Resonant Raman scattering as a probe of intrinsic defects in GaAs

This thesis presents a series of Raman-scattering measurements performed on GaAs samples irradiated with either high-energy electrons or neutrons. The irradiation creates fairly high concentrations (1017-1018 cm-3) of intrinsic defects. It is demonstrated that Raman scattering can give useful information about such defects. New and relatively sharp peaks in the Raman spectra of the irradiated samples were observed. These are attributed to vibrational modes of a specific point defect created by the irradiation. On the basis of annealing experiments, it is concluded that one of these models is most likely associated with an As vacancy. The observed polarization dependence suggests that this can be a breathing vibration of the atoms surrounding the vacancy. In addition, experiments were performed that measured the lineshape of the enhancement of the Raman cross section of both the intrinsic and extrinsic modes near the band gap of GaAs using a tunable near infrared laser. It was observed that the enhancement of the defect introduced modes was strong relative to the enhancement of the allowed TO phonon, which itself exhibits a strong enhancement