Ⅲ族氮化物外延层中的缺陷

采用光荧光和阴极荧光方法 ,对 Ga N外延层中的黄色和蓝色发光进行测量分析 ;同时 ,采用原子力显微镜、扫描电镜及其能谱测量外延层中的缺陷。结果表明 ,黄色和蓝色发光与残留杂质有关。采用第一原理计算结果显示 ,残留 C、O杂质、本征缺陷等是黄色和蓝色的可能物理起源。采用原子力显微镜、扫描电镜、透射电镜及其能谱对 Ga N/Al Ga N异质结中的纳米管进行观测 ,了解了纳米管的形貌。结果表明 ,构成纳米管的小面可能是外延过程中表面吸附引起的 ;计算结果显示 ,纳米管形貌变化与 Ga N/Al Ga N界面处晶格失配应力有关。采用透射电镜观察外延层中沉积物及其周围位错的结构表明 ,沉积物附近应力的存在是位错产生的主要原因     

SiC单晶的生长及其器件研制进展

ＳｉＣ具有禁带宽度大，热导率高，电子的饱和漂移速度大，临界击穿电场高和介电常数低等特点，在高频大功率，耐高温，抗辐照的半导体器件及紫外探测器和短波发光二极管方面具有广泛的应用前景，本文综述了半导体ＳｉＣ体单晶和薄膜的生长及其器件研制的概况。     

SOLAR CELLS IN THIN EPITAXIAL LAYERS ON METALLURGICAL SILICON SUBSTRATES

Conversion efficiencies of 11.5-12% have been obtained for solar cells with an active layer epitaxially grown on upgraded metallurgical grade silicon substrates made by industry. An epilayer thickness of 30 μm was shown to be sufficient if the substrate doping is much larger than the epilayer doping. Spectral response measurements, fitted to simple models, showed that:

? the electron diffusion length reached 120 μm in the epilayer,

? a back surface field was efficient in increasing collection efficiency,

? Optical path enhancement due to texturisation decreased absorption losses.

These results were confirmed by modeling of the short circuit current and open circuit voltage of the cells.

Economic viability is discussed. The results can also be used to increase the efficiency of conventional solar cells built on thin wafers (< 150μm).     

Improved GaN grown on Si(111) substrate using ammonia flow modulation on SiNx mask layer by MOCVD

In this paper, 1 μm n-GaN was grown by using varied and fixed ammonia flow (NH₃) on SiN _x mask layer on Si(111) substrate using metal organic chemical vapor deposition (MOCVD). In-situ optical reflectivity traces of GaN growth show that the three- to two-dimensional process has been prolonged by using varied ammonia flow on SiN _x mask layer method compared with that grown by fixing ammonia flow. Structural and optical properties were characterized by high-resolution X-ray diffraction and photoluminescence, and compared with the sample grown by fixing ammonia flow, GaN grown using the varied ammonia flow on SiNx mask layer showed better structure and optical quality. It was assumed that the low NH₃ flow in the initial growth stage considerably increased the GaN island density on the nano-porous SiN _x layer by enhancing vertical growth. Lateral growth was significantly favored by high NH₃ flow in the subsequent step. As a result, the improved crystal and optical quality was achieved utilizing NH₃ flow modulation for GaN buffer growth on Si(111) substrate.     

一种碳化硅外延层质量评估新技术

由于当前多种技术同时被用于碳化硅(SiC)外延层质量表征,造成外延层和器件研制成本高、时间长、易损伤、不能在线检测等,限制了SiC外延材料和器件的发展.用红外镜面反射谱、拉曼散射谱、X射线衍射、原子力显微镜和X射线光电子能谱等对4H-SiC外延层质量进行了测试.测试结果的分析和比较表明,红外镜面反射谱不但能提供拉曼散射谱、X射线衍射、原子力显微镜和X射线光电子能谱等测试的所有质量参数,而且其解析结果与其他几种技术的解析结果一致.因此,红外镜面反射谱可以作为一种低成本、快捷、无损、可在线的碳化硅外延层质量监测技术.     

红外透射光谱在HgCdTe外延薄膜性能评价中的应用

用最新发表的ＨｇＣｄＴｅ材料的光学常数对ＭＢＥ工艺生长的ＨｇＣｄＴｅ／ＣｄＴｅ／ＧａＡｓ材料的透射光谱进行了理论计算，对受生长工艺破坏的衬底背面再次进行抛光处理，消除因表面不平整引起的漫反射效应，使实验测量得到的光谱曲线与理论计算结果很好地吻合，由此得到的ＨｇＣｄＴｅ和ＣｄＴｅ外延层的厚度和解理面上用显微镜测量的数值相同。     

Dislocation-free undoped semi-insulating GaAs epilayers prepared by chloride chemical vapor deposition and successive wafer annealing

Dislocation-free (DF) undoped semi-insulating GaAs epilayers have been realized by chloride chemical vapor deposition and successive wafer annealing. It was found that undoped conductive DF GaAs epilayers grown on Si-doped n-type DF GaAs substrates can be converted to semi-insulating by wafer annealing at temperatures higher than 950°C. The resistivity of these semi-insulating epilayers was higher than 10⁷ Ωcm. The outdiffusion of Si from the substrate to the epilayer was analyzed by secondary ion mass spectrometry and it was found that the thickness of the outdiffusion region was only 1μm.     

Compositional inhomogeneity at the epitaxial layer and substrate interface of AlGaAs/GaAs heterostructures

Carrier concentration spikes at the epilayer/substrate interface were observed in some two-dimensional electron gas AIGaAs/GaAs structures grown by low pressure organometallic vapor phase epitaxy. Using secondary ion mass spectroscopy, the carrier spikes were correlated with indium. Under certain growth conditions an anomalous interfacial layer, which is compositionally inhomogeneous, is formed producing an enhanced carrier density. Procedures are described which reduce the presence of indium at the epilayer/substrate interface and eliminate the carrier spike.     

六角相GaN外延膜的高分辨X射线衍射分析研究

通过实例介绍运用高分辨X射线衍射分析技术对GaN异质外延薄膜材料的微结构进行研究，希望能获得不同缓冲层生长与优化工艺以及结构模型对其结构特性参数影响方面的信息，为GaN材料和器件制备者提供有用的参考。     

SiC衬底AlN缓冲层的应变对GaN外延层质量的影响

在3英寸(1英寸=2.54 cm)SiC衬底上采用金属有机物化学气相沉积(MOCVD)法生长GaN外延材料。研究了AlN缓冲层的应变状态对GaN外延层应变状态和质量的影响。使用原子力显微镜和高分辨率X射线双晶衍射仪观察样品表面形貌,表征外延材料质量的变化,使用高分辨喇曼光谱仪观察外延材料应力的变化,提出了基于外延生长的应变变化模型。实验表明,GaN外延层的张应变随着AlN缓冲层应变状态的由压变张逐渐减小,随着GaN张应力的逐渐减小,GaN位错密度也大大减少,表面形貌也逐渐变好。