Physica B, 273-274, 784-787 (1999)

Mechanism for dicarbon defect formation in AlAs and GaAs

C. D. Latham (a), R. Jones (a), M. Haugk (b), Th. Frauenheim (c), P. R. Briddon (d)

(a) School of Physics, University of Exeter, Exeter, EX4 4QL, UK

(b) Institut für Physik, Theoretische Physik III, Technische Universität, D-09107 Chemnitz, Germany

(c) Theoretische Physik, Fachbereich Physik, Universität-GH Paderborn, D-33098 Paderborn, Germany

(d) Department of Physics, University of Newcastle, Newcastle, NE1 7RU, UK

Abstract

There is a need to understand the degradation mechanism which results in the loss of substitutional C_As shallow acceptors in AlAs and GaAs containing high concentrations (> 10²⁰ 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 < 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-As)_As, are produced depending on whether a C_i meets a (C-M)_M split interstitial or a C_As.  These posses Raman-active C-C vibrational modes near to that for a free dicarbon molecule, C₂.

PACS: 66.30.Jt, 61.72.Bb, 61.72.Ji, 71.15.Nc

Keywords: Aluminium-arsenide, Gallium-arsenide, Defects, Carbon, Diffusion

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