Defect pairs and clusters related to the EL2 centre in GaAs

Abstract

In this article, we attempt to consistently interpret Deep Level Transient Spectroscopy (DLTS), Electron Paramagnetic Resonance (EPR) and electrical conductivity experimental data for irradiated GaAs. Our analysis reveals the occurrence of an irradiation-induced single donor mid-gap level (MG) related to the AsGa antisite defect. We give evidence that MG can be identified with the deep level associated to the native bulk centre EL2. We make use of a model we have recently developed for the calculation of inter-defect phonon-assisted tunnelling rates. We calculate the nearest neighbour defect-induced hopping conductivities. In heavy dose irradiated GaAs, the DC conductivity is attributed to hopping between MG defects. Our calculations provide extremely good fits to the experimental results of Deng et al. for the DC electrical conductivity in GaAs induced by argon ion bombardment for temperatures ranging from around 20 K to 500 K. The phonon energy ħω (20 ± 2 meV) and Franck-Condon shift Sħω (145 ±10 meV) of MG needed to achieve this fit are in very good agreement with the ħω and Sħω values earlier determined for the native EL2 defect. The bulk AC hopping conductivity has also been calculated and found to agree well with experimental results of Mares et al. for high purity semi-insulating GaAs. The corresponding low-frequency AC conductivity is attributed entirely to a homogeneous random distribution of native mid-gap donor defects EL2. We are also led to invoke the mid-gap level MG (identifiable with that of EL2) in order to account for DLTS results. In fast-electron irradiated n-GaAs, the two high temperature DLTS peaks E4 and E5 are both accounted for by two defect pairs each including an MG level component. In heavy-particle bombarded n-GaAs damage clusters including MG defects account for the experimentally recorded high temperature DLTS peak. For these defect pairs and clusters, our DLTS simulations correctly predict the observed peak positions and their dependence on the electric field.