Frenkel pairs in low-temperature electron-irradiated InP: Optical-absorption spectroscopy.

Abstract

Semi-insulating InP (Fe) wafers were irradiated at 4.5 K with 2.2-MeV electrons. The irradiation dose was varied between 2\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$/${\mathrm{cm}}^{2}$ and 3\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$/${\mathrm{cm}}^{2}$ and the samples were transferred in liquid nitrogen to an optical cryostat for the investigation of the magnetic circular dichroism of the optical absorption (MCDA) and the infrared absorption. After irradiation we observed two new MCDA spectra that increase linearly with dose and are attributed to close Frenkel pairs. These spectra anneal around 200 K (stage I) and seem to represent the spectroscopic evidence for intrinsic defects that anneal below room temperature. Along with the annealing of these close Frenkel pairs, two well-known MCDA spectra appear that had been related to the ${\mathrm{P}}_{\mathrm{In}}$ antisite and to impurity-defect complexes, respectively. The impurity-defect complexes anneal between 330 and 400 K (stage II) whereas the final annealing of the ${\mathrm{P}}_{\mathrm{In}}$ antisites is observed around 650 K. Along with this final annealing the MCDA band of the Fe acceptor is completely recovered. A well-known infrared absorption band (${\mathit{E}}_{\mathrm{photon}}$\ensuremath{\ge}0.77 eV) is shown to be directly formed during irradiation. The underlying defect reactions are discussed with special emphasis on the correlation to previously published diffuse x-ray-scattering results.