Optical bandgap energy of wurtzite InN

Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy. Growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction. We observed at room temperature strong photoluminescence (PL) at 0.76 eV as well as a clear absorption edge at 0.7-1.0 eV. In contrast, no PL was observed, even by high power excitation, at ∼1.9 eV, which had been reported as the band gap in absorption experiments on polycrystalline films. Careful inspection strongly suggests that a wurtzite InN single crystal has a true bandgap of 0.7-1.0 eV, and the discrepancy could be attributed to the difference in crystallinity.