一种外延生长高质量GaN薄膜的新方法

采用化学方法腐蚀c-面蓝宝石衬底，以形成一定的图案；利用LP-MOCVD在经过表面处理的蓝宝石衬底上以及常规c-面蓝宝石衬底上外延生长GaN薄膜.采用高分辨率双晶X射线衍射(DCXRD)、三维视频光学显微镜(OM)、扫描电子显微镜(SEM)和原子力显微镜(AFM)进行分析，结果表明，在经过表面处理形成一定图案的蓝宝石衬底上外延生长的GaN薄膜明显优于在常规蓝宝石衬底上外延生长的GaN薄膜，其(0002)面上的XRD FWHM为208.80弧秒，(1012)面上的为320.76弧秒.同时，此方法也克服了传统 关键词： 表面处理 MOCVD 横向外延生长 GaN薄膜     

蓝宝石表面处理对氮化镓薄膜的影响

采用化学方法腐蚀c-面蓝宝石衬底，以形成一定的图案；利用LP-MOCVD在经过不同腐蚀时间的蓝宝石衬底上外延生长GaN薄膜。采用高分辨率双晶X射线衍射（DCXRD）、三维视频光学显微镜（OM）、扫描电子显微镜（SEM）和原子力显微镜（AFM）进行分析。结果表明，对蓝宝石衬底腐蚀50min情况下，外延生长的GaN薄膜晶体质量最优，其（0002）面上的XRD 半峰全宽为202.68arcsec，（10-12）面上的XRD 半峰全宽为300.24arcsec；其均方根粗糙度（RMS）为0.184nm。     

斜切蓝宝石衬底MOCVD生长GaN薄膜的透射电镜研究

利用MOCVD技术在斜切角度为0.3°的c面蓝宝石衬底上生长了非故意掺杂 GaN 薄膜, 并采用透射电子显微镜对材料的质量和材料内部缺陷进行了分析. 研究发现斜切蓝宝石衬底上外延的GaN材料中,位错在距离衬底0.8 μm附近大量湮灭, 同时位错扎堆出现.基于上述现象, 提出了斜切衬底上GaN材料中位错的湮灭机制, 解释了斜切衬底能够提高GaN晶体质量的原因.     

腐蚀时间对蓝宝石衬底上外延生长GaN质量的影响

使用熔融的KOH在高温下对c面蓝宝石衬底进行不同时间的腐蚀,借助扫描电镜、原子力显微镜对衬底表面进行了表征,然后利用金属有机物化学气相沉积设备在不同腐蚀时间的衬底样品上进行了GaN材料的外延生长。通过X射线衍射结果比较了两组衬底上外延材料的质量,利用原子力显微镜结果对外延层表面形貌进行了分析,最后论述了腐蚀时间的调整对蓝宝石衬底上外延生长氮化镓质量的影响机理。     

Ga2O3/GaN/蓝宝石模板上β-Ga2O3薄膜的生长

为获得高质量的β-Ga2O3薄膜,将c面蓝宝石上生长的GaN薄膜进行高温氧化制成了Ga2O3/GaN/蓝宝石模板,进而在模板上利用金属有机化学气相沉积(MOCVD)工艺进行了β-Ga2O3薄膜的同质外延。通过X射线衍射仪、原子力显微镜、场发射扫描电子显微镜等方法对样品的晶体结构、表面形貌等性质进行测试与分析。结果表明,该方法获得的β-Ga2O3薄膜晶体质量受GaN薄膜氧化效果与MOCVD工艺条件等因素影响较大。通过优化实验条件,得到了质量较高的β-Ga2O3薄膜。与蓝宝石上或GaN薄膜上异质外延得到的β-Ga2O3薄膜相比,薄膜的晶体质量明显提高。通过对比不同样品的晶体质量、表面形貌和制备过程,发现该方法成功地将β-Ga2O3薄膜在蓝宝石衬底或GaN/蓝宝石模板上异质外延转化为了Ga2O3/GaN/蓝宝石模板上的同质外延,有效地减小了β-Ga2O3薄膜和蓝宝石、GaN之间较大的晶格失配和热失配,有利于提高β-Ga2O3薄膜的晶体质量。     

基于透射谱的GaN薄膜厚度测量

通过对蓝宝石衬底异质外延GaN薄膜光学透射谱的分析，结合晶体薄膜的干涉效应原理并考虑折射率随光子波长变化的影响，从理论上推导出了实用的薄膜厚度计算方法. 实际应用表明，该方法是一种快速准确的GaN薄膜厚度测量方法. 关键词： GaN 透射谱 厚度测量     

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。     

GaN载流子浓度和迁移率的光谱研究

用红外反射光谱的方法对生长在蓝宝石衬底上的α-GaN外延薄膜的载流子浓度和迁移率进行了研究.通过测量蓝宝石衬底和不同Si掺杂浓度的一系列GaN外延膜的远红外反射谱并进行理论计算和拟合,得到GaN中的声子振动参量和等离子振荡的频率及阻尼常量,并由此计算得到其载流子浓度和迁移率.计算结果,红外方法得到的载流子浓度与Hall测量相一致,但迁移率比Hall迁移率要低约二分之一.同时红外谱与喇曼谱上明显观察到LO声子与等离子体激元耦合模,(LPP)随掺杂浓度的变化. 关键词： α-GaN外延薄膜 红外反射光谱 载流子浓度 迁移率 LO声子与等离子体激元耦合模 Raman光谱     

SiO2图形化蓝宝石衬底对GaN生长及LED发光性能的影响

为了提高氮化镓(GaN)基发光二极管(LEDs)的发光性能,采用等离子体增强化学气相沉积(PECVD)在蓝宝石衬底上沉积SiO_2薄膜,经过光刻和干法刻蚀技术制备了SiO_2图形化蓝宝石衬底(SiO_2 patterned sapphire substrate, SPSS),利用LED器件的外延生长和微纳加工技术获得了基于SPSS的GaN基LED器件。通过分析GaN外延层晶体质量、光提取效率和LED器件性能,重点研究了SPSS对GaN生长及LED发光性能的影响。实验及模拟仿真结果表明,与常规图形化蓝宝石衬底(Conventional patterned sapphire substrate, CPSS)相比,SPSS上生长的GaN外延层位错密度较低,晶体质量较高,SPSS-LED的光提取效率提高26%、光输出功率和亮度均提高约5%。     

用MOVPE和RF-MBE方法极性控制生长GaN

本文报道了用低压MOVPE和RF-分子束外延法在蓝宝石衬底上作极性控制的GaN生长.以“双Al单层”模型讨论了用MOVPE和MBE法在蓝宝石衬底上生长GaN的极性选择的机理,并对AlN在极性转换过程中的作用给出了适当的解释.通过极性控制的生长,使MBE法生长的GaN的表面形貌和电学特性都得到了改善;并对LP-MOVPE生长开发出了一种“三步生长法”,这样就可以用更多的外延方式在蓝宝石衬底上生长出高质量的GaN膜.     

淀积在不同小倾角蓝宝石衬底的n型GaN的研究

采用金属有机物化学淀积技术在不同倾角（0°—03°）的蓝宝石衬底上外延n型GaN.通过原子力显微镜观察到n型GaN均呈台阶流生长模式,02°和03°倾角衬底的n型GaN表面台阶朝向相同、分布均匀,明显地看到在0°倾角衬底的n型GaN表面由台阶重构直接导致的台阶朝向随机分布、疏密不匀的形貌.电子背散射分析表明,在0°倾角衬底的n型GaN外延层的应力随外延厚度增加而增加,而02°和03°倾角衬底的n型GaN外延层的应力没有明显的变化.电学和光学特性研究表明,02°和03°倾角衬底的n型GaN有较高的电子浓度和较低的黄光带与近带边强度之比. 关键词： 金属有机物化学淀积 氮化物 原子力显微镜 光致发光     

Effect of double AlN buffer layer on the qualities of GaN films grown by radio-frequency molecular beam epitaxy

This paper reports that the GaN thin films with Ga-polarity and high quality were grown by radio-frequency molecular beam epitaxy on sapphire （0001） substrate with a double A1N buffer layer. The buffer layer consists of a high-temperature （HT） A1N layer and a low-temperature （LT） A1N layer grown at 800℃ and 600℃, respectively. It is demonstrated that the HT-A1N layer can result in the growth of GaN epilayer in Ga-polarity and the LT-A1N layer is helpful for the improvement of the epilayer quality. It is observed that the carrier mobility of the GaN epilayer increases from 458 to 858cm^2/V.s at room temperature when the thickness of LT-A1N layer varies from 0 to 20nm. The full width at half maximum of x-ray rocking curves also demonstrates a substantial improvement in the quality of GaN epilavers by the utilization of LT-A1N layer.     

The influence of AlN/GaN superlattice intermediate layer on the properties of GaN grown on Si（111） substrates

AlN/GaN superlattice buffer is inserted between GaN epitaxial layer and Si substrate before epitaxial growth of GaN layer. High-quality and crack-free GaN epitaxial layers can be obtained by inserting AlN/GaN superlattice buffer layer. The influence of AlN/GaN superlattice buffer layer on the properties of GaN films are investigated in this paper. One of the important roles of the superlattice is to release tensile strain between Si substrate and epilayer. Raman spectra show a substantial decrease of in-plane tensile strain in GaN layers by using AlN/GaN superlattice buffer layer. Moreover, TEM cross-sectional images show that the densities of both screw and edge dislocations are significantly reduced. The GaN films grown on Si with the superlattice buffer also have better surface morphology and optical properties.     

Thickness measurement of GaN epilayer using high resolution X-ray diffraction technique

In this paper we propose a new method for measuring the thickness of the GaN epilayer, by using the ratio of the integrated intensity of the GaN epilayer X-ray diffraction peaks to that of the sapphire substrate ones. This ratio shows a linear dependence on the GaN epilayer thickness up to 2 μm. The new method is more accurate and convenient than those of using the relationship between the integrated intensity of GaN epilayer diffraction peaks and the GaN thickness. Besides, it can eliminate the absorption effect of the GaN epilayer.     

The effect of low temperature AlN interlayers on the growth of GaN epilayer on Si (111) by MOCVD

Low temperature (LT) AlN interlayers were used to effectively reduce the tension stress and micro-cracks on the surface of the GaN epilayer grown on Si (111) substrate. Optical Microscopy (OM), Atomic Force Microscopy (AFM), Surface Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were employed to characterize these samples grown by metal-organic chemical vapor deposition (MOCVD). In addition, wet etching method was used to evaluate the defect of the GaN epilayer. The results demonstrate that the morphology and crystalline properties of the GaN epilayer strongly depend on the thickness, interlayer number and growth temperature of the LT AlN interlayer. With the optimized LT AlN interlayer structures, high quality GaN epilayers with a low crack density can be obtained.     

Temperature effects on optical properties of InN thin films

Transmission measurements have been carried out on InN thin films grown by radio frequency magnetron sputtering on a sapphire (0001) substrate at 10–300 K. With the aid of a novel procedure developed for analyzing the transmission spectra, the effect of temperature on optical properties, such as the absorption coefficient, band-gap, Urbach bandtail characteristics, refractive index and extinction coefficient, of InN thin films has been determined. The wavelength and temperature dependence of the absorption coefficient in both the Urbach and intrinsic absorption regions has been described by a series of empirical formulae. The temperature dependence of the refractive index dispersion below the band-gap is also found to follow a Sellmeier equation. These formulae are very useful for the characterization and device design of InN films. The free-electron concentration in the InN thin film determined here is also found to be in good agreement with that obtained from infrared reflection measurements. PACS 78.66.Fd; 78.40.Fy; 78.20.Bh; 78.20.Ci