ANHARMONIC INTERACTIONS IN BONDS BETWEEN IMPURITIES AND HOST ATOMS IN GAAS-C AND GAAS-B

摘要

It is demonstrated in GaAs:C and GaAs:B that shifts in frequency of local modes due to impurity isotopes and the associated fine structures arising from isotopes in the host crystal can be reproduced satisfactorily by a model that includes anharmonicity in the stretch force constant between the impurity and its nearest neighbors. The required strength of anharmonicity is of the same order as that implied by a simple Lennard-Jones interaction potential. For the C impurity, the model can also be made compatible with some recent measurements of the energy of the T-2-symmetry second excited state of the local-mode oscillator. Energies of other symmetries of the second excited state and of third excited state are predicted. This work is contrasted with the classic study of CaF2:H- by Elliott et al. [Proc. R. Sec. London, Ser. A 289, 1 (1965)]. In particular, we find that the largest contributions to anharmonic shifts are from processes involving band modes: These processes were not included in the analogous calculations for CaF2:H-. [References: 16]