Charge Redistribution and Potential Barrier Reconstruction in SI GaAs Caused by EL2 State ChangeR. Kiliulis, V. Kazukauskas, J. Storasta and J.-V. Vaitkus
Semiconductor Physics Department of Vilnius University, Sauletekio al.9, bldg.3, 2054 Vilnius, Lithuania
Received 7 September 1995, revised 15 January 1996, accepted 21 May 1996
We report the effects associated with the transition of the EL2 defect to its metastable state EL2* and vice versa in semiinsulating (SI) GaAs. We investigated changes in deep level spectra, the time evolution of the quenching process, and the thermal recovery of the normal state. It was shown that the p-type state introduced by the transformation of EL2 and the associated charge transfer between different defects exists in the dark even above 150 K. Therefore a number of electron and hole traps can be observed separately by the thermally stimulated measurements. A thermal quenching effect of thermally stimulated currents and thermally stimulated Hall mobility has been identified and numerically simulated. A model is proposed to explain charge transfer induced by the photoquenching of EL2, which is based on the change of the compensation ratio of some deep levels, not associated with EL2. Therefore it is not necessary to introduce the "EL2 family" concept. Furthermore, we demonstrate that the exhaustive analysis of the effects associated with the EL2 transformation should include both charge redistribution between numerous levels in the band gap and reconstruction of the potential barrier network as well. The evidence of a primary lattice relaxation associated with an intermediate excited EL2 state is demonstrated. Persistent carrier effects are different in both EL2 states. This confirms that potential fluctuations are modified during the thermal quenching of the EL2 level. A cellular percolation model is presented.
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