Electrical and Optical Enhancement of Photoconductivity in Semi-Insulating GaAs

Abstract

We have observed that the intrinsic photoconductivity of semi-insulating GaAs is enhanced after an excitation of the material by (i) light of photon energy 0.9 eV or (ii) an applied ac electric field of 5×${10}^3$ V/cm. This enhancement differs from those previously observed in that (i) the enhancement is observed after the removal of the excitation causing it and (ii) at 77°K, it persists for a long time (>1 h) even in the presence of the intrinsic light. For the case of electric field enhancement, the peak value of the enhanced photoconductivity may be as much as 10 times larger than the steady-state photoconductivity. This paper describes the characteristics of this enhancement phenomenon and presents a model to explain them. It is concluded that the enhancements caused by the two different excitations described above are related, and that the enhancements in both cases are caused by a charge transfer from a deep impurity level to another through the conduction band. Numerical values of the parameters of the theoretical model are presented for our samples.