Photoluminescence, depth profile, and lattice instability of hexagonal InN films

Abstract

High quality InN films have been grown on (0001) sapphire substrates by metalorganic molecular beam epitaxy, characterized for crystal structure, chemical composition, and optical properties. Depth profiling indicated a high, increasing oxygen concentration profile towards the volume of the film. Photoluminescence revealed two different, coexisting features: a low energy transition around 0.8 eV, and a high energy feature, peaking near 2 eV. The former band originates from the direct transition in the near surface range. The latter, low intensity band results from the bulk region. Oxynitride formation has been accounted for a spatially varying optical band gap EG, determined to 0.61 eV for pure, defect free material. X-ray diffraction analysis supports defect mediated lattice instability, as proposed recently by a molecular dynamic lattice theory.