New evidence of small lattice relaxation for the D X center in AlxGa1−xAs

Local structure of isolated Si impurity in GaAs and AlAs is studied using a parameter-free semi-empirical tight binding method. It is predicted that nearest neighbor As atom around the impurity moves toward SiGa(Al) causing a 6.54% (5.73%) change in GaAs(AlAs) bond length. An estimation of lattice distortion energy 0.02±0.003 eV (0.025±0.003 eV) for GaAs:Si (AlAs:Si) is found in good qualitative agreement with the value obtained by J. C. M. Henning and J. P. M. Ansems [Semicond. Sci. Technol. 2, 1 (1987)] from the photoionization of the DX center in lightly doped Si impurities in Al0.33Ga0.67As. The fits for the observed maxima in the optical cross section and the calculation of the pressure-dependent thermal barrier energy lend support for the small lattice relaxation models and cast doubt on the validity of those with the large lattice relaxation usually recommended for this class of centers.