Effect of potential fluctuations on the transport properties and the photoconductivity of compensated semiconductors. Application to semi-insulating GaAs. II. Excess carrier lifetimes and photoconductivity

In the presence of potential fluctuations, the continuity equations must be averaged over the sample in order to obtain equations involving physically observable transport quantities. The lifetime of the total carrier population, which can be obtained by initial photoconductivity decay time measurements, differs from the photoconductivity lifetime. The lifetime expressions are derived in the cases of band-to-band and Shockley–Read recombinations. Numerical calculations of the excess carrier densities versus flux and temperature are performed for semi-insulating (SI) GaAs, considering one deep level as a recombination center. The analysis is extended to describe various situations taking into account (i) the presence of a trap, and (ii) both the EL2 and Cr recombination centers. Experimental data are discussed.