Infrared absorption by point defects in gallium arsenide

A calculation of the impurity induced infrared absorption in GaAs is presented on the basis of a Green function technique. Numerical values for the scalar effective charges of different single defects and their lattice neighbours have been obtained by comparison with the experimental absorption rates. It is shown that the full effective charge tensor has to be employed for the description of double defect absorption bands, although the non-diagonal elements are likely to be small compared with the diagonal elements. Good agreement between theory and experiment is found for the proposed structure of a Te-Li complex.