Instabilities and small-signal response of double injection structures with deep traps

Abstract

The small-signal response is discussed for double injection structures heavily doped with deep recombination centers. The discussion is based on an exact small-signal linearization of the nonlinear equations describing the steady state. Diffusion is neglected, but space charge, thermal emission, and position- and injection-level-dependent lifetimes are included. The problem is reduced to finding the solution of a single second order linear differential equation, which is valid at any injection level. Approximate general solutions are derived for high and low frequencies. Numerical solutions are given for Au-doped silicon p-i-n devices operating in the low injection square-law regime. Previously a much simpler model was used to calculate the small-signal response in this regime, and that model was successful in explaining the spontaneous oscillations observed there. It is demonstrated that the numerical solutions to the exact equation give results very similar to the previous model. A physical description of the space-charge recombination oscillations is given. This description suggests that the space charge on the traps and its phase shift with respect to the free carriers are the important factors giving rise to the oscillatory instabilities.