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 arsenic or gallium ions with subsequent annealing at different temperatures were studied by transmission electron microscopy, Rutherford backscattering spectrometry-channeling, double crystal x-ray diffraction. Optical absorption, electrical conductivity, Hall effect and time-resolved photoluminescence were applied to monitor changes in electrical and optical characteristics of the material. An important conclusion from this investigation is that there was hardly any difference between materials implanted with gallium or arsenic. For implantation of either species, a large number of point defects was introduced and for a high enough dose a buried amorphous layer was formed. Hopping conduction and high absorption below band-to-band transition were observed for both 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 nonstoichiometry of the material at the upper and lower amorphous-crystalline interfaces. Structural studies showed the presence of some residual damage (a band of polycrystalline material in the center of the regrown area) with some associated strain even after annealing at high temperatures. Recovery to the conduction band transport in annealed samples was observed but mobilities, of the order of 2000 cmWs, were still smaller than in unimplanted GaAs. These results show that, in as-implanted material and even after annealing at lower temperatures, the point defects introduced by the implantation are responsible for the very short photocarrier lifetime.