Effect of Traps on Carrier Injection in Semiconductors

The effect of carrier traps on the behavior of a semiconductor with respect to injected carriers is analyzed. Two problems are considered: photoconductivity, and spread of excess carrier concentration under applied field. It is shown that trapped minority carriers, by causing an increase in majority carrier concentration, give rise to increased photoconductivity which may be nonlinear with light intensity and have a very long time constant. These conclusions are in agreement with recent experimental results. The drift of excess carriers is treated, neglecting diffusion. Expression is obtained for the time and space distribution of excess minority carriers, and the effect of traps on the apparent drift mobility is discussed.