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

Abstract

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 × 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.

Density of states in Bi12TiO20from time-of-flight measurements

“…It means that the carrier distribution in the sample has no influence on the external current and that the whole system behaves exactly as in the case of a transient photocurrent (TPC) experiment [25,26]. This latter experiment is performed with a sample in coplanar geometry.…”

Determination of semiconductor band gap state parameters from photoconductivity measurements. II. Experimental results

“…It is worth noting that this GaAs:Cr sample has already been studied by the modulated photocurrent, high-resolution photoinduced transient spectroscopy ͑HRPITS͒, and transient photocurrent ͑TPC͒ techniques. 9,10 In one of these publications 9 we have given different methods to derive the energy position and capture coefficient of a given defect state from the analysis of the MPC-HF data. The agreement between all these techniques was rather satisfying and some peak energy positions as well as the corresponding electron capture coefficients were determined for this crystal.…”

“…In particular, a peak located at 0.43-0.45 eV below the conduction band edge, with a value of C n N c of 3-8ϫ 10 11 s −1 , was put into evidence. 10 We present in Fig. 1 the NC / distribution obtained from the MPC-HF technique ͑lines͒.…”

Characterization of semi-insulating GaAs:Cr by means of DC-CPM technique

“…The DOS was obtained by differentiation of the absorption curve method described by Pierz et al [15]. (i) the lower part close to conduction band edge is derived from transient photocurrent measurement TPC, [2], high resolution photo induced transient spectroscopy HRPITS and modulated photocurrent measurements MPC [3],…”

“…GaAs can be doped with Chromium (Cr) in order to obtain a semi-insulating gallium arsenide (SI-GaAs:Cr) substrate as silicon dioxide. Chromium behaves as an acceptor with an impurity level close to the centre of the energy gap [1][2][3].…”