Behavior of photoconductivity transients due to multiple trapping by a Gaussian distribution of localized states

The decay of excess carriers in semiconductors was analyzed under conditions of multiple trapping by a Gaussian distribution of subband gap states and recombination. Numerical solutions to the rate equations involving multiple trapping in subband gap states and recombination indicate that a power-law decay is observed only under limited conditions. The concept of an optimally filled energy level for which a ratio of the trapping time to the release time has a minimum is introduced for the Gaussian distribution. We showed that the position of the Fermi level may limit the portion of the distribution that can be effective in the decay. The results provide an explanation for the nonlinear temperature dependence of the exponential term ${\alpha }_1$ that is sometimes observed experimentally.