physica status status solidi (b), 210(2), 869-872 (1998)
C. D. Latham (a), R. Jones (a), J. Wagner (b), B. R. Davidson (c), R. C. Newman (c), C. C. Button (d), P. R. Briddon (e), S. Öberg (f)
(a) School of Physics, University of Exeter, Exeter, EX4 4QL, United Kingdom
(b) Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastrasse 72, D-71908 Freiburg, Federal Republic of Germany
(c) Interdisciplinary Research Centre for Semiconductor Materials, The Blackett Laboratory, Imperial College of Science, Technology and Medicine, London SW7 2BZ, United Kingdom
(d) Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S17 3JD, United Kingdom
(e) Department of Physics, University of Newcastle, Newcastle, NE1 7RU, United Kingdom
(f) Department of Mathematics, University of Luleå, Luleå, SE-97187, Sweden
(Received 8th July 1998)
Heat treatment of heavily carbon doped AlAs and GaAs results in a loss of CAs shallow acceptors. In Raman scattering experiments on annealed CBE grown GaAs with 12C and 13C isotopes, and MOVPE grown AlAs it is found that the loss of carriers is accompanied by the appearance of two high frequency lines. These lie near to the stretch mode of an isolated C2 molecule (1855 cm-1). This is consistent with the formation of two types of di-carbon defects in these materials where the C atoms are bonded together and one or both of which act as a donor.
Using a local density functional method to investigate the structure and dynamics of several di-carbon defects, we find that the dimer at an As site is bistable and aligned approximately in a [100] direction in the neutral charge state, and in a [110] direction when positively ionised. The calculated frequencies lie within 10% of the measured values in both materials. Other defects are investigated too with a view of determining the structures giving rise to the modes.
PACS: 61.72.Vv, 78.30.Fs, S7.12
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