MODELING THE BEHAVIOR OF PHOTOGENERATED CHARGE IN SEMIINSULATING GAAS

The transient response of photogenerated carriers in semi-insulating ( SI) GaAs is expected to be influenced by the inevitable deep traps in the material. To investigate this effect, and its dependence on the tr ap-compensation scheme, we have simulated the dynamical behavior of ca rriers in a planar structure consisting of Schottky electrodes applied directly to SI-GaAs that is either doped (with Cr) or undoped (with E L2 compensation). We show by a two-dimensional, finite-difference calc ulation how the deep traps lead to photoinduced space charge at the el ectrodes. This space charge screens the bias field and modifies the tr ansient response of the carriers, but the details vary with the type o f trap compensation used in the SI-GaAs. Although we consider for illu stration the simplest possible planar structure, our results relate di rectly to a class of metal-semiconductor-metal photodetectors that is potentially important in integrated optoelectronics.