缓冲层生长速率对GaSb薄膜二维生长的影响

用分子束外延(MBE)法在GaAs(100)衬底上生长GaSb薄膜,得到了GaSb薄膜的优化生长工艺条件.为了降低因晶格失配度较大所引起的位错密度,采用低温(LT)GaSb作为缓冲层,研究了缓冲层的生长速率对GaSb薄膜二维生长的影响,并以此说明缓冲层在GaSb薄膜生长中所起的作用.通过X射线双晶衍射仪和原子力显微镜测试分析,得到当低温GaSb缓冲层的生长速率为1.43μm/h时,GaSb外延层中的位错密度最小,晶体质量最好.     

NH3-MBE生长极化场二维电子气材料

介绍了用ＮＨ３－ＭＢＥ技术在蓝宝石Ｃ面上外延的高质量的ＧａＮ单层膜以及ＧＮ／ＡｌＮ／ＧａＮ极化感应二维电子气材料。外延膜都是Ｎ面材料。形成的二维电子气是“倒置二维电子气”。ＧａＮ单层膜的室温电子迁移率为３００ｃｍ＾２／Ｖｓ。二维电子气材料的迁移率为６８０ｃｍ＾２／Ｖｓ（ＲＴ）和１７００ｃｍ＾２／Ｖｓ（７７Ｋ）,相应的二维电子气的面密度为３．２＊１０＾１３ｃｍ＾－２（ＲＴ）和２．６ｘ１０＾１３ｃｍ＾     

InP低温缓冲层的表面形貌及对其外延层生长的影响

采用两步生长法用金属有机物气相外延技术在GaAs（100）衬底生长InP，用原子力显微镜探索了退火和未退火的低温缓冲层以及InP外延层的表面形貌，测量了他们的表面均方根值，讨论了低温缓冲层表面形貌随生长温度的变化以及退火对其表面形貌的影响，并分析外延层与低温缓）中层表面形貌的依赖关系，外延层表面形貌均方根值与XRD测量值一致，在450℃生长低温缓）中层，外延层有最好的表面形貌。     

RF-MBE生长AlGaN/GaN二维电子气材料

用射频等离子体辅助分子束外延技术 (RF -MBE)在C面蓝宝石衬底上外延了高质量的GaN膜以及AlGaN/GaN极化感应二维电子气材料 .所外延的GaN膜室温背景电子浓度为 2× 10 17cm-3 ,相应的电子迁移率为 177cm2 /Vs;GaN (0 0 0 2 )X射线衍射摇摆曲线半高宽 (FWHM)为 6arcmin .;AlGaN/GaN极化感应二维电子气材料的室温电子迁移率为 730cm2 /Vs ,相应的电子气面密度为 7.6× 10 12 cm-2 ;用此二维电子气材料制作的异质结场效应晶体管 (HFET)室温跨导达 5 0mS/mm (栅长 1微米 ) ,截止频率达 13 .2 5GHz(栅长 0 .5微米 ) ,可在 30 0℃下工作     

OLEDs中CuPc缓冲层作用的AFM与XPS研究

利用AFM对CuPc/ITO样品表面进行扫描,发现其生长较均匀,基本上覆盖了ITO表面的缺陷,且针孔较少.通过样品表面和界面的XPS谱图分析,进一步证实了这一结果,同时发现,CuPc可以抑制ITO中的化学组分向空穴传输层的扩散.有利于器件的性能的改善和寿命的提高.     

不同厚度对分子束外延生长GaSb薄膜的影响

采用分子束外延(MBE)在GaAs衬底上生长GaSb薄膜,为了减小因晶格失配度较大所引起的位错密度,采用低温GaSb作为缓冲层.通过X射线双晶衍射仪和原子力显微镜分析得出,当低温GaSb缓冲层的厚度为20nm时,GaSb外延层中的位错密度最小,晶体质量最好.此外,缓冲层和外延层的厚度共同对GaSb薄膜晶体质量和表面形貌产生影响.     

沉积温度对高温超导带材YBiO3缓冲层外延生长的影响

采用脉冲激光沉积(PLD)方法,在LaAlO3(001)基片上研究了沉积温度对用作高温超导带材缓冲层YBiO3结晶的影响.结果表明,随着沉积温度的升高,YBiO3缓冲层结晶质量提高,取向趋于完美,表面较为平整.当沉积温度为700℃时,单晶外延的YBiO3与LaAlO3基片的外延关系为:YBiO3(001)// LaAlO3(001)和YBiO3[110]//LaAlO3[100],其晶格失配度为1.3%,平均粗糙度约为3.4nm.     

N离子注入改性SnO2缓冲层及其CdTe太阳电池应用

使用等离子注入技术对SnO_2薄膜进行N离子注入改性,进行方块电阻、光学透过、表面形貌、Kelvin探针和X射线光电子能谱(XPS)表征,并将其作为缓冲层应用到CdTe太阳电池中。研究结果发现,对于30nm厚的SnO_2缓冲层,经过30s、10min不同时间N离子注入以后,其300~800nm波长范围透过率有所降低,而体电阻率则明显增加,特别是N离子注入10min的SnO_2缓冲层,表面出现很多凹孔,呈蜂窝状结构,且对后续沉积的CdS层表面形貌产生了明显影响。Kelvin探针表征结果显示,随着N离子注入时间的延长,SnO_2缓冲层功函数逐渐增加,最高达到约5.075eV,比本征SnO_2缓冲层的功函数高出0.15eV。XPS测试结果显示,N离子注入10min后,SnO_2缓冲层N1s结合能峰位向低结合能方向发生了明显移动,而O1s结合能峰位则向高结合能方向移动了,且表面区非晶格氧所占比例增大。对比电池结果,有N离子注入改性SnO_2缓冲层的电池与无缓冲层的电池相比,效率从10%左右增加到12%以上,最高达到12.47%,其中开路电压提高最为显著,从约750mV提高到790mV以上,提升了约5%,电池的整体均匀性也明显改善。     

退火温度对RF磁控溅射ZnO薄膜力学性能的影响

采用X射线衍射分析(XRD),原子力显微镜(AFM)及纳米压痕技术测试分析了多晶ZnO薄膜的晶格结构和力学性能.薄膜的制备采用了射频(RF)磁控溅射方法,并分别在不同温度下进行了退火处理.XRD分析显示随着退火温度的上升,薄膜的晶粒尺寸逐步增大,且C轴取向显著增强.压痕测试结果表明,由于尺寸效应的影响,硬度随退火温度的变化有明显的趋势,从2.5GPa(常温下)逐步增加到5.5GPa(4500C),随着温度的进一步上升,硬度值又逐步下降到4.5GPa(650℃).弹性模量整体随退火温度的变化并不呈现明显的规律,但在450℃和200℃下退火分别有最大值26.7GPa和最小值21.5GPa,这是由于尺寸效应与晶格取向的双重作用的结果.测试结果表明适当的退火处理对ZnO薄膜的结晶品质与力学性能有明显的改善.     

MgxZn1-xO单晶薄膜的分子束外延生长及结构表征

用等离子辅助分子束外延(P-MBE)的方法,在蓝宝石c-平面上外延生长了MgxZn1-xO合金薄膜.在0≤x≤0.2范围内MgxZn1-xO薄膜保持着六角纤锌矿结构不变.原位反射式高能电子衍射图样和X射线双晶衍射谱的结果表明生长的样品是单晶薄膜.随着x值逐渐增大,Mg2+离子逐渐进入ZnO的晶格,X射线双晶衍射测得样品的(002)取向的半高宽度从0.249°增加到0.708°,表明结晶质量逐渐下降,(002)方向的X射线衍射峰向大角度方向移动,晶格常数c由5.205(A)减小到5.185(A).透射光谱的结果表明,合金薄膜的吸收边随着Mg离子的掺入逐渐向高能侧移动,室温光致发光谱出现很强的紫外发光(NBE)峰,没有观察到深能级(DL)发射,且随着Mg掺入量的增加,紫外发光峰有明显的蓝移,这与透射光谱的结果是相吻合的.     

射频等离子体分子束外延GaN的极性研究

对采用射频等离子体分子束外延（RF-plasma MBE)生长得到的GaN进行极性研究。由于镓极性（Ga-polar)比氮极性（N－polar)有更好的化学稳定性，通过比较RF－plasma MBE生长得到的不同GaN样品对光辅助湿法刻蚀的稳定性，发现缓冲层生长条件对GaN外延层的极性有着重要影响：较高缓冲层生长温度得到的GaN外延层表现为N－polar，较低缓冲层生长温度得到的GaN外延层表现为Ga-polar。     

GaN buffer layer growth by MOCVD using a thermodynamic non-equilibrium model

In this work, a gallium nitride (GaN) buffer layer was grown on a sapphire substrate (α-Al₂O₃) in a horizontal reactor by low pressure metal-organic chemical vapor deposition (LP-MOCVD). Trimethylgallium (TMGa) and ammonia (NH₃) were precursors of gallium and nitrogen, respectively, and hydrogen (H₂) was used as carrier gas. TMGa and NH₃ fluxes were kept constant, with flow rates of 3.36 μmole/min and 0.05 standard liter/min, respectively. The fluence of hydrogen was also kept constant with the flux rate of 4.5 standard liter/min. GaN was deposited at 550 °C and 100 mbar. According to the X-ray diffraction spectra, a buffer layer was formed with a wurtzite structure, which is the stable phase. The thermodynamic affinities were estimated as A₁ = 175.9 kJ/mole and A₂ = 62.88 kJ/mole.     

Influence of AlN buffer layer thickness and deposition methods on GaN epitaxial growth

A gallium nitride (GaN) epitaxial layer was grown by metal-organic chemical vapor deposition (MOCVD) on Si (111) substrates with aluminum nitride (AlN) buffer layers at various thicknesses. The AlN buffer layers were deposited by two methods: radio frequency (RF) magnetron sputtering and MOCVD. The effect of the AlN deposition method and layer thickness on the morphological, structural and optical properties of the GaN layers was investigated. Field emission scanning electron microscopy showed that GaN did not coalesce on the sputtered AlN buffer layer. On the other hand, it coalesced with a single domain on the MOCVD-grown AlN buffer layer. Structural and optical analyses indicated that GaN on the MOCVD-grown AlN buffer layer had fewer defects and a better aligned lattice to the a- and c-axes than GaN on the sputtered AlN buffer layer.     

The role of the Zn buffer layers in the structural and photoluminescence properties of ZnO films on Zn buffer layers deposited by RF magnetron sputtering

Highly c-axis oriented ZnO thin films were grown on Si (100) substrates with Zn buffer layers. Effects of the Zn buffer layer thickness on the structural and optical qualities of ZnO thin films were investigated for the ZnO films with the buffer layers 90, 110, and 130 nm thick using X-ray diffraction (XRD), photoluminescence (PL) and atomic force microscopy (AFM) analysis techniques. It was confirmed that the quality of a ZnO thin film deposited by RF magnetron sputtering was substantially improved by using a Zn buffer layer. The highest ZnO film quality was obtained with a Zn buffer layer 110 nm thick. The surface roughness of the ZnO thin film increases as the Zn buffer layer thickness increases.     

Synthesis and characterization of heteroepitaxial GaN films on Si(111)

We report crack-free and single-crystalline wurtzite GaN heteroepitaxy layers have been grown on Si (111) substrate by metal-organic chemical vapor deposition(MOCVD). Synthesized GaN epilayer was characterized by X-ray diffraction(XRD), atomic force microscope (AFM) and Raman spectrum. The test results show that the GaN crystal reveals a wurtzite structure with the <0001> crystal orientation and XRD ω-scans showed a full width at half maximum (FWHM) of around 583 arcsec for GaN grown on Si substrate with an HT-AlN buffer layer. In addition, the Raman peaks of E₂^high and A₁(LO) phonon mode in GaN films have an obvious redshit comparing to bulk GaN eigen-frequency, which most likely due to tensile strain in GaN layers. But the AO phonon mode of Si has a blueshit which shows that the Si substrate suffered a compressive strain. And we report that the AlN buffer layer plays a role for releasing the residual stress in GaN films.     

Fabrication of GaN epitaxial thin film on InGaZnO4 single-crystalline buffer layer

Epitaxial (0001) films of GaN were grown on (111) YSZ substrates using single-crystalline InGaZnO₄ (sc-IGZO) lattice-matched buffer layers by molecular beam epitaxy with a NH₃ source. The epitaxial relationships are (0001)_GaN//(0001)_IGZO//(111)_YSZ in out-of-plane and [112¯0]_GaN//[112¯0]_IGZO//[11¯0]_YSZ in in-plane. This is different from those reported for GaN on many oxide crystals; the in-plane orientation of GaN crystal lattice is rotated by 30° with respect to those of oxide substrates except for ZnO. Although these GaN films showed relatively large tilting and twisting angles, which would be due to the reaction between GaN and IGZO, the GaN films grown on the sc-IGZO buffer layers exhibited stronger band-edge photoluminescence than GaN grown on a low-temperature GaN buffer layer.     

Optimization of GaN nucleation layer deposition conditions on sapphire substrates in HVPE system

The influence of deposition conditions of nucleation GaN layer on the properties of high-temperature GaN layer, grown on sapphire substrates, was investigated. The hydride vapor phase epitaxy (HVPE) three-section horizontal hot-wall furnace technique was applied. Various temperatures, HCl flows and time intervals of nucleation layer growth were utilized. Based on previous studies the following experimental conditions were selected: temperature was kept at 450 or 570 °C, and HCl flows were 8 or 10 sccm/min. The duration of nucleation layer deposition was 5, 7 and 9 min. The scanning electron microscopy technique was applied for the investigation of nucleation layer morphology after migration. Thick GaN layers were deposited during the three-step growth process at 1060 °C. Samples with various surface morphologies were obtained. Photoluminescence spectra and X-ray measurements were performed, which permitted clarifications of the influence of growth conditions of the nucleation layer on the properties of high-temperature layers.     

Growth of GaN on SiC/Si substrates using AlN buffer layer by hot-mesh CVD

GaN films were grown on SiC/Si (111) substrates by hot-mesh chemical vapor deposition (CVD) using ammonia (NH₃) and trimetylgallium (TMG) under low V/III source gas ratio (NH₃/TMG = 80). The SiC layer was grown by a carbonization process on the Si substrates using propane (C₃H₈). The AlN layer was deposited as a buffer layer using NH₃ and trimetylaluminum (TMA). GaN films were formed and grown by the reaction between NH_x radicals, generated on a tungsten hot mesh, and the TMG molecules. The GaN films with the AlN buffer layer showed better crystallinity and stronger near-band-edge emission compared to those without the AlN layer.     

Effects of SiC buffer layer growth temperature on the residual strain of GaN/SiC/Si thin films

Effects of SiC buffer layers were studied on the residual strain of GaN films grown on 3C-SiC/Si (111) substrates. It was clearly observed by Raman scattering measurement that the residual strain of the GaN/Si is reduced by inserting the SiC intermediate layer. Furthermore, residual strain within the GaN/SiC/Si films decreased when the growth temperature of the SiC buffer layer decreased. It was proposed that the irreversible creep phenomenon occurs during the high temperature growth of SiC, affecting nature of the residual strain within the SiC and the GaN layers.     

MOCVD growth of GaN layer on InN interlayer and relaxation of residual strain

100 nm InN layer was grown on sapphire c-plane using a metal-organic chemical vapor deposition (MOCVD) system. Low temperature (LT) GaN layer was grown on InN layer to protect InN layer from direct exposure to hydrogen flow during high temperature (HT) GaN growth and/or abrupt decomposition. Subsequently, thick HT GaN layer (2.5 μm thick) was grown at 1000 °C on LT GaN/InN/sapphire template. Microstructure of epilayer-substrate interface was investigated by transmission electron microscopy (TEM). From the high angle annular dark field TEM image, the growth of columnar structured LT GaN and HT GaN with good crystallinity was observed. Though thickness of InN interlayer is assumed to be about 100 nm based on growth rate, it was not clearly shown in TEM image due to the InN decomposition. The lattice parameters of GaN layers were measured by XRD measurement, which shows that InN interlayer reduces the compressive strain in GaN layer. The relaxation of compressive strain in GaN layer was also confirmed by photoluminescence (PL) measurement. As shown in the PL spectra, red shift of GaN band edge peak was observed, which indicates the reduction of compressive strain in GaN epilayer.