INVESTIGATION OF PHOTOACTIVE SURFACE ELECTRON STATES IN GALLIUM ARSENIDE BY INFRARED SPECTROSCOPY.

A study was made of the surface infrared photoconductivity of pure epitaxial n-type GaAs films at 77 degree K. An analysis of the kinetic, steady-state, lux-ampere, and spectral characteristics of the surface impurity ″frozen″ photoconductivity led to a method for the determination of the distribution of the levels of photoactive centers in the band gap on the surface of a wide-gap semiconductor and for finding the dependence of the photoionization cross section of such centers on the incident photon energy. The results indicate a continuous distribution of surface electron states in the band gap of GaAs, an increase in the photoionization cross section with the photon energy hv in the case of these continuously distributed centers, and reduction in the strength of the electron-phonon coupling in the case of the surface centers relative to the corresponding coupling in the case of the bulk centers.