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 operation of various devices based on semi-insulators. We investigate by numerical simulation its role in the transient photoresponse of a planar metal\ufffdsemiconductor\ufffdmetal photodetector. We simulate a realistic case where the active layer is InGaAs made semi-insulating by addition of Fe. The simulation uses a two-dimensional, drift/diffusion calculation with realistic conditions where the semi-insulating material is represented by a two-level compensation model with Fe as a deep acceptor that compensates shallow n-type impurities. The results give a microscopic picture on a picosecond time scale of factors that affect the transient response: trapping, space charge, propagation of the bias field, and the spatial distribution of the carriers.NRC publication: Ye