2ND-HARMONIC RESPONSES OF MODULATED PHOTOREFLECTANCE IN SEMICONDUCTORS

The experimental measurements of nonlinear modulated photoreflectance (MPR) phenomena in Si and GaAs wafers, in which the obvious second-har monic (2 f) MPR signals are detected in addition to the fundamental fr equency (f) MPR signals when the pumping laser power is sufficiently s trong, are reported. Meanwhile, a linear-to-quadratic transition in th e curve of the f MPR signal versus the pumping laser power is observed in Si samples but not in GaAs samples. It is also found that the 2 f MPR signals are more sensitive to the ion-implantation doses than the f MPR signals which are traditionally applied to monitor the ion impla ntation in semiconductors. It is found that the contribution of the ph otoinduced modulation of the surface electric field is the main source of the nonlinear MPR signals and the contribution is theoretically di scussed in detail. A one-dimensional theoretical model is established, and the theoretical results are in good agreement with the experiment al data. The dependencies of the f and the 2 f MPR signals on the thir d-order optical nonlinear susceptibility chi(3) and the surface-state density N(S) are also discussed, and a method for measuring chi(3) and N4 of semiconductors is introduced.