Observation of Electric Fields at Surface and Interface of Doped GaAs/Semi-insulating GaAs Structures by Fast Fourier Transformed Photoreflectance

Abstract

Room-temperature photoreflectance (PR) measurements were successfully used to investigate electric fields at the surface and interface of doped GaAs/semi-insulating GaAs structures grown by molecular beam expitaxy (MBE). Fast Fourier transform (FFT) was applied to the PR spectra measured using a He–Ne laser as the pump light. The transformed spectra exhibited two well-resolved peaks, while two different Franz-Keldysh oscillation periods could not be distinguished in the original PR spectra. Using an Ar+ laser as the pump light, the FFT PR spectra showed only one peak. Because of the difference in the penetration depth of these two pump beams, the PR spectra taken with the He–Ne laser had contributions from the surface and the interface, while those taken with the Ar+ laser had only contributions from the surface. The measured electric fields at the surface and interface in GaAs with different doping levels were discussed in relation to the calculated electric fields.