AlGaN薄膜的微区Raman散射光谱研究

MICRO RAMAN SPECTRA OF AlGaN FILMS

利用微区Ｒａｍａｎ散射技术，对低压ＭＯＣＶＤ生长的不同Ａｌ组分的ＡｌｘＧａ１－ｘＮ薄膜（ｘ＝０，０．０７，０．１５）进行了背散射Ｚ（Ｘ，Ｘ）Ｚ－几何配制下的测量．Ａ１（ＬＯ）模式的声子频移随Ａｌ组分的变化关系为：ω（ＡｌｘＧａ１－ｘＮ）＝（１＋０．２２０ｘ）ω（ＧａＮ）．观察到了Ａ１（ＬＯ）模式由于空间相关效应引起的展宽．Ｅ２模式随Ａｌ组分的的增大产生的移动很微小，但趋于展宽．这被认为是Ｅ２模式的声子频移随Ａｌ组分的增加而增大与其受到的张应力导致的声子频移随Ａｌ组分的增加而减小共同作用的结果．在多种配置下，观察到了Ａｌ０．０７Ｇａ０．９３Ｎ薄膜的Ａ１（ＴＯ）模式、Ａ１（ＬＯ）模式、Ｅ１（ＴＯ）模式和Ｅ２模式．验证了ＡｌｘＧａ１－ｘＮ薄膜的Ｒａｍａｎ选择定则．表明ＡｌｘＧａ１－ｘＮ薄膜具有单模行为．

Al x Ga 1-x N films with x= 0, 0.07, 0.15 grown by LP MOCVD were measured by micro Raman technique under Z(X,X)Z- configuration. Dependence of Raman shift of A1(LO) mode on Al molar fraction was given by ω (Al x Ga 1-x N) =(1+0.220 x ) ω (GaN) . Broadening of A1(LO) were demonstrated from spatial correlation effect. E2 modes had little shift except small broadening. It was suggested shift increasing of E2 mode with Al molar fraction increasing and shift decreasing due to strain from underlying GaN co effect it. Under various configurations, A1(TO), A1(LO), E1(TO) and E2 modes were observed, and they followed Raman select rules. Single mode behavior of phonon was supported.