Transient photocurrent measurements at several temperatures were used to determine the defect level parameters and the density of states distribution in semi-insulating Cr-doped GaAs. A two-dependent-step analysis was applied. Firstly, the energy positions and the attempt-to-escape frequencies of the different defect levels were determined from the Arrhenius plots of the corresponding emission times observed in the transient photocurrent decays. Secondly, the density of states energy distribution g(E) were computed from the same transient photocurrent decays using the Fourier transform technique with an exact matrix solution for g(E). The results obtained for this particular material were: 4 Gaussian bands, peaked around the energies 0.11, 0.21, 0.32 and 0.45eV, with 1017, 1016, 5 x 1015 and 1015/cm3eV as maximum values, respectively. This computed g(E) was introduced as a model of state distribution in an independent numerical simulation to reconstruct the experimental transient photocurrent data, and thus to validate the present analysis for g(E) determination. It was also found that the first transient photocurrent drop for times lower than 100ns was dominated by the initial hole trapping. Full reconstruction required then to take into account the hole current contribution in the transient photocurrent simulation at least at short times.

Determination of Defect Level Parameters in Semi-Insulating GaAs:Cr from Transient Photocurrent Experiment. H.Belgacem, A.Merazga, C.Longeaud: Semiconductor Science and Technology, 2005, 20[1], 56-61