气相输运法大尺寸ZnO单晶生长的传输过程控制

研究了化学气相传输法(CVT)生长ZnO单晶的传输过程、动力学和生长机理,分析了CVT法的传输机理、效率以及温场对传输速率和晶体生长的影响.利用气相-固相单晶成核和生长动力学理论研究了制约单晶生长速度和晶体质量的因素.我们得到的不同条件下ZnO单晶CVT生长的实验结果和现象与理论分析一致,获得了ZnO单晶生长的理想条件和高质量的大尺寸ZnO单晶材料.     

气相输运法大尺寸ZnO单晶生长的传输过程控制

研究了化学气相传输法(CVT)生长ZnO单晶的传输过程、动力学和生长机理,分析了CVT法的传输机理、效率以及温场对传输速率和晶体生长的影响.利用气相-固相单晶成核和生长动力学理论研究了制约单晶生长速度和晶体质量的因素.我们得到的不同条件下ZnO单晶CVT生长的实验结果和现象与理论分析一致,获得了ZnO单晶生长的理想条件和高质量的大尺寸ZnO单晶材料.     

物理气相传输法生长大尺寸AlN晶体及其性质表征

利用物理气相传输法生长了直径40～50 mm、厚约8～10 mm的AlN多晶锭,最大晶粒尺寸为5 mm.用喇曼散射和阴极荧光谱研究了AlN晶体的结晶质量、缺陷和结构特性.分析了不同温度下AlN晶体的导电特性,并确定在AlN晶体中存在一个激活能约为0.98eV的深能级缺陷.结合这些结果分析了PVT法生长条件对AlN体单晶生长和晶体质量的影响.     

物理气相传输法生长大尺寸AlN晶体及其性质表征

利用物理气相传输法生长了直径40～50 mm、厚约8～10 mm的AlN多晶锭,最大晶粒尺寸为5 mm.用喇曼散射和阴极荧光谱研究了AlN晶体的结晶质量、缺陷和结构特性.分析了不同温度下AlN晶体的导电特性,并确定在AlN晶体中存在一个激活能约为0.98eV的深能级缺陷.结合这些结果分析了PVT法生长条件对AlN体单晶生长和晶体质量的影响.     

大尺寸碳化硅单晶生长环境研究

针对基于物理气相输运法的碳化硅(SiC)单晶生长系统,考虑对流换热的影响建立了传热与传质数学模型,并采用数值模拟的方法研究了其生长系统内的温度场与气相流场.研究表明:坩埚内温度、温度梯度以及加热效率随线圈匝间距与线圈直径的增加而逐渐降低.旋转坩埚可有效解决因线圈螺旋形状而导致的温度场不均匀性.通过不断调整线圈与坩埚之间的相对高度,可保证高品质晶体生长所需的最优温度场环境.此外,坩埚内径尺寸的增加,会加剧其内部自然对流效应.     

氨化Ga2O3和金属Ga粒混合镓源制备高质量GaN纳米线

在管式炉中用化学气相沉积(CVD)法在高温下用金做催化剂,首次通过氨化Ga2O3和金属Ga粒组成的混合镓源制备出高质量的GaN纳米线.运用SEM,TEM,XRD以及Ramah,PL等表征手段分析了氮化镓纳米线的形貌、结构以及发光性质.最后着重探讨了通过改变镓源的构成、氨化温度以及镓源和生长衬底间的距离等生长条件,研究了...     

液相法制备GaN单晶体研究进展

回顾了GaN单晶体的液相生长法研究进展,主要介绍了高压氮气溶液法(HPNSG)、Na助溶剂法以及氨热法的原理、生长条件及其研究进展。液相法可以制备相比于气相法更高质量的GaN晶体。其中HPNSG可以制备位错密度低于102cm-2的GaN晶体,氨热法可以生产出高质量的2英寸(1英寸=2.54 cm)GaN晶体,重点介绍了Na助溶剂法的生长设备及最新研究成果,目前该方法已经可以生长直径超过2 cm、高度约为1.2 cm的无位错块体GaN晶体。对液相法生长GaN晶体的应用前景进行了预测,认为液相法制备的高质量GaN晶体作为大功率、高可靠性GaN电子器件理想衬底,会发挥越来越重要的作用。     

VLS机制下SiC晶须的生长

采用化学气相沉积(CVD)法以气-液-固(VLS)机制生长了碳化硅(SiC)晶须,系统研究了基片表面的气流状况、生长温度和反应室总气压等对SiC晶须形貌的影响。研究结果表明:当基片表面存在较强的平流状态时,以生长SiC薄膜为主,很难形成晶须;生长温度及反应室总气压对晶须的直径有较大影响,合适的生长温度以及较高的总压有利于晶须的生长。     

溶菌酶晶体形貌的原子力显微成像观测

为研究蛋白质晶体的生长机理,采用气相扩散法制备溶菌酶晶体,使用原子力显微成像技术观测了溶菌酶晶体(101)生长面的形貌.发现溶菌酶晶体(101)面生长呈现螺旋住错的特征,其台阶平均高度为2.9 nm,相当于单分子层的厚度.而以前在高过饱和度条件下得到的溶菌酶晶体的AFM图像显示为二维成核生长机理,其台阶高度为双分子层的厚度5.6 nm.这说明气相扩散法制备蛋白质晶体时,由于溶液的过饱和度较小,溶菌酶在溶液中可能不形成多聚物而是以单个分子的形式结合到晶体上,即(101)面的主要生长单元并非具有43螺旋结构的四聚体,而是溶菌酶单分子.这一结果为蛋白质晶体生长机理的探索提供了实验依据,是对溶菌酶晶体生长单元认识的补充.     

磷锗锌晶体生长技术研究进展

磷锗锌（ZnGeP₂）单晶体是一种性能优异的红外非线性光学晶体材料,被广泛应用于各种先进的光学器件。研究ZnGeP₂晶体的生长方法,对低成本制备大体积、高质量的ZnGeP₂晶体具有重要意义。介绍了ZnGeP₂晶体的结构和应用领域,给出了ZnGeP₂多晶合成与单晶生长技术研究发展的最新动态,并基于晶体生长原理以及生长条件控制方法的差异,综述了水平温度梯度冷凝（HGF）法、液封提拉（LEC）法、高压气相（HPVT）法和垂直布里奇曼（VB）法4种主要的ZnGeP₂单晶体生长方法的优缺点;重点阐述了较成熟的HGF和VB法生长ZnGeP₂晶体的影响因素和研究进展,提出了ZnGeP₂单晶制备技术存在的主要问题和今后的发展方向。     

MOCVD外延生长GaN材料的技术进展

第三代半导体材料GaN由于具有优良性质使其在微电子和光电子领域有广阔的应用前景,目前制备GaN的方法主要有分子束(MBE)、氯化物气相外延(HVPE)、金属有机物化学气相沉积(MOCVD)。其中HVPE技术制备GaN的速度最快,适合制备衬底材料;MBE技术制备GaN的速度最慢;而MOCVD制备速度适中。因而MOCVD在外延生长GaN材料方面得到广泛应用。介绍了MOCVD法外延生长GaN材料的基本理论、发展概况、利用MOCVD法外延生长GaN材料的技术进展。认为应结合相关技术发展大面积、高质量GaN衬底的制备技术,不断完善缓冲层技术,改进和发展横向外延技术,加快我国具有国际先进水平的MOCVD设备的研发速度,逐步打破进口设备的垄断。     

Nanohomojunction (GaN) and Nanoheterojunction (InN) Nanorods on One‐Dimensional GaN Nanowire Substrates

The formation of homojunctions and heterojunctions on two‐dimensional (2D) substrates plays a key role in the device performance of thin films. Accelerating the progress of device fabrication in nanowires (NWs) also necessitates a similar understanding in the one‐dimensional (1D) system. Nanohomojunction (GaN on GaN) and nanoheterojunction (InN on GaN) nanorods (NRs) were formed in a two‐step growth process by a vapor–liquid–solid (VLS) mechanism. Ga₂O₃ nanoribbons were formed using Ni as catalyst in a chemical vapor deposition (CVD) technique and then completely converted to GaN NWs with NH₃ as reactant gas. An Au catalyst is used in the second step of the VLS process to grow GaN and InN NRs on GaN NWs using CVD techniques. A morphological study showed the formation of nanobrushes with different structural symmetries and sub‐symmetries in both homogeneous and heterogeneous systems. Structural characterizations showed nearly defect‐free growth of nanohomojunction (GaN) and nanoheterojunction (InN) NRs on 1D GaN NW substrates.     

额外HCl和氮化对HVPE GaN生长的影响

在氢化物气相外延(HVPE)生长Ga N过程中,发现了一种在成核阶段向生长区添加额外HCl来改善Ga N外延薄膜质量的方法,并且讨论了额外HCl和氮化对Ga N形貌和质量的影响.两种方法都可以大幅度地改善Ga N的晶体质量和性质,但机理不同.氮化是通过在衬底表面形成Al N小岛,促进了衬底表面的成核和薄膜的融合;而添加额外HCl则被认为是通过改变生长表面的过饱和度引起快速成核从而促进薄膜的生长而改善晶体质量和性质的     

Influence of annealing porous templates in an ammonia atmosphere on gallium nitride growth behaviors in hydride vapor phase epitaxy

Porous templates were fabricated by hydrogen-etching metal organic chemical vapor deposited gallium nitride (GaN); these templates were used as substrates for the growth of GaN via hydride vapor phase epitaxy. The influence of annealing porous templates on GaN growth behavior was investigated. GaN epitaxied on the unannealing porous template followed the Volmer–Weber mode with the void preserved at the growth plane, whereas the GaN film on the annealed porous templates exhibited a layer-by-layer growth and filled the porous material. The GaN crystal quality was characterized by high-resolution XRD and CL, the results indicated that GaN grown with pores preserved at the template interface had a lower dislocation density than that grown with pores filled, and the best GaN film had a TD density of 10⁴ cm⁻².     

HVPE生长的高质量GaN纳米柱的光学性能

GaN纳米材料因具有优异的晶体质量和突出的光学性能及发射性能,日益受到关注.研究了一种利用氢化物气相外廷(HVPE)系统生长高质量的GaN纳米柱的方法.使用镍作为催化剂,在蓝宝石衬底上生长出了GaN纳米柱.在不同生长时间和不同HC1体积流量下制备了多组样品,使用扫描电子显微镜(SEM)、X射线衍射(XRD)和光致发光(PL)谱对样品进行了分析表征.测试结果表明,在较低的HC1体积流量下,生长2 min的样品具有较高的晶体质量和较好的光学性质.讨论了不同生长阶段的GaN纳米结构发光特性的变化规律,认为纳米结构所产生的表面态密度大小差异会造成带边峰位的红移和展宽.     

Reduction of Dislocation Density in HVPE-Grown GaN Epilayers by Using In Situ-Etched Porous Templates

In this paper, a method was demonstrated to reduce the dislocation density of GaN film grown by hydride vapor phase epitaxy (HVPE) on an in situ selective hydrogen-etched GaN/sapphire template. The dislocations regions were etched by hydrogen to form cavities. The porous structure was formed on the GaN template grown by metal organic chemical vapor deposition after in situ hydrogen etching. The etching condition was optimized by modulating the etching temperature, pressure, and etching time. Two-step buffer layer growth and high temperature GaN film deposition were carried on the porous template. The growth parameters were optimized to keep the porous structure unfilled. The dislocations originally located in etched cavities could not propagate to the next layer grown by HVPE. Therefore, the dislocation density could be significantly reduced. High crystal quality of GaN is obtained with a low dislocation density. The full width at half-maximum FWHM of (002) is 35 arcs, and the FWHM of (102) is 48 arcs.     

Hydride vapor phase epitaxy for gallium nitride substrate

Due to the remarkable growth rate compared to another growth methods for gallium nitride(GaN)growth,hydride vapor phase epitaxy(HVPE)is now the only method for mass product GaN substrates.In this review,commercial HVPE systems and the GaN crystals grown by them are demonstrated.This article also illustrates some innovative attempts to develop homebuilt HVPE systems.Finally,the prospects for the further development of HVPE for GaN crystal growth in the future are also discussed.     

Quantification of roughness and spatial distribution of dislocations in MBE and MOVPE grown LED heterostructures

A combination of nanoscale imaging techniques such as atomic force microscopy and scanning electron microscopy are used to investigate the relationship between surface morphology and height statistics of GaN cap layers in InGaN/GaN light emitting diode heterostructures. The investigated samples were grown in two very different growth regimes which lead to distinct characteristic superficial landscapes. We also report here on the introduction of a new methodological approach that adapt the concept of height-height correlation function, a well known statistical tool in the field of studies on rough surfaces. We evaluate to which extent the geometrical properties of the constitutive ‘bricks’ (hillocks for ammonia assisted molecular beam epitaxial film) and structural defects (dislocation pits for metal organic vapor phase epitaxial film) affects the statistical properties of heights of these GaN surfaces. Finally, we have studied the spatial distribution of dislocation pits in both the samples to assess the quantitative differences between these heterostructures of very distinct surface morphology.     

基于图形衬底生长的GaN位错机制分析

采用缺陷选择性腐蚀法结合光学显微镜及原子力显微镜(AFM)对金属有机化合物气相外延(MOVPE)在蓝宝石图形衬底(PSS)上生长的非掺杂GaN体材料的位错产生机制进行了研究,分析结果表明,位错来源于三个方面:一是"二步法"生长机制引入的位错;二是是由于图形衬底上不同区域GaN晶体相互连接时由于晶面不连续所造成的位错群;三是由于图形衬底制作工艺过程中引入的表面污染与损伤.     

GaN grown by hydride vapor phase epitaxy on p-type 6H-SiC layers

6H-SiC/GaN pn-heterostructures were grown by subsequent epitaxial growth of p-SiC by low temperature liquid phase epitaxy (LTLPE) and n-GaN by hydride vapor phase epitaxy (HVPE). For the first time, p-type epitaxial layers grown on 6H-SiC wafers were used as substrates for GaN HVPE growth. The GaN layers exhibit high crystal quality which was determined by x-ray diffraction. The full width at a half maximum (FWHM) for the ω-scan rocking curve for (0002) GaN reflection was ∼120 arcsec. The photoluminescence spectra for these films were dominated by band-edge emission. The FWHM of the edge PL peak at 361 nm was about 5 nm (80K).