Determination of defect level parameters in semi-insulating GaAs : Cr from transient photocurrent experiment

摘要

Transient photocurrent (TPC) measurements at several temperatures are used to determine the defect level parameters and the density of states distribution in semi-insulating Cr-doped GaAs. A two-dependent-step analysis is applied. Firstly, we determine the energy positions and the attempt-to-escape frequencies of the different defect levels from the Arrhenius plots of the corresponding emission times observed in the TPC decays. Secondly, we compute the density of states energy distribution g(E) from the same TPC decays using the Fourier transform technique with an exact matrix solution for g(E). The results obtained for this particular material are: four Gaussian bands, peaked around the energies 0.11, 0.21, 0.32 and 0.45 eV, with 10(17), 10(16), 5 x 10(15) and 10(15) cm(-3) eV(-1) as maximum values, respectively. This computed g (E) is introduced as a model of state distribution in an independent numerical simulation to reconstruct the experimental TPC data, and thus to validate the present analysis for g (E) determination. It is also found that the first TPC drop for times lower than 100 ns is dominated by the initial hole trapping. Full reconstruction requires then to take into account the hole current contribution in the TPC simulation at least at short times.