Structures and optical properties of H2+-implanted GaN epi-layers

Abstract

The implantation damage build-up and optical properties of GaN epitaxial films under H2+ ion implantation have been investigated by a combination of Rutherford backscattering in channeling geometry, Raman spectroscopy, UV-visible spectroscopy and transmission electron microscopy. GaN epitaxial films were implanted with 134 keV H2+ ions to doses ranging from 3.75 × 1016 to 1.75 × 1017 H2+ cm-2 at room temperature or the same dose of 1.5 × 1017 H2+ cm-2 at room temperature, 573 and 723 K. The dependence of lattice disorder induced by H2+-implantation on the ion dose can be divided into a three-step damage process. A strong influence of the H concentration on the defect accumulation is discussed. The decrease in relative Ga disorder induced by H2+-implantation is linear with increasing implantation temperature. The absorption coefficient of GaN epitaxial films increases with increasing ion dose, leading to the decrease in Raman scattering spectra of Ga-N vibration. With increasing implantation doses up to 5 × 1016 H2+ cm-2, nanoscale hydrogen bubbles are observed in the H deposition peak region. Interstitial-type dislocation loops are observed in the damaged layer located near the damage peak region, and the geometry of the dislocation loops produced by H implantation is analyzed. The surface layer is almost free of lattice disorder induced by H2+-implantation.