BIAS VOLTAGE PROPAGATION IN A SEMI-INSULATOR - EFFECT ON THE IMPULSE-RESPONSE OF AN INGAAS-FE PLANAR PHOTODETECTOR

A semiconductor with a high resistivity due to a deep trap is called a semi-insulator. A semi-insulator does not always behave like a normal insulator because of so-called bias voltage propagation, which arises from space charge in the deep trap. This effect is a factor in the op eration of various devices based on semi-insulators. We investigate by numerical simulation its role in the transient photoresponse of a pla nar metal-semiconductor-metal photodetector. We simulate a realistic c ase where the active layer is InGaAs made semi-insulating by addition of Fe. The simulation uses a two-dimensional, drift/diffusion calculat ion with realistic conditions where the semi-insulating material is re presented by a two-level compensation model with Fe as a deep acceptor that compensates shallow n-type impurities. The results give a micros copic picture on a picosecond time scale of factors that affect the tr ansient response: trapping, space charge, propagation of the bias fiel d, and the spatial distribution of the carriers.