Defect structure and recovery in hydrogen-implanted semi-insulating GaAs

A beam of low-energy positrons together with ion-beam techniques have been used to profile defect and hydrogen distributions and their annealing behavior after the room-temperature implantation of 3\ifmmode\times\else\texttimes\fi{}${10}^{15}$ to 1\ifmmode\times\else\texttimes\fi{}${10}^{17}$ 60-keV ${\mathrm{H}}^{+}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ in semi-insulating GaAs. A monovacancy overlayer is observed close to the surface at 0\char21{}330 nm after 1\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{H}}^{+}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ implantation. The vacancies in the stopping range of the implanted H at 330\char21{}720 nm are seen only after the annealing at 200 \ifmmode^\circ\else\textdegree\fi{}C, probably due to a release of hydrogen from the vacancies. The total vacancy depth of 720 nm correlates well with the distribution of displaced atoms and with the energy deposited in the H implantation. Above 350 \ifmmode^\circ\else\textdegree\fi{}C, the monovacancies in the region of 0\char21{}350 nm start to disappear, whereas at the depth of 350\char21{}750 nm stable vacancy-hydrogen agglomerates are formed at 400 \ifmmode^\circ\else\textdegree\fi{}C. The redistribution of the implanted hydrogen at 0\char21{}350 nm was observed to be connected with the migration of complexes containing implantation-induced defects.