Electroreflectance and photoluminescence study of InN

Abstract

Photoluminescence and electroreflectance (ER) measurements on InN thin films grown by metal-organic chemical vapour deposition were performed at ambient and low temperatures. Franz-Keldysh oscillations (FKO's) were observed in the ER spectra. From the analysis of the FKO's, the bandgap of an as-deposited film is estimated to be 0.66 ± 0.02 eV at 90 K, whereas the low-temperature (8 K) photoluminescence (PL) appears as a broad peak between 0.67 eV and 0.77 eV. When the sample is annealed in air at temperatures below 420 °C, the bandgap energy at 90 K estimated from the FKO redshifts to 0.62 ± 0.02 eV. When the sample is annealed at temperatures of 420 °C or above, the low energy PL disappears, but the FKO signal persists with the same bandgap energy. We interpret that the crystalline quality of InN improves with annealing at lower temperatures but degrades dramatically with higher temperature annealing and conclude that the intrinsic bandgap energy of InN at 90 K is 0.62 ± 0.02 eV.