立方相GaN的高温MOCVD生长

利用MOCVD技术在提高生长温度(900℃)下生长出了高质量的立方相GaN,生长速度提高到1.6μm/h.高温生长的GaN样品近带边峰室温光荧光半高宽为48meV,小于在830℃下生长的GaN样品.在ω扫描模式下,X射线衍射表明高温生长的GaN具有较小的(002)峰半高宽21′.可以看出,尽管立方GaN是亚稳态,高生长温度仍然有利于其晶体质量的提高.本文对GaN生长中生长温度和生长速度之间的关系作了讨论.     

利用低温插入层改善GaN外延层晶体质量研究

采用MOCVD系统在蓝宝石衬底上生长了GaN外延薄膜,在高温GaN生长中插入了低温GaN.通过改变低温GaN的生长温度和Ⅴ/Ⅲ比得到不同样品.对样品薄膜进行了高分辨X射线衍射(HRXRD)和光致发光谱(PL)测试,PL半峰宽变化不大,XRD半峰宽有明显变化.实验结果表明,低温GaN缓冲层可以使后续生长更好,达到二维生长...     

利用高频Plasma CVD在蓝宝石衬底上生长 立方GaN缓冲层及其光学性质

研究了采用高频PlasmaCVD技术在较低温度下(300—400℃)生长以GaN为基的Ⅲ-Ⅴ族氮化物的可行性,在蓝宝石衬底上生长了GaN缓冲层.热处理后的光致发光谱和X光衍射表明,生长的GaN缓冲层为立方相,带边峰位于3.15eV.在作者实验的范围内,最优化的TMGa流量为0.08sccm(TMAm=10sccm时),XPS分析结果表明此时的Ga/N比为1.03.这是第一次在高Ⅴ/Ⅲ比下得到立方GaN.相同条件下石英玻璃衬底上得到的立方GaN薄膜,黄光峰很弱,晶体质量较好.     

GaAs(001)衬底上MOCVD生长的立方相GaN外延薄膜的光学性质研究

本文报道了利用MOCVD方法,在GaAs衬底(001)面制备的立方GaN薄膜的光学性质.利用光致发光(PL)光谱的半高宽确定制备的样品具有不同的晶体质量.利用喇曼散射(RS)光谱研究了立方GaN薄膜中的光学声子模式.横向(TO)和纵向(LO)声子在立方GaN中的散射峰分别位于552cm-1和739cm-1.另外还观察到来自界面无序层的TOB和LOB.根据喇曼频移和选择定则可识别GaN中的相组成.其来自六方相GaN的E2声子模,可作为识别立方GaN中六方相的标志.随着退火温度的升高,样品中的界面层的效应减弱,六方相增加     

SiC基GaN上多晶金刚石散热膜生长及其影响

通过微波等离子体化学气相沉积(MPCVD)法,在SiC基GaN高电子迁移率晶体管(HEMT)异质结构材料上生长多晶金刚石散热膜,采用光学显微镜(OM)、拉曼光谱、非接触霍尔测试系统、X射线衍射(XRD)和扫描电子显微镜(SEM)对生长样品进行表征,研究了生长温度、多晶金刚石散热膜厚度对GaN HEMT异质结构材料性能的影响。测试结果表明,当多晶金刚石生长温度为625℃,散热膜厚度为20μm时,GaN材料载流子迁移率降低9.8%,载流子浓度上升5.3%,(002)衍射峰半高宽增加40%。生长温度越高,金刚石散热膜的生长速率越快。当金刚石散热膜厚度相差不大时,生长温度越高,GaN所受拉应力越大,材料电特性衰退越明显。多晶金刚石高温生长过程中,金刚石引入的应力未对GaN结构产生破坏作用,GaN材料中没有出现孔洞等缺陷。     

热氧化对MOCVD外延GaN薄膜光学特性影响的实验研究

采用金属有机化学气相沉积(MOCVD)法在600℃下在蓝宝石衬底上外延生长了GaN薄膜,研究了热氧化温度对GaN薄膜的微观结构和光学特性的影响.实验表明600℃生长的GaN薄膜结晶质量较差,随着热氧化温度逐渐增加,GaN薄膜的结晶质量逐渐提高,当温度提高到900℃时,GaN和Ga2O3的相共存.表面粗糙度均方根随着热氧...     

HVPE法制备GaN过程中GaAs衬底的氮化

在自制的立式氢化物气相外延(HVPE)系统炉中,一定温度下通入一定流量的NH3使GaAs(111)衬底氮化一层GaN薄膜,以防止高温外延生长GaN时GaAs分解,进而提高了之后GaN外延生长的晶体质量。实验主要通过XRD检测氮化层的质量,研究了氮化温度和时间对氮化层的影响。实验发现,氮化温度过高会使GaAs表面分解,氮化层为多晶。氮化时间过短,氮化层致密性低,不能起到保护衬底的作用;时间过长则氮化层质量降低,GaN(002)半高宽(FWHM)较大。分析结果表明,在500℃氮化2min的工艺条件下,获得的氮化层质量相比其他条件较好,致密性高。     

生长温度对InGaN/GaN多量子阱LED光学特性的影响

利用低压MOCVD系统,在蓝宝石衬底上外延生长了InGaN/GaN多量子阱蓝紫光LED结构材料.研究了生长温度对有源层InGaN/GaN多量子阱的合金组分、结晶品质及其发光特性的影响.结果表明当生长温度从730℃升到800℃时,LED的光致发光波长从490nm移到380nm,室温下PL谱发光峰的半高全宽从133meV降到73meV,表明了量子阱结晶性的提高.高温生长时,PL谱中还观察到了GaN的蓝带发光峰,说明量子阱对载流子的限制作用有所减弱.研究表明,通过改变生长温度可以对LED发光波长及有源层InGaN的晶体质量实现良好的控制.     

Si衬底GaN外延材料六角形缺陷分析

通过改变AlN形核层的生长温度分别在Si(111)衬底上生长了两个GaN样品,并对GaN外延材料表面的六角形缺陷进行了分析研究。通过显微镜和扫描电镜(SEM)观测发现,AlN形核层在高温下生长时,GaN材料表面会产生大量六角形缺陷。通过电子能谱(EDS)分析得出GaN六角形缺陷中含有大量的Si元素以及少量的Ga和Al元素,其中Si元素从Si衬底中高温扩散而来。在降低AlN形核层的生长温度后,GaN材料表面的六角形缺陷随之消失。表明AlN形核层在较低的温度下生长时可以有效地抑制Si衬底表面Si原子的扩散,减少外延层中由于衬底Si反扩散引起的缺陷。     

用侧向外延生长法降低立方相GaN中的层错密度

尝试用侧向外延(ELOG)方法来降低立方相GaN中的层错密度.侧向外延是在SiO2/GaN/GaAs图形衬底上进行的,对生长所得的立方相GaN外延层用扫描电子显微镜(SEM)和透射电子显微镜(TEM)进行了观察和分析,TEM的平面像表明经过ELOG方法生长后,立方相GaN外延层中的层错密度由侧向外延生长前的5×109cm-2降低至生长后的6×108cm-2.双晶X射线衍射(DCXRD)测量给出侧向外延前后外延层ω扫描(002)衍射摇摆曲线的半高宽(FWHM)分别为33′和17.8′,表明晶体质量有了较大改善.对立方相GaN侧向外延过程中层错减少的机制进行了讨论.     

Effects of Substrate Pretreatment Conditions on Quality of GaN Epilayer

The pure cubic GaN(c-GaN) has been grown on (001) GaAs substrates by ECR-PAMOCVD technique at low temperature using TMGa and high pure N2 as Ga and N sources,respectively.The effects of substrate pretreatment conditions on quality of cubic GaN epilayer are investigated by the measurements of TEM and XRD.It is found that hydrogen plasma cleaning,nitridation and buffer layer growth are very important for quality of cubic GaN epilayer.     

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.     

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).     

MOCVD epitaxy of InAlN on different templates

InAlN epilayers were grown on high quality GaN and A1N templates with the same growth parameters. Measurement results showed that two samples had the same In content of～16%,while the crystal quality and surface topography of the InAlN epilayer grown on the AlN template,with 282.3"（002） full width at half maximum （FWHM） of rocking curve,313.5"（102） FWHM,surface roughness of 0.39 nm and V-pit density of 2.8×10⁸ cm^-2,were better than that of the InAlN epilayer grown on the GaN template,309.3",339.1",0.593 nm and 4.2×10⁸ cm^-2.A primary conclusion was proposed that both the crystal quality and the surface topography of the InAlN epilayer grown on the AlN template were better than that of the InAlN epilayer grown on the GaN template. Therefore,the AlN template was a better choice than the GaN template for getting high quality InAlN epilayers.     

Cubic InGaN/GaN multi-quantum wells and AlGaN/GaN distributed Bragg reflectors for application in resonant cavity LEDs

In this contribution, we present results on the growth and characterization of c-InGaN/GaN MQWs and c-AlGaN/GaN DBRs, which may be used as building blocks of green (510 nm) resonant cavity light emitting diodes, which have a high potential as light sources for local area networks using plastic optical fibers. First, the impact of the indium and gallium flux on the growth of cubic-InGaN by plasma assisted molecular beam epitaxy has been studied. Indium is observed to incorporate into the c-GaInN films only when the gallium flux is reduced significantly below the value needed for stoichiometric c-GaN growth. A decrease of the surface roughness of the InGaN layers and an increase of their photoluminescence intensity per unit thickness at the transition from metal-flux limited to active nitrogen-limited growth is observed. High quality c-InGaN/GaN multi-quantum wells were grown with superlattice peaks clearly resolved in high resolution X-ray diffraction and a strong room temperature photoluminescence with a full width at half maximum of 240 meV. Cubic-AlGaN/GaN distributed Bragg reflectors with a maximum reflectivity of about 50% at 515 nm and a stop bandwidth of 33 nm have been realized. Enhanced 526 nm room temperature photoluminescence has been observed from a combined structure of a c-InGaN/GaN multi-quantum well and a c-AlGaN/GaN distributed Bragg reflector.     

GaN/GaAs(001)与GaN/Al2O3(0001)外延层光辅助湿法腐蚀行为的比较

研究了用金属有机物气相外延(MOVPE)方法在GaAs(001)衬底上生长的立方相GaN(c-GaN)外延层的光辅助湿法腐蚀特性,并和生长在蓝宝石(0001)衬底上的六方相GaN(h-GaN) 外延层的光辅助湿法腐蚀特性进行了比较.实验发现c-GaN膜的暗态电流和光电流的变化不同于h-GaN膜的腐蚀电流的变化规律.对引起上述差异的原因进行了简单的讨论.     

HVPE生长GaN厚膜的结构和光学性能

采用自制的立式HVPE设备,在GaN/蓝宝石复合衬底上生长了GaN厚外延膜,利用AFM,SEM,XRD,RBS/Channeling,CL,PL以及XPS等技术分析了厚膜的结构和光学性能.结果表明,外延层表面具有台阶结构,接近以层流生长方式二维生长,一些六角形的坑出现在膜表面,坑区具有很强的发光.腐蚀试验显示EPD仅8×106 cm-2;XRD和RBS/channeling表明GaN膜具有较好的晶体质量;PL结果也证明外延层具有高的质量,出现了尖锐的带边峰,半高宽仅67meV,同时出现了黄带和红外带,这些带的出现可能是由本征缺陷和C,O等杂质引起的.     

多缓冲层对MOCVD生长的GaN性能的影响

采用多低温缓冲层法和高低温联合缓冲层法在 MOCVD系统上生长 Ga N外延膜 .对薄膜进行了 X射线衍射和光致发光谱 (PL)测试 ,(0 0 0 2 ) X射线摇摆曲线和 PL 谱的半高宽与常规的单低温缓冲层法制备的薄膜相比均有不同程度的改善 .实验结果表明改进的缓冲层法能提高 MOCVD生长的氮化镓外延膜晶体质量