GaN layers with different polarities prepared by radio frequency molecular beam epitaxy and characterized by Raman scattering

GaN layers with different polarities have been prepared by radio-frequency molecular beam epitaxy （RF-MBE） and characterized by Raman scattering. Polarity control are realized by controlling A1/N flux ratio during high temperature A1N buffer growth. The Raman results illustrate that the N-polarity GaN films have frequency shifts at A1 （LO） mode because of their high carrier density; the forbidden A1 （TO） mode occurs for mixed-polarity GaN films due to the destroyed translation symmetry by inversion domain boundaries （IDBS）; Raman spectra for Ga-polarity GaN films show that they have neither frequency shifts mode nor forbidden mode. These results indicate that Ga-polarity GaN films have a better quality, and they are in good agreement with the results obtained from the room temperature Hall mobility. The best values of Ga-polarity GaN films are 1042 cm^2/Vs with a carrier density of 1.0× 1017 cm^-3.

掺铕GaN薄膜的Raman散射研究

采用金属有机物化学气相沉积(MOCVD)和离子注入的方法制备了掺铕GaN薄膜。利用Raman散射技术研究薄膜的晶格振动,从而确定离子注入引进的晶格损伤变化情况。结果表明,Eu离子注入剂量越大,对晶格的损伤越严重;Eu离子注入的能量越高,对晶格的损伤也越严重;采用沟道注入方法可以有效地减小对晶体的损伤。离子注入后进行高温退火,可以使晶格中的Ga空位引起的缺陷得到有效的恢复,而N空位引起的缺陷随着退火温度的升高先减少后增多。不同几何配置的Raman谱研究表明,1000℃的高温退火导致了GaN的分解。

采用偏振喇曼光谱研究AlN晶体(110)面的各向异性

采用平行及垂直配置下的偏振散射装置,对物理气相传输(PVT)法同质籽晶生长的六方AlN晶体进行偏振喇曼研究,测量了激发光偏振方向与光轴成不同角度时各个振动模的偏振喇曼光谱,得到不同振动模式的喇曼信号强度变化。结果表明,对于A1(TO)和E1(TO)振动模,在平行及垂直偏振配置下,其喇曼强度曲线的变化周期均为π/2,相位差均为π/4;对于E■振动模,在平行和垂直偏振配置下,其喇曼强度曲线的变化周期分别为π及π/2。通过喇曼选择定则及实验数据拟合分析得到AlN晶体各个振动模的喇曼张量比,其中,A1(TO)、E1(TO)和E■振动模的喇曼张量比为ZnO的2~3倍。垂直偏振配置下,AlN晶体的喇曼张量比远大于4H-SiC材料,为4~7倍,表明AlN晶体具有更强的各向异性,为纤锌矿结构材料的各向异性研究提供依据。