Mechanism for dicarbon defect formation in AlAs and GaAs

Latham, CD; Jones, R; Haugk, M; Frauenheim, T; Briddon, PR

doi:10.1016/S0921-4526(99)00649-3

Mechanism for dicarbon defect formation in AlAs and GaAs

Lookup NU author(s): Professor Patrick Briddon

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Abstract

There is a need to understand the degradation mechanism which results in the loss of substitutional C-As shallow accepters in AlAs and GaAs containing high concentrations (greater than or similar to 10(20) cm(-1)) of carbon. The activation energy for the migration of interstitial carbon atoms, C-i, in AlAs and GaAs is calculated using a local-density functional-based method, AIMPRO, to be less than or similar to 1 eV. This model is consistent with a 'kick-out' mechanism being responsible for the observed loss of C-As, and formation of dicarbon defects. Three local minima separated by only a few tenths of an eV are encountered by a diffusing carbon atom along its path through the crystal. These have (C-As)(As) split interstitial, bond-centred M-C-As, and (C-M)(M) split interstitial structures (M = Al, Ga). Interstitial dicarbon defects, (C-C)(i), or substitutional dicarbon defects, (C-C)(As), are produced depending on whether a C-i meets a (C-M)(M) split interstitial or a C-As These possess Raman-active C-C vibrational modes near to that for a free dicarbon molecule, C-2. (C) 1999 Elsevier Science B.V. All rights reserved.