VACANCY DEFECTS IN PHOTOEXCITED GAAS STUDIED BY POSITRON 2-DIMENSIONAL ANGULAR-CORRELATION OF ANNIHILATION RADIATION

The positron two-dimensional angular correlation of annihilation radia tion (2D-ACAR) technique has been coupled with optical excitation to s tudy the native point defects in semi-insulating GaAs. The As vacancy was observed below similar to 170 K when illuminated with 1.41+/-0.07 eV photons. The temperature dependence of the 2D-ACAR spectra, with an d without illumination, was studied. Data were also collected at 25 K as a function of the intensity of infrared light. The 2D-ACAR spectra reflect the e(+)-e(-) pair momentum distribution at or near the vacanc y and provides symmetry and electronic structure information, which ca n be used as a unique defect signature for the vacancy.