Point defects and their reactions in e--irradiated GaAs investigated by x-ray-diffraction methods.

Abstract

Semi-insulating as well as n-type and p-type GaAs wafers have been irradiated at 4.5 K with 3-MeV electrons up to doses between 0.6 and 3.6\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$/${\mathrm{cm}}^{2}$. Without intermediate warming the irradiated samples were investigated by measurements of the change of the lattice parameter and of the diffuse scattering intensity close to different Bragg reflections. These measurements give direct access to the structure of interstitial atoms in GaAs. Two types of Frenkel defects can be distinguished due to their different annealing at room temperature and around 500 K, respectively. The details of the distribution of the scattering intensity indicate the dominating role of close Frenkel pairs with a typical distance of \ensuremath{\approxeq}10 \AA{} between vacancies and interstitial atoms for the structure of the low-temperature defects. The unusually large strain field or the relaxation volume of \ensuremath{\approxeq}2.0 atomic volumes indicates in addition that these defects arise from double displacements. The Frenkel pairs that anneal around 500 K are characterized by a much smaller relaxation volume of \ensuremath{\approxeq}1 atomic volume. Defect introduction rates of \ensuremath{\approxeq}1 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ have been determined and show that total defect densities of 3\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ can be achieved without indication of saturation or defect clustering. The defect reactions during irradiation as well as during thermal annealing up to 800 K are discussed with special emphasis on the trapping and detrapping of mobile interstitials at other intrinsic defects and the suppression of the formation of dislocation loops. There is no relevant difference observed between the differently doped samples after these high dose irradiations. \textcopyright{} 1996 The American Physical Society.