Photoreflectance (PR) of surface-intrinsic-n+ type GaAs has been measured for various temperatures, then we can get the energy of E0+£G0 transition in various temperatures. The spectra exhibited many Franz-Keldysh oscillations, when probe beam¡¦s energy is larger than energy gap. Electric field (F) and transition energy can be determined from analyzing the Franz-Keldysh oscillation. Further more we can get the surface¡¦s Fermi level from the dependence of surface¡¦s electric field (Fs) on temperature (T).

The photoreflectance(PR) and Electroreflectance(ER) of surface-intrinsic-n+ type doped GaAs exhibit many Franz-Keldysh oscillations (FKOs), which enable the electric field (F) to be determined from the technique of the fast Fourier transform (FFT). It is known that F's determined from PR are subjected to photovoltaic effect, but it is difficult to estimate the strength of modulating field (dF) of the pump beam in the PR measurements . Alperovich et. al. have used imaginary part of FFT to determine the strengths of dF's in the ER measurements [V. L. Alperovich, et. al. Appl. Phys . Lett. 71, 2788 (1997)]. Here, we will apply this method to the PR measurements. The dF's thus obtained will be compared with those deduced from photo-voltage measurements. The result shows that the method of Alperovich's can be used to determine the strength of dF in the PR measurements.