利用高频PlasmaCVD在蓝宝石衬底上生长立方GaN缓冲层及其光学性

研究了采用高频 Plasma CVD技术在较低温度下 (30 0— 40 0℃ )生长以 Ga N为基的 - 族氮化物的可行性 ,在蓝宝石衬底上生长了 Ga N缓冲层 .热处理后的光致发光谱和 X光衍射表明 ,生长的 Ga N缓冲层为立方相 ,带边峰位于 3.15 e V.在作者实验的范围内 ,最优化的 TMGa流量为 0 .0 8sccm (TMAm=10 sccm时 ) ,XPS分析结果表明此时的 Ga/ N比为 1.0 3.这是第一次在高 / 比下得到立方 Ga N.相同条件下石英玻璃衬底上得到的立方 Ga N薄膜 ,黄光峰很弱 ,晶体质量较好     

r面蓝宝石衬底上采用两步AlN缓冲层法外延生长a面GaN薄膜及应力研究

采用MOCVD技术在r面蓝宝石衬底上采用两步AlN缓冲层法外延制备了a面GaN薄膜.利用高分辨X射线衍射技术和Raman散射技术分析了样品的质量以及外延膜中的残余应力.实验结果表明:样品的(1120)面的X射线双晶摇摆曲线的半峰宽仅为0.193°,Raman光谱中E2高频模的半峰宽仅为3.9cm-1,这些说明a面GaN薄膜具有较好的晶体质量;X射线研究结果表明样品与衬底的位相关系为:[11(2)0]GaN ||[1(1)02]sapphire,[0001]Gan||[(11)01]sapphire和[(11)00]GaN[11(2)0]sapphire;高分辨X射线和Raman散射谱的残余应力研究表明,采用两步AlN缓冲层法制备的a面GaN薄膜在平面内的残余应力大小与用低温GaN缓冲层法制备的a面GaN薄膜不同,我们认为这是由引入AlN带来的晶格失配和热失配的变化引起的.     

r面蓝宝石衬底上采用两步AlN缓冲层法外延生长a面GaN薄膜及应力研究

采用MOCVD技术在r面蓝宝石衬底上采用两步AlN缓冲层法外延制备了a面GaN薄膜.利用高分辨X射线衍射技术和Raman散射技术分析了样品的质量以及外延膜中的残余应力.实验结果表明:样品的(1120)面的X射线双晶摇摆曲线的半峰宽仅为0.193°,Raman光谱中E2高频模的半峰宽仅为3.9cm-1,这些说明a面GaN薄膜具有较好的晶体质量;X射线研究结果表明样品与衬底的位相关系为:[11(2)0]GaN ||[1(1)02]sapphire,[0001]Gan||[(11)01]sapphire和[(11)00]GaN[11(2)0]sapphire;高分辨X射线和Raman散射谱的残余应力研究表明,采用两步AlN缓冲层法制备的a面GaN薄膜在平面内的残余应力大小与用低温GaN缓冲层法制备的a面GaN薄膜不同,我们认为这是由引入AlN带来的晶格失配和热失配的变化引起的.     

蓝宝石衬底上侧向外延GaN中的位错降低

采用侧向外延(ELOG)方法,在制作了条形掩膜图形的GaN衬底上用MOCVD生长高质量GaN.AFM,化学湿法腐蚀及TEM分析表明:采用两步法ELOG生长的GaN中,掩膜下方的缺陷被掩膜所阻挡,窗口区内二次生长的GaN的位错也大幅降低;在相邻生长前沿所形成的合并界面处形成晶界;化学湿法腐蚀无法得到关于合并界面处缺陷的信息.侧翼区域中极低的穿透位错使得ELOG GaN适用于在其上制作高性能的氮化物基激光器.     

图形衬底上MOCVD生长光学性质改进的GaN

An improved GaN film with low dislocation density was grown on a C-face patterned sapphire substrate （PSS） by metalorganic chemical vapor deposition （MOCVD）. The vapor phase epitaxy starts from the regions with no etched pits and then spreads laterally to form a continuous GaN film. The properties of the GaN film have been investigated by double crystal X-ray diffraction （DCXRD）, atomic force microscopy （AFM） and photoluminescence （PL）, respectively. The full-width at half-maximum （FWHM） of the X-ray diffraction curves （XRCs） for the GaN film grown on PSS in the （0002） plane and the （1012） plane are as low as 312.80 arcsec and 298.08 acrsec, respectively. The root mean square （RMS） of the GaN film grown on PSS is 0.233 nm and the intensity of the PL peak is comparatively strong.     

生长在图形化蓝宝石衬底上的GaN薄膜光学性质研究

图形化蓝宝石衬底（PSS）技术作为提高LED发光效率的方法之一,一直备受关注。研究了PSS上生长的GaN薄膜的表面形貌、吸收光谱、红外光谱、拉曼散射（Raman）和太赫兹光谱等,并与常规蓝宝石衬底上的GaN外延薄膜进行对比。结果表明,PSS上生长的GaN外延薄膜的表面形貌、光提取效率（LEE）得到明显改善。此研究成果对进一步提高GaN基短波（蓝/紫光）发光二极管（LED）的发光效率具有一定的借鉴意义,为进一步拓展PSS器件的太赫兹响应提供了依据。     

蓝宝石图形衬底上利用AlN缓冲层生长高质量GaN

在图形化衬底上以AlN作为缓冲层生长高质量的GaN薄膜,国内相关的报道较少。通过引入两步缓冲层生长方法,在蓝宝石图形衬底上生长基于AlN缓冲层的高质量GaN薄膜,利用低温AlN层生长时内部的缺陷,选择性进行腐蚀,形成衬底与外延层界面间的侧向倒斜角,提高光萃取效率;同时在其上继续生长高温AlN,为后续GaN薄膜提供高质量模板。从外延角度出发,以表面形貌及其上生长的GaN薄膜的晶体质量为衡量依据,优化了低温AlN缓冲层以及高温AlN缓冲层的生长参数,优化后LED样品在20 mA测试电流下的光输出功率较参考样品提升了4%。     

100mm直径硅衬底上MOCVD外延生长无裂纹GaN

为实现在100 mm直径硅衬底上金属有机物化学气相外延(MOCVD)生长无裂纹GaN,系统研究了预铺铝时间参数对AlN成核质量的影响、不同厚度条件下AlN层对GaN生长的影响以及Al组分渐变的AlGaN缓冲层对GaN裂纹抑制的效果。实验结果表明,适当的预铺铝时间可以显著提高AlN成核层晶体质量,合理的AlN层厚度有助于上层GaN的生长,AlN与GaN之间AlGaN缓冲层的引入可以有效抑制GaN裂纹的产生。最后,采用高分辨率X射线衍射(HRXRD)测试了MOCVD外延生长的无裂纹GaN材料,得到AlN(002)面、GaN(002)面和GaN(102)面的衍射峰半峰宽(FWHM)分别为1 382,550和746 arcsec。     

GaN缓冲层上低温生长AlN单晶薄膜

采用电子回旋共振等离子体增强金属有机物化学气相沉积(ECR-PEMOCVD)技术,在α-Al2O3(0001)(蓝宝石)衬底上,分别以高纯氮气(N2)和三甲基铝(TMAl)为氮源和铝源低温生长氮化铝(AlN)薄膜.利用反射高能电子衍射(RHEED)、原子力显微镜(AFM)和X射线衍射(XRD)等测量样品,研究了AlN缓冲层和氮化镓(GaN)对六方AlN外延层质量的影响,实验表明在GaN缓冲层上能够低温生长出C轴取向的AlN单晶薄膜.     

钯缓冲层制备GaN纳米线及光学特性分析

利用射频磁控技术,在Si衬底上以Pd为缓冲层、Ga2O3粉末作为生长GaN的Ga源,成功制备出大量GaN纳米线。通过扫描电子显微镜、透射电子显微镜和高分辨透射电子显微镜观察分析得出GaN纳米线为单晶结构,纳米线的直径为10～60nm,长度达几十个微米。X射线衍射和X射线能量散射谱显示合成的纳米线为GaN单晶结构。傅里叶变换红外吸收光谱和光致发光光谱测试表明,制得的GaN纳米线与GaN体材料相比具有不同的光学特性。     

Comparative Study on MOCVD Growth of a-Plane GaN Films on r-Plane Sapphire Substrates Using GaN, AlGaN, and AlN Buffer Layers

In this work, we have comparatively investigated the effects of the GaN, AlGaN, and AlN low-temperature buffer layers (BL) on the crystal quality of a-plane GaN thin films grown on r-plane sapphire substrates. Scanning electron microscopy images of the a-plane GaN epilayers show that using an AlGaN BL can significantly reduce the density of surface pits. The full-width at half-maximum values of the x-ray rocking curve (XRC) are 0.19°, 0.36°, and 0.48° for the films grown using Al_0.15Ga_0.85N, GaN, and AlN BLs, respectively, indicating that an AlGaN BL can effectively reduce the mosaicity of the films. Room-temperature photoluminescence shows that the AlGaN BL results in lower impurity incorporation in the subsequent a-plane GaN films, as compared with the case of GaN and AlN BLs. The higher crystal quality of a-plane GaN films produced by the Al_0.15Ga_0.85N BL could be due to improvement of BL quality by reducing the lattice mismatch between the BL and r-sapphire substrates, while still keeping the lattice mismatch between the BL and epitaxial a-plane GaN films relatively small.     

Growth of GaN on Buffer Layers with Different Polarities by Hydride Vapor-Phase Epitaxy

This paper reports the properties of GaN grown by the hydride vapor-phase epitaxy (HVPE) technique on buffer layers with different polarities. The N-, mixed-, and Ga-polarity buffer layers were grown by molecular-beam epitaxy (MBE) on sapphire (0001) substrates; then, thicker GaN epilayers were grown on these by HVPE. The surface morphology, structural, and optical properties of these HVPE-GaN epilayers were characterized by atomic force microscopy (AFM), x-ray diffraction (XRD), scanning electron microscopy, and photoluminescence (PL) spectroscopy. The results indicate that the crystallinity of these HVPE-GaN epilayers depends on the polarity of the buffer layer.     

Optical Properties of Silicon—doped InGaN and GaN Layers

The optical properties of Silicon—doped InGaN and GaN grown on sapphire by MOCVD have been investigated by photoluminescence (PL) method. At room temperature, the band—gap peak of InGaN is 437.0 nm and its full width of half—maximum (FWHM) is about 14.3 nm. The band—gap peak and FWHM for GaN are 364.4 nm and 9.5 nm, respectively. By changing the temperature from 20 K to 293 K, it is found that the PL intensity of samples decreases but the FWHM broadens with the increasing of the temperature.GaN sample shows red—shift, InGaN sample shows red—blue—red—shift. The temperature dependence of peak energy shift is studied and explained.     

掺硅InGaN和掺硅GaN的光学性质的研究

采用光致发光方法研究了采用金属有机化学气相沉积(MOCVD)在蓝宝石衬底上生长的掺硅InGaN和掺硅CaN材料的光学性质。在室温下．InGaN材料带边峰位置为437．0nm，半高宽为14．3nm；GaN材料带边峰位置为363．4nm．半高宽为9．5nm。进行变温测量发现．随温度的升高．两种材料的发光强度降低，半高宽增大；GaN材料的带边峰值能量位置出现红移现象．与Varshini公式符合较好；InGaN材料的带边峰值能量位置则出现红移-蓝移-红移现象．这与InGaN材料的局域态、热效应以及由于电子-空穴对的形成而造成的无序程度增加有关．对大于140K的峰值能量位置的红移用Varshini公式拟合．符合较好。     

Characterization of GaN Buffer Layers and Its Epitaxial Layers Grown by MOCVD

Low-pressure MOCVD has been used to investigate the properties of low-temperature buffer layer depodition conditions and their influence on the properties of high-temperature GaN epilayers grown subsequently.It is found that the surface morphology of the as-grown buffer layer after thermal annealing at 1030℃and 1050℃ depends strongly on the thickness of the buffer layer.In particular when a thick buffer layer is used, large trapezoidal nuclei are formed after annealing.     

Characteristics of MBE-Grown GaN Detectors on Double Buffer Layers Under High-Power Ultraviolet Optical Irradiation

In this paper, present experimental investigations on the radiation hardness of GaN-based Schottky diode photodetectors. High-power ultraviolet (UV) radiation obtained from a Xenon lamp is used as the light source for the optical-stressing experiment. Two types of devices are being investigated. One has a double-buffer-layer structure that consists of a conventional high-temperature AlN buffer layer and an intermediate temperature buffer layer (type I), and the control device was fabricated with only a conventional AlN buffer layer (type II). Detailed current-voltage, capacitance-voltage, flicker noise, and responsivity measurements performed on the detectors show that the degradations of the devices arose from the defects present at the Schottky junctions due to the exposure of the devices to the high-power UV radiation. Both types of devices exhibit degradation in their optoelectronic properties. However, type-I devices, in general, exhibit gradual and slow degradation, whereas type-II devices exhibit catastrophic breakdowns in the device characteristics. The experimental data indicate significant improvement in the radiation hardness for type-I devices