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.

Evolution of microstructure, stress and dislocation of AlN thick film on nanopatterned sapphire substrates by hydride vapor phase epitaxy

A crack-free AlN film with 4.5 μm thickness was grown on a 2-inch hole-type nano-patterned sapphire substrates(NPSSs) by hydride vapor phase epitaxy(HVPE). The coalescence, stress evolution, and dislocation annihilation mechanisms in the AlN layer have been investigated. The large voids located on the pattern region were caused by the undesirable parasitic crystallites grown on the sidewalls of the nano-pattern in the early growth stage. The coalescence of the c-plane AlN was hindered by these three-fold crystallites and the special triangle void appeared. The cross-sectional Raman line scan was used to characterize the change of stress with film thickness, which corresponds to the characteristics of different growth stages of AlN. Threading dislocations(TDs) mainly originate from the boundary between misaligned crystallites and the c-plane AlN and the coalescence of two adjacent c-plane AlN crystals, rather than the interface between sapphire and AlN.

Effect of Substrate Nitridation on Properties of Thick GaN Film Grown by Hydride Vapour Phase Epitaxy

Thick GaN films were grown on the sapphire substrate by hydride vapour phase epitaxy. The properties of GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia prior to the GaN growth initiation. The crystalline quality of GaN films revealed by high resolution X-ray diffraction were strongly dependent on the nitridation time, which determined substrate surface topography. The different nitridation schemes strongly affected the morphology of GaN overlayers resulting in the blue shift of the main excitonic peak in photoluminescence spectra at room temperature.

Growth and doping of bulk GaN by hydride vapor phase epitaxy

Doping is essential in the growth of bulk GaN substrates,which could help control the electrical properties to meet the requirements of various types of GaN-based devices.The progresses in the growth of undoped,Si-doped,Ge-doped,Fedoped,and highly pure GaN by hydride vapor phase epitaxy(HVPE) are reviewed in this article.The growth technology and precursors of each type of doping are introduced.Besides,the influence of doping on the optical and electrical properties of GaN are presented in detail.Furthermore,the problems caused by doping,as well as the methods to solve them are also discussed.At last,highly pure GaN is briefly introduced,which points out a new way to realize high-purity semi-insulating(HPSI) GaN.

Growth of a-Plane GaN Films on r-Plane Sapphire by Combining Metal Organic Vapor Phase Epitaxy with the Hydride Vapor Phase Epitaxy

Hydride vapor phase epitaxy （HVPE） is utilized to grow nonpolar a-plane GaN layers on r-plane sapphire templates prepared by metal organic vapor phase epitaxy （MOVPE）. The surface morphology and microstructures of the samples are characterized by atomic force microscopy. The full width at half maximum （FWHM） of the HVPE sample shows a W-shape and that of the MOVPE sample shows an M-shape plane with the degree of 0 in the high-resolution x-ray diffraction （HRXRD） results. The surface morphology attributes to this significant anisotropic. HRXRD reveals that there is a significant reduction in the FWHM, both on-axis and off-axis for HVPE GaN are compared with the MOVPE template. The decrease of the FWHM of E2 （high） Raman scat tering spectra further indicates the improvement of crystal quality after HVPE. By comparing the results of secondary- ion-mass spectroscope and photoluminescence spectrum of the samples grown by HVPE and MOVPE, we propose that C-involved defects are originally responsible for the yellow luminescence.

The fabrication of AlN by hydride vapor phase epitaxy

Aluminum nitride(AlN)is the promising substrates material for the epitaxial growth ofⅢ-nitrides devices,such as high-power,high-frequency electronic,deep ultraviolet optoelectronics and acoustic devices.However,it is rather difficult to obtain the high quality and crack-free thick AlN wafers because of the low surface migration of Al adatoms and the large thermal and lattice mismatches between the foreign substrates and AlN.In this work,the fabrication of AlN material by hydride vapor phase epitaxy(HVPE)was summarized and discussed.At last,the outlook of the production of AlN by HVPE was prospected.

Porous AlN films grown on C-face SiC by hydride vapor phase epitaxy

We report the growth of porous AlN films on C-face SiC substrates by hydride vapor phase epitaxy(HⅤPE).The influences of growth condition on surface morphology,residual strain and crystalline quality of Al N films have been investigated.With the increase of theⅤ/Ⅲratio,the growth mode of Al N grown on C-face 6H-SiC substrates changes from step-flow to pit-hole morphology.Atomic force microscopy(AFM),scanning electron microscopy(SEM)and Raman analysis show that cracks appear due to tensile stress in the films with the lowestⅤ/Ⅲratio and the highestⅤ/Ⅲratio with a thickness of about 3μm.In contrast,under the mediumⅤ/Ⅲratio growth condition,the porous film can be obtained.Even when the thickness of the porous Al N film is further increased to 8μm,the film remains porous and crack-free,and the crystal quality is improved.

GaN substrate and GaN homo-epitaxy for LEDs:Progress and challenges

After a brief review on the progresses in GaN substrates by ammonothermal method and Na-flux method and hydride vapor phase epitaxy （HVPE） technology, our research results of growing GaN thick layer by a gas fow-rnodulated HVPE, removing the GaN layer through an efficient self-separation process from sapphire substrate, and modifying the uniformity of multiple wafer growth are presented. The effects of surface morphology and defect behaviors on the GaN homo-epitaxial growth on free standing substrate are also discussed, and followed by the advances of LEDs on GaN substrates and prospects of their applications in solid state lighting.

Growth Front Evolution of GaN Thin Films on Sapphire Substrate During HVPE

The growth front evolution of GaN thin films deposited on sapphire substrate by hydride vapor phase epitaxity has been studied with atomic force microscope. The evolution of the surface morphology presents four features of stage with the growth process. In initial growth stage, the surface is granular, and the typical grain diameter is about 250 nm for t =0.1 min. 3D growth plays a key role before the films come up to full coalescence, which causes a rough surface. After 0. 1 min the growth dimension decreases with the increase of lateral over growth, the surface roughness obviously decreases. From 0.4 min to 3 rain, the growth front roughness increases gradually, and the evolution of the surface roughness exhibits the characteristics of self-affined fractal. Beyond 3 min, the root-mean-square decreases gradually, which means the deposition behavior from hyper-2D growth gradually turns into layer growth mode with the increase of growth time.

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

载气流量对HVPE外延生长GaN膜光学性质的影响

研究了利用水平氢化物气相外延 (HVPE)系统在蓝宝石衬底上外延氮化镓 (Ga N)的生长规律 ,重点研究了作为载气的氮气流量对 Ga N膜的结构及光学性质的影响。观察到载气流量对预反应的强弱有很大影响 ,外延膜的质量和生长速度对载气流量极为敏感。当载气流量较小时 ,样品的 X射线衍射谱 (XRD)中出现了杂峰(1 0 -1 1 )和 (1 1 -2 0 ) ,相应的光致发光谱 (PL)中出现了黄带 (YL) ,靠近带边有杂质态。而当载气流量增大时 ,样品质量改善。Ga N外延膜的结构和光学性质的相关性表明深能级的黄带与生长过程中产生的非 c轴方向晶面有关 ,据此我们推测 :Ga空位与束缚在 (1 0 -1 1 )和 (1 1 -2 0 )等原子面上的杂质构成复合结构 ,这些复合结构所产生的深能级对黄带的发射有贡献 ;

HVPE外延GaN膜中黄带的光致发光激发谱研究

测量了氢化物气相外延方法生长的非特意掺杂和掺碳GaN外延膜的光致发光谱 ,并在光致发光谱峰位2 .2 5eV(5 5 0nm)附近分别测量了光致发光激发谱 ,对两者进行了比较 .从光致发光谱中发现掺碳使黄带明显增强 ,从光致发光激发谱中看到了掺碳引起的约 3.38～ 2 .6 7eV(36 7～ 4 6 5nn)范围内的特征激发带 .利用CC曲线模型说明了特征激发带和黄带之间的关系 ,分析了黄带的可能起因 .

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延(HVPE)系统生长高质量的Ga N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HCl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HCl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。

HVPE生长厚层GaN基片V/Ⅲ对结晶质量的影响

采用HVPE法,通过改变V/Ⅲ生长厚层GaN基片。分别采用X射线双晶衍射摇摆曲线、拉曼光谱及扫描探针显微镜进行生长晶体结晶质量和显微形貌分析。生长出表面光亮、无坑、无裂痕的60μm以上厚层GaN基片,并简要介绍厚层GaN基片生长过程中V/Ⅲ影响成核岛演变的规律。

衬底氮化对HVPE法生长GaN的影响

研究了衬底氮化过程对于氢化物气相外延 (HVPE)方法生长的GaN膜性质的影响。X射线衍射和原子力显微镜以及光荧光测量的结果表明 ,不同的氮化时间导致Al2 O3表面的成核层发生变化 ,进一步影响了外延层中的位错密度和应力分布。

HVPE生长室气流分布模拟及GaCl载气流量对GaN单晶生长的影响

采用计算流体力学软件Fluent对HVPE反应室进行了数值模拟,研究了GaCl载气流量对HVPE反应室气流分布的影响,发现GaCl载气流量是影响GaCl和NH3在衬底上均匀分布的重要因素。采用HVPE方法在不同GaCl载气流量下生长GaN单晶,研究了GaCl载气流量对GaN单晶质量的影响,得到了与模拟一致的结果。

大尺寸HVPE反应室生长GaN的数值模拟

利用有限元法对单片6英寸（1英寸=2.54 cm）Ga N衬底用氢化物气相外延（HVPE）生长系统的工艺参数进行了数值模拟和优化。通过建立反应室二维几何模型,依次改变HVPE系统中的Ga Cl,NH3和分隔气（N2）流速等主要参数进行数值模拟,研究分析了反应室内各反应物的浓度分布和衬底上Ga N的生长速率变化,同时考虑了涡旋分布以及Ga Cl出口管壁上寄生沉积等对衬底上Ga N生长的影响,并给出了HVPE系统高速率均匀生长Ga N的优化参数。模拟分析还表明,适当降低HVPE反应室内的压强可以改善衬底上Ga N生长的均匀性。

ZnO缓冲层的厚度对HVPE-GaN外延层的影响

为了得到高质量的GaN材料,首先在c面蓝宝石(Al2O3)衬底上射频磁控溅射不同厚度的ZnO缓冲层,然后采用氢化物气相外延(HVPE)法在ZnO缓冲层上生长约5.2μm厚的GaN外延层,研究ZnO缓冲层的厚度对GaN外延层质量的影响。用微分干涉显微镜(DIC)、扫描电子显微镜(SEM)、X射线衍射(XRD)和光致发光(PL)技术研究分析了GaN外延层的表面形貌、结晶质量和光学特性。结果表明,ZnO缓冲层的厚度对GaN外延层的特性有着重要的影响,200 nm厚的ZnO缓冲层最有利于高质量GaN外延层的生长。

基于蓝宝石衬底生长GaN的立式HVPE控制系统设计

为了实现氢化物气相外延(HVPE)技术在蓝宝石衬底上外延生长氮化镓(GaN)过程的全自动控制,进一步提高系统的精确性和稳定性,设计了一种新型HVPE控制系统。该控制系统选用可编程逻辑控制器(PLC)为控制器,采用组态王开发系统监控软件。利用模糊推理机制和仿真分析,设计模糊比例积分微分(PID)控制器,提高反应室温区控制的快速性与稳定性。构建大、小质量流量通路,精准控制HVPE系统压力与质量流量,并进行控制系统性能测试。结果表明,该控制系统能较好地实现对GaN生长过程的自动监控,成功在蓝宝石衬底上生长出高质量6英寸(1英寸=2.54 cm)GaN,与现有的HVPE制备技术及监控手段相比,其自动控制程度更高,系统实时响应更快,更具实际生产应用价值。

HVPE法生长GaN厚膜弯曲的分析

异质外延生长和降温过程中的失配会引起HVPE厚膜样品的弯曲,较大的弯曲会导致薄膜开裂和剥落。利用高分辨X射线衍射仪(XRD)分析,HVPE生长的不同厚度GaN样品的弯曲。对于同一个样品,X射线出射狭缝分别用1mm的标准狭缝和50μm的小狭缝测量,发现(0002)面摇摆曲线的半宽有明显变化。通过计算和比较,采用标准狭缝测得的(0002)面摇摆曲线的展宽是由弯曲和位错共同引起的,而弯曲表现得更为显著,小狭缝的展宽主要反应样品位错的信息。通过不同狭缝半宽的测量,得到了不同厚度GaN厚膜样品的曲率和位错密度。