushi Shibuta, Takashi Shimokawabe, Takayuki Aoki

    Three-dimensional growth morphologies of equiaxed dendrites growing under forced convection, with their preferred growth direction inclined from the flow direction, were investigated by performing large-scale phase-field lattice Boltzmann simulations on a graphical-processing-unit supercomputer. The tip velocities of the dendrite arms with their preferred growth directions inclined toward the upstream and downstream directions increased and decreased, respectively, as a result of forced convection. In addition, the tip velocities decreased monotonically as the angle between the preferred growth direction and the upstream direction increased. Here, the degree of acceleration of the upstream tips was larger than the degree of deceleration of the downstream tips. The angles between the actual tip growth directions and the preferred growth direction of the dendrite arms exhibited a characteristic change with two local maxima and two local minima.

    更新日期:2017-11-27
  • Spatial distribution of structural defects in Cz-seeded directionally solidified silicon ingots: An etch pit study
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-26
    A. Lantreibecq, M. Legros, N. Plassat, JP. Monchoux, E. Pihan

    The PV properties of wafers processed from Cz-seeded directionally solidified silicon ingots suffer from variable structural defects. In this study, we draw an overview on the types of structural defects encountered in the specific case of full <100> oriented growth. We found micro twins, background dislocations, and subgrains boundaries. We discuss the possible links between thermomechanical stresses and growth processes with spatial evolution of both background dislocation densities and subgrain boundaries length.

    更新日期:2017-11-27
  • Control of interface shape during high melting sesquioxide crystal growth by HEM technique
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-24
    Kaiwei Hu, Lili Zheng, Hui Zhang

    During crystal growth in heat exchanger method (HEM) system, the shape of the growth interface changes with the proceeding of the growth process, which limits the crystal size and reduces the quality of the crystal. In this paper, a modified HEM system is proposed to control the interface shape for growth of sesquioxide crystals. Numerical simulation is performed to predict heat transfer, melt flow and interface shape during growth of high melting sesquioxide crystals by the heat exchanger method. The results show that a flat or slightly convex interface shape is beneficial to reduce the solute pileup in front of the melt/crystal interface and decrease the radial temperature gradient inside the crystal during growth of sesquioxide crystals. The interface shape can be controlled by adjusting the gap size d and lower resistance heater power during growth. The growth rate and the crystal/melt interface position can be obtained by two measured temperatures.

    更新日期:2017-11-24
  • Redshift and Blueshift of GaNAs/GaAs Mutiple Quatum Wells Induced by Rapid Thermal Annealing
    J. Cryst. Growth (IF 1.751) Pub Date : 2017-11-24
    Yijun Sun, Zhiyuan Cheng, Qiang Zhou, Ying Sun, Jiabao Sun, Yanhua Liu, Meifang Wang, Zhen Cao, Zhi Ye, Mingsheng Xu, Yong Ding, Peng Chen, Michael Heuken, Takashi Egawa

    The effects of rapid thermal annealing (RTA) on the optical properties of GaNAs/GaAs mutiple quantum wells (MQWs) grown by chemical beam epitaxy (CBE) are studied by photoluminescence (PL) at 77K. The results show that the optical quality of the MQWs improves significantly after RTA. With increasing RTA temperature, PL peak energy of the MQWs redshifts below 1023K, while it blueshifts above 1023K. Two competitive processes which occur simultaneously during RTA result in redshift at low temperature and blueshift at high temperature. It is also found that PL peak energy shift can be explained neither by nitrogen diffusion out of quantum wells nor by nitrogen reorganization inside quantum wells. PL peak energy shift can be quantitatively explained by a modified recombination coupling model in which redshift nonradiative recombination and blueshift nonradiative recombination coexist. The results obtained have significant implication on the growth and RTA of GaNAs material for high performance optoelectronic device application.

    更新日期:2017-11-24
  • 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
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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