STRUCTURAL, ELECTRICAL, AND OPTICAL STUDIES OF GAAS IMPLANTED WITH MEV AS OR GA IONS

The structural properties of GaAs implanted with high doses of 2 MeV a rsenic or gallium ions with subsequent annealing at different temperat ures were studied by transmission electron microscopy, Rutherford back scattering spectrometry-channeling, double crystal x-ray diffraction. Optical absorption, electrical conductivity, Hall effect and time-reso lved photoluminescence were applied to monitor changes in electrical a nd optical characteristics of the material. An important conclusion fr om this investigation is that there was hardly any difference between materials implanted with gallium or arsenic. For implantation of eithe r species, a large number of point defects was introduced and for a hi gh enough dose a buried amorphous layer was formed. Hopping conduction and high absorption below band-to-band transition were observed for b oth cases. After low temperature annealing of the amorphous material, a high density of stacking faults and microtwins were found. Regrowth rates at the front and back amorphous-crystalline interfaces showed a significant difference. This was attributed to differences in local no nstoichiometry of the material at the upper and lower amorphous-crysta lline interfaces. Structural studies showed the presence of some resid ual damage (a band of polycrystalline material in the center of the re grown area) with some associated strain even after annealing at high t emperatures. Recovery to the conduction band transport in annealed sam ples was observed but mobilities, of the order of 2000 cm(2)/Vs, were still smaller than in unimplanted GaAs. These results show that, in as -implanted material and even after annealing at lower temperatures, th e point defects introduced by the implantation are responsible for the very short photocarrier lifetime.