摘要
通过显微拉曼散射对用金属有机化学气相沉积(MOCVD)法在Al2O3 衬底上生长的六方相GaN和掺Mg的p型GaN薄膜进行了研究。在两个样品的拉曼散射谱中同时观察到位于640, 660cm-1附近的两个峰,640cm-1的峰归因于布里渊区边界(L点)最高声学声子的二倍频,而660cm-1的峰为布里渊区边界的光学声子支或缺陷诱导的局域振动模。掺Mg的GaN在该处的峰型变宽是Mg诱导的缺陷引起的加宽或Mg的局域模与上述两峰叠加的结果。在掺Mg的样品中还观察到276, 376cm-1几个局域模并给予了解释。同时掺Mg的GaN中出现了应力弛豫的现象,掺Mg引起的失配位错和电子声子相互作用都有可能对E2 模的频率产生影响。
Raman scattering spectra of GaN and Mg-doped GaN films grown by metal-organic chemical-vapor deposition (MOCVD) on sapphire substrate are investigated. Some weak peaks are also observed in two spectra besides the allowed E 2 and A 1(LO) phonon modes in Z(X-)Z backscattering geometry. The origins of these peaks are discussed and the differences between two spectra are compared. Two peaks at 640 and 660 cm -1 are observed both in the spectra of GaN and Mg-doped GaN samples. The 640 cm -1 peak is attributed to an overtone process of the highest acoustic-phonon branch at the zone boundary (L point). The peak at 660 cm -1 is attributed to the optical-phonon branch at the zone boundary or the local vibrational mode induced by defect. In the spectrum of Mg-doped GaN sample there is a broad feature near the two peaks. It is suggested that the broad feature arises from the local vibrational mode of Mg-N bond which superposed on the two peaks mentioned above or arises from defect-induced broaden. Two additional peaks at 276 cm -1 and 376 cm -1 are also observed in the spectrum of Mg-doped GaN sample. The peak at 276 cm -1 is the local vibrational mode of Mg-N bond and the peak at 376 cm -1 is the local vibrational mode of impurity- defect complex. The frequency of E 2 mode in Mg-doped GaN shifted to low energy side compared with GaN sample, and located at 568 cm -1 at room temperature. This indicated that the relaxation of residual stress existed in Mg-doped sample. The stress relaxation is contributed to Mg-induced generation of dislocation. Furthermore, electron-phonon interaction also can induce frequency shift of E 2 mode.
出处
《发光学报》
EI
CAS
CSCD
北大核心
2005年第2期229-232,共4页
Chinese Journal of Luminescence
基金
国家自然科学基金资助项目(10474078)
关键词
氮化镓
拉曼散射
应力松弛
GaN
Raman scattering
stress relaxation
