Optical properties of InN films grown by molecular beam epitaxy at different conditions

InN films were grown by N2 plasma-assisted molecular beam epitaxy on Al2O3 substrates with GaN buffer layers at different substrate temperatures from 200 to 500 °C. It was found that the crystal quality of InN films was improved with growth temperature. The optical absorption edge of InN films decreased from 1.8 to 1.1 eV with increasing substrate temperature from 200 to 500 °C. Photoluminescence measurement on InN films grown at 500 °C exhibited the band-edge emission at around 1.0–1.1 eV.