Frenkel pairs in low-temperature electron-irradiated InP: X-ray diffraction

Semi-insulating InP (Fe) wafers have been irradiated at 4.5 K with 2.5-MeV electrons up to a highest dose of 4\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 of x rays close to different Bragg reflections. These measurements give direct information on the structure of irradiation-induced Frenkel pairs in InP. Most characteristically, the displacement fields around interstitial atoms and vacancies must be of the same size but of the opposite sign. The separation distance of the closest Frenkel pairs is of the order of 6 \AA{}. The introduction rate for the Frenkel pairs of \ensuremath{\Sigma}\ensuremath{\ge}1.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ is nearly constant up to the highest dose. Hence defect densities of n\ensuremath{\ge}5\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ can be accumulated at low temperatures without indication of agglomeration or saturation. The close Frenkel pairs represent about 66% of the initial defects and anneal between 120 K and room temperature. The remaining Frenkel defects have larger distances and anneal within several annealing stages up to a highest temperature of 670 K.