TRANSIENT DOUBLE INJECTION IN TRAP-FREE SEMICONDUCTORS

When a step voltage is applied to injecting contacts on the ends of a long trap-free semiconductor, such as p-type germanium, an electron-hole plasma forms at the minority-carrier injecting end and propagates down the length of the bar. When the recombination time (τ) is much longer than the small-pulse transit time (t0), the leading edge of the propagating plasma arrives at the far end at ta=(5/6)t0. The arrival is marked by a cusp in the time derivative of the current, which can be used to measure the minority-carrier mobility. After ta, the current acquires an exponential form, with a time constant equal to the recombination time. Approximate analytic solutions and numerical results indicate that the important recombination effects are small (<2%) for τ/t0 greater than about 2. Early-transient diffusion effects are small when (applied voltage/thermal voltage)1/2 is greater than about 40. All the prominent features can be described in terms of simple physical concepts, and the theoretical predictions are verified by experiment. © 1969 The American Institute of Physics.