激光诱导多孔硅晶格畸变的Raman光谱和光致发光谱研究

LASER-INDUCED LATTICE DEFORMATION OF POROUS SILICON REVEALED BY RAMAN AND PHOTOLUMINESCENCE SPECTROSCOPIES

研究了掺钛水热法制备多孔硅的Raman光谱和光致发光谱 .实验发现 ,当激光功率较低时 ,多孔硅的Raman光谱在略低于 5 2 0cm- 1 附近表现为一锐的单峰 ,和晶体硅的Raman光谱类似 .随激光功率增大 ,该单峰向低波数移动 ,Raman和光致发光峰的强度与激光强度的一次方成正比 .当激光功率增大到一定值时 ,该单峰分裂成两个Raman峰 ,光致发光谱的强度突然增大 ,与激光强度之间不再满足一次方的关系 ,位于低波数一侧的Raman峰随激光功率增大进一步向低波数移动 .多孔硅Raman光谱随激光功率的变化是由于激光诱导多孔硅的晶格畸变 ,导致LO和TO模的简并解除引起的 .同时 ,激光诱导晶格畸变可能使多孔硅由线性变为非线性光学材料 ,而且具有非常大的光致非线性吸收系数 .更重要的是 ,多孔硅的Raman光谱和光致发光谱随激光功率变化的现象是可逆的 ,这可能预示着多孔硅一些新的应用 .

Raman and photoluminescence spectroscopies fo the porous silicon prepared in a hydrothermal solution with addition of titanium have been studied. Only a sharp single band near 520cm(-1) appears in the Raman spectrum of the porous silicon when the exciting laser power is low and shifts to the red side with the increase of the laser power. If the laser power is increased to a critical value, the Raman band splits into two bands while the photoluminescence band splits also and the intensity of it increases enormously. We assign the two Raman bands to the lattice deformation-induced non-degeneracy of the LO and TO phonons. The laser-induced lattice deformation may result in the transformation of the porous silicon from a linear to a nonlinear optical material with a large laser-induced nonlinear optical absorption coefficient. It is found that the laser-induced transformation in the porous silicon is a reversible process. This may implicate some new applications of this material.