氢化物气相外延生长的GaN膜中的应力分析

对在c面蓝宝石上用氢化物气相外延法(HVPE)生长的六方相纤锌矿结构的GaN膜中的应力进行了分析。高分辨X射线衍射(002)面和(102)面摇摆曲线扫描(半高宽数值分别为317和358角秒)表明生长的GaN膜具有较好的晶体质量。利用高分辨X射线衍射技术准确测量了制备的GaN膜的晶格常数,并计算得到GaN膜中面内双轴应变和面外双轴应变分别为3.37×10-4和-8.52×10-4,等静压应变为-7.61×10-5。拉曼光谱和激光光致发光谱测试表明HVPE-GaN外延膜具有较好的光学特性,利用拉曼光谱的E₂模式特征峰和激光光致发光谱中近带边发射峰的频移定量计算了外延膜中的面内双轴压应力和等静压应力。两种方法得到的面内双轴压应力较为相符。     

AlN插入层对硅衬底GaN薄膜生长的影响

利用金属有机化合物气相外延沉积技术在2inch(5.08cm)Si(111)图形衬底上生长了GaN外延薄膜,在Al组分渐变AlGaN缓冲层与GaN成核层之间引入了AlN插入层,研究了AlN插入层对GaN薄膜生长的影响。结果表明,随着AlN插入层厚度的增加,GaN外延膜(002)面与(102)面X射线衍射摇摆曲线半峰全宽明显变小,晶体质量变好,同时外延膜在放置过程中所产生的裂纹密度逐渐减小直至不产生裂纹。原因在于AlN插入层的厚度对GaN成核层的生长模式有明显影响,较厚的AlN插入层使GaN成核层倾向于岛状生长,造成后续生长的nGaN外延膜具有更多的侧向外延成分,从而降低了GaN外延膜中的位错密度,减少了GaN外延膜中的残余张应力。同时还提出了一种利用荧光显微镜观察黄带发光形貌来表征GaN成核层形貌和生长模式的新方法。     

图形衬底量子线生长制备与荧光特性研究

报道了在V型槽图形衬底上利用分子束外延技术外延生长的GaAs/AlGaAs量子线.外延截面在扫描电子显微镜下可以看到在V型槽底部形成了弯月型量子线结构,量子线尺寸约为底边60 nm高14 nm的近三角形.低温87 K下光致发光谱测试在793.7和799.5 nm处出现峰值,验证了量子线的存在.理论近似计算结果显示,相比等宽度量子阱有8 meV的蓝移正是由于横向量子限制引起的. 关键词： V型槽图形衬底 量子线 GaAs     

N极性GaN薄膜的MOCVD外延生长

采用MOCVD技术在c面蓝宝石衬底上外延制备了N极性GaN薄膜。通过KOH腐蚀的方法判定了GaN外延薄膜的极性。通过X射线双晶衍射(XRD)摇摆曲线和光致荧光(PL)谱测试研究了成核层生长时间对N极性GaN薄膜晶体质量和发光性能的影响。研究结果表明,成核层生长时间为300 s时,N极性GaN薄膜样品的位错密度最低,发光性能最好。采用拉曼(Raman)光谱对样品的应变状态进行了分析。     

金属有机物化学气相沉积同质外延GaN薄膜表面形貌的改善

为了获得高质量的GaN薄膜材料,研究了金属有机物气相沉积系统中GaN插入层对GaN衬底同质外延层表面宏观缺陷和晶体质量的影响.研究发现,插入层生长温度是影响GaN同质外延膜表面形貌和晶体质量的关键因素.由于生长模式与插入层生长温度相关,随着插入层生长温度的降低,外延膜生长模式由准台阶流模式转变为层状模式,GaN同质外延膜表面丘壑状宏观缺陷逐渐减少,但微观位错密度逐渐增大.通过对插入层温度和厚度的优化,进一步调控外延层的生长模式,最终有效降低了外延层表面的宏观缺陷,获得了表面原子级光滑平整、位错密度极低的GaN同质外延膜,其X射线衍射摇摆曲线(002),(102)晶面半峰宽分别为125arcsec和85arcsec,表面粗糙度均方根大小为0.23nm.     

Si(111)衬底上GaN的MOCVD生长

利用LP-MOCVD在Si（111）衬底上,以高温AIN为缓冲层,分别用低温GaN（LT-GaN）和偏离化学计量比富Ga高温GaN（HT-GaN）为过渡层外延生长六方相GaN薄膜。采用高分辨率双晶X射线衍射（DCXRD）,扫描电子显微镜（SEM）,原子力显微镜（AFM）和室温光致荧光光谱（RT-PL）进行分析。结果表明,有偏离化学计量比富Ga HT-GaN为过渡层生长的GaN薄膜质量和光致荧光特性均明显优于以LT-GaN为过渡层生长的GaN薄膜,得到GaN（0002）和（1012）的DCXRD峰,其半峰全宽（FWHM）分别为698s和842s,室温下的光致荧光光谱在361nm处有一个很强的发光峰,其半峰全宽为44．3meV。     

磁控反应溅射AlN缓冲层对GaN基LED器件性能的影响

以直流磁控反应溅射法(RMS)在图形化蓝宝石衬底上制备的AlN薄膜作为缓冲层,采用金属有机化学气相沉积法(MOCVD)外延生长了GaN基LED。与MOCVD生长的低温GaN缓冲层相比,RMS制备的AlN缓冲层具有表面更平整、颗粒更小的形核岛,有利于促进GaN外延的横向生长,减少了形核岛合并时的界面数量和高度差异,降低了缺陷和位错产生的几率。研究结果表明,溅射AlN缓冲层取代传统低温GaN缓冲层后,外延生长的GaN材料具有更高的晶体质量,LED器件在亮度、漏电和抗静电能力等光电特性上均有明显提升。     

使用SiNx原位淀积方法生长的GaN外延膜中的应力研究

采用低压MOCVD系统，在生长过程中使用SiN_x原位淀积的方法产生纳米掩模，并 在纳米掩模上进行选区生长和侧向外延制备了GaN外延薄膜.使用拉曼光谱和光荧光的手段对 GaN外延膜中的残余应力进行了研究.研究发现，用SiN_x原位淀积出纳米掩模后 ，GaN生长将由二维向三维转变，直到完全合并为止.利用拉曼光谱和光荧光谱分别研究了薄 膜中的残余应力，两者符合得很好；这种方法生长出的GaN薄膜的应力分布较传统的侧向外 延更加均匀；并且从中发现随着生长过程中SiN_x原位淀积时间的增加，生长在 其上的GaN外延膜中的残余应力减小.这是因为，随着SiN_x原位淀积时间的增加 ，SiN_x纳米掩模的覆盖度也增大.因此侧向外延区的比例增大，残余应力随之减 小. 关键词： GaN x原位淀积')" href="#">SiN_x原位淀积 拉曼 光荧光 残余应力     

AlGaN插入层对6H-SiC上金属有机物气相外延生长的GaN薄膜残余应力及表面形貌的影响

研究了具有不同台阶数目的AlGaN插入层对在6H-SiC衬底上利用金属有机物气相外延（MOVPE）生长的GaN体材料残余应力和表面形貌的影响.高分辨率X射线衍射测试表明样品的c轴晶格常数随台阶数目的增多而增大;低温光荧光谱中GaN发光峰也随着台阶数目增多而发生蓝移,这些变化都反映出GaN中残余张应力的减小.此外,原子力显微镜测试表明样品表面起伏和粗糙度也都随着插入层的引入和台阶数目的增多得到了明显的改善. 关键词： 残余应力 表面形貌 SiC衬底 AlGaN插入层     

AlN插入层对a-AlGaN的外延生长的影响

采用有机金属化学气相沉积(MOCVD)在r面蓝宝石衬底上生长a-AlGaN外延膜,研究了AlN插入层对a-AlGaN外延膜的应力和光学性质的影响。根据高分辨X射线衍射(HRXRD)技术和扫描电子显微镜(SEM)我们可以得到,AlN插入层有效地提高了a-AlGaN外延膜的晶体质量并减小了外延膜材料结构的各向异性。由拉曼光谱得到AlN插入层的引入减小了a-AlGaN外延膜的面内压应力,其原因是AlN插入层可以当作衬底有效的调制与减小a-AlGaN外延膜与r面蓝宝石衬底的晶格失配,从而使a-AlGaN的面内应力得到适当释放。对室温下的光致发光进行测量得到AlN插入层的使用使近带边发射峰(NBE)发生了红移,这可能是由于残余应力的减小引起。     

界面形核时间对GaN薄膜晶体质量的影响

利用金属有机化学气相沉积技术系统研究了界面形核时间对c面蓝宝石衬底上外延生长GaN薄膜晶体质量的影响机理. 用原子力显微镜、扫描电子显微镜、高分辨X射线衍射仪以及光致发光光谱仪表征材料的晶体质量以及光学性质. 随着形核时间的延长, 退火后形成的形核岛密度减小、尺寸增大、均匀性变差, 使得形核岛合并过程中产生的界面数量先减小后增大, 导致GaN外延层的螺位错和刃位错密度先减小后增大, 这与室温光致发光光谱中得到的带边发光峰与黄带发光峰的比值先增大后降低一致. 研究结果表明, 外延生长过程中, 界面形核时间会对GaN薄膜中的位错演变施加巨大影响, 从而导致GaN外延层的晶体质量以及光学性质的差异.     

Structural and optical properties of an InxGa1−xN/GaN nanostructure

The structural and optical properties of an In_xGa_1−xN/GaN multi-quantum well (MQW) were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE) and photoluminescence (PL). The MQW structure was grown on c-plane (0 0 0 1)-faced sapphire substrates in a low pressure metalorganic chemical vapor deposition (MOCVD) reactor. The room temperature photoluminescence spectrum exhibited a blue emission at 2.84 eV and a much weaker and broader yellow emission band with a maximum at about 2.30 eV. In addition, the optical gaps and the In concentration of the structure were estimated by direct interpretation of the pseudo-dielectric function spectrum. It was found that the crystal quality of the InGaN epilayer is strongly related with the Si doped GaN layer grown at a high temperature of 1090 °C. The experimental results show that the growth MQW on the high-temperature (HT) GaN buffer layer on the GaN nucleation layer (NL) can be designated as a method that provides a high performance InGaN blue light-emitting diode (LED) structure.     

Influence of growth parameters on the properties of InGaN/GaN multiple quantum well grown by metalorganic chemical vapor deposition

The effects of growth parameters such as barrier growth time, growth pressure and indium flow rate on the properties of InGaN/GaN multiple quantum wells (MQWs) were investigated by using photoluminescence (PL), high resolution X-ray diffraction (HRXRD), and atomic force microscope (AFM). The InGaN/GaN MQW structures were grown on c-plane sapphire substrate by using metalorganic chemical vapor deposition. With increasing barrier growth time, the PL peak energy is blue-shifted by 18 nm. For InGaN/GaN MQW structures grown at different growth pressures, the PL intensity is maximized in the 300 Torr – grown structure, which could be attributed to the improved structural quality confirmed by HRXRD and AFM results. Also, the optical properties of InGaN/GaN MQW are strongly affected by the indium flow rate.     

New design of nozzle structures and its effect on the surface and crystal qualities of thick GaN using a horizontal HVPE reactor

High-quality thick GaN films without cracks were achieved by using a new nozzle structure in the reactor grown by the hydride vapor phase epitaxy on sapphire substrates. Optical contrast microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray double diffraction (XRD) and cathodoluminescence (CL) were carried out to reveal the surface, crystal and optical properties of the GaN epilayer. It was found that the nozzle structure in the reactor has a large effect on the growth rate, surface flat, crystal quality, and the uniformity of the growth. Compared with the old one, the new nozzle structure (denoted as multi-layers nozzle) can improve dramatically the properties of thick GaN. Mirror, colorless and flat GaN thick film was obtained and its (0 0 0 2) FWHM results were reduced from 1000 to 300 arcsec when the new nozzle was used. AFM result revealed a step flow growth mode for GaN layer with the new nozzle. Room-temperature CL spectra on the GaN films showed a strong near-band-edge peak for the new nozzle, but there is only weak emitting peak for the old nozzle. New nozzle structure can improve the uniform of flow field near the surface of substrates compared with the old one, which leads to the improvement of properties of GaN thick film by hydride vapor phase epitaxy (HVPE).     

High resolution X-ray diffraction of GaN grown on Si (1 1 1) by MOVPE

High temperature GaN layers have been grown on Si (1 1 1) substrate by metalorganic vapor phase epitaxy (MOVPE). AlN was used as a buffer layer and studied as a function of thickness and growth temperature. The growth was monitored by in situ laser reflectometry. High resolution X-ray diffraction (HRXRD) revealed that optimized monocrystalline GaN was obtained for a 40 nm AlN grown at 1080 °C. This is in good agreement with the results of morphological study by scanning electron microscopy (SEM) and also confirmed by atomic force microscopy (AFM) observations. The best morphology of AlN with columnar structure and lower rms surface roughness is greatly advantageous to the coalescence of the GaN epilayer. Symmetric and asymmetric GaN reflections were combined for twist and stress measurements in monocrystalline GaN. It was found that mosaicity and biaxial tensile stress are still high in 1.7 μm GaN. Curvature radius measurement was also done and correlated to the cracks observations over the GaN surface.     

InGaN/GaN多量子阱的组分确定和晶格常数计算

采用金属有机化学气相沉积(MOCVD)技术以蓝宝石为衬底在n型GaN单晶层上生长了InGaN/GaN多量子阱结构外延薄膜，利用高分辨X射线衍射(HRXRD)，卢瑟福背散射/沟道(RBS/channeling)，以及光致发光(PL)技术对InGaN/GaN多量子阱结构薄膜分别进行了平均晶格常数计算、In原子替位率计算和In组分的定量分析.研究表明：InGaN/GaN多量子阱的水平和垂直方向平均晶格常数分别为a_epi=0.3195nm，c_epi=0.5198nm，In原子的替位率为99.3%，利用HRXRD和RBS/channeling两种分析技术计算In的组分分别是0.023和0.026，并与样品生长时设定的预期目标相符合，验证了两种实验方法的准确性；而用室温条件下的光致发光谱(PL)来计算InGaN/GaN多量子阱中In的组分是与HRXRD和RBS/channeling的实验结果相差很大，说明用PL测试In组分的方法是不适宜的. 关键词： InGaN/GaN多量子阱 高分辨X射线衍射 卢瑟福背散射/沟道 光致发光     

三甲基镓流量对GaN外延层和GaN缓冲层生长的影响

采用金属有机物气相外延法在蓝宝石衬底上生长了以GaN为缓冲层的GaN薄膜.研究了不同三甲基镓流量下所生长缓冲层对GaN外延层质量的影响.对样品采用X线双晶衍射法测试其结晶质量,光致发光法测试其光学特性.实验结果显示高三甲基镓流量下生长的缓冲层可以提高GaN外延层的质量.对缓冲层进行的原子力显微镜测试分析表明不同三甲基镓流量会显著地影响缓冲层的生长模式.根据试验结果构造了一个GaN缓冲层的生长模型.     

Optical and structural investigation of a-plane GaN layers on r-plane sapphire with nucleation layer optimization

Nonpolar a-plane GaN epilayers are grown on several r-plane sapphire substrates by metal organic chemical vapour deposition using different nucleation layers:(A) a GaN nucleation layer deposited at low temperature(LT);(B) an AlN nucleation layer deposited at high temperature;or(C) an LT thin AlN nucleation layer with an AlN layer and an AlN/AlGaN superlattice both subsequently deposited at high temperature.The samples have been characterized by Xray diffraction(XRD),atomic force microscopy and photoluminescence.The GaN layers grown using nucleation layers B and C show narrower XRD rocking curves than that using nucleation layer A,indicating a reduction in crystal defect density.Furthermore,the GaN layer grown using nucleation layer C exhibits a surface morphology with triangular defect pits eliminated completely.The improved optical property,corresponding to the enhanced crystal quality,is also confirmed by temperature-dependent and excitation power-dependent photoluminescence measurements.     

Characteristics of GaN epilayer grown on Al2O3 with AlN buffer layer by molecular beam epitaxy

Double crystal rocking curve (DCRC), atomic force microscopy (AFM), scanning electron microscopy (SEM), and photoluminescence (PL) measurements on GaN epilayers grown with various thicknesses (3.4, 8.5, 17, 34, and 51 nm) of the AlN buffer layer were carried out to investigate the surface, the structural, and the optical properties of the GaN epilayers. The results of the DCRC, AFM, SEM, and PL measurements showed that the GaN epilayer grown on a 3.4 nm AlN buffer layer had the best quality. These results indicate that GaN active layers grown on 3.4 nm AlN buffer layers hold promise for potential applications in optoelectronic devices.