Infrared-absorption properties ofEL2 in GaAs

The optical properties of semi-insulating bulk GaAs, grown with the liquid-encapsulated Czochralski techniques, were studied in the spectral region of 5000–11 150 ${\mathrm{cm}}^{\mathrm{-}1}$ using a high-resolution Fourier-transform infrared spectrophotometer. The zero-phonon line associated with the intracenter transitions, observed at 1.039 eV and at temperatures less than 12 K, was found to exhibit a complex structure. This structure indicates that the EL2 center is composed of different but similar energy levels, each with one zero-phonon line. The intracenter transitions responsible for the absorption band between 1.03 and 1.27 eV show a structure involving phonon replicas at an average energy interval of 11.5±0.8 meV, which is larger than that of transverse-acoustic phonons suggesting that other couplings may exist.