n-SiC拉曼散射光谱的温度特性

Temperature-dependent Raman property of n-type SiC

测量了采用离子注入法得到掺N的n-SiC晶体从100—450K的拉曼光谱.研究了SiC一级拉曼谱、电子拉曼散射谱及二级拉曼谱的温度效应.实验结果表明,大部分SiC一级拉曼峰会随温度升高向低波数方向移动,但声学模红移(峰值位置向低频方向移动)的幅度较光学模小.重掺杂4H-SiC的纵光学声子等离子体激元耦合(LOPC)模频率随温度升高表现出先蓝移(峰值位置向高频方向移动)后红移的变化趋势,表明LOPC模的温度特性不仅会受到非简谐效应的影响,还与实际已离化杂质浓度有关.电子拉曼散射峰线宽随温度升高而增大,强度随温度升高而减弱,但其峰值位置基本不变.二级拉曼谱的红移不如一级拉曼谱明显,但其峰值强度却随着温度的升高显示出明显下降的趋势.

Micro-Raman scattering from the nitrogen doped n-SiC is performed at the temperatures ranging from 100 to 450 K. The temperature dependences of the first-order Raman scattering,electronic Raman spectra and the second-order Raman features are obtained. These measurements reveal that most of the first-order Raman phonon frequencies decrease with temperature increasing,but the redshifts of the acoustic phonon modes are smaller than those of the optical phonon modes. Meanwhile,the longitudinal optical phonon-plasma coupled （LOPC） mode manifests different features with temperature increasing. The LOPC mode tends to have a blueshift at a lower temperature but a redshift at a higher temperature. This indicates that the temperature dependence of LOPC mode is affected not only by the anharmonic effects,but also by the ionized donor concentration. With the increase of the measurement temperature,the intensity of the electronic Raman spectrum decreases,and the linewidth gradually broadens,but the electronic Raman signal is almost not shifted. The redshift of the second-order Raman spectrum is smaller than that of the first-order Raman spectrum,but the intensity of the second-order Raman spectrum substantially decreases with the increase of temperature.