Defects in ion implanted and laser irradiated GaAs

Abstract

For special implantation conditions (light ions, sufficiently high implantation temperatures in the case of heavier ion masses) defects are created in GaAs, the back-scattering minimum yield of which does not show a pronounced direct backscattering part.Optical measurements show absorption tails near the fundamental absorption edge with an exponential dependence of the absorption coefficient K on the photon energy [ K -exp ( A W E )]which is connected with almost no refractive index change (AnlnQ0.01). The characteristic energy € varies between 0.2 eV and 0.52 eV depending only on the nuclear deposited energy density but not on the implanted ion species. In elementary semiconductors, e.g. silicon, such a pronounced near-edge absorption is not found. Taking into consideration the results received for laser irradiated GaAs' we conclude that the defects responsible for this behaviour are of the native type. Theoretical considerations have shown that the high values of E as well as the small refractive index change can be explained by assuming high concentrations of vacancies and antisite defects. Further information about. the nature of these defects was found by a careful defect analysis of the backscattering minimum yield for different temperatures as described in Ref. 3. Preliminary experiments show that large concentrations ( -50%) of point defects with small distances from the lattice site are most probable, which is consistent with the conclusion from the optical data.