Experimental consideration of optical band-gap energy of wurtzite InN

Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy (MOVPE). Growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering with polarized geometry, X-ray diffraction, and reflection high-energy-electron diffraction. In the growth, an extremely high V/III ratio of around 700000 was used to suppress inclusion of metal-indium. We observed at room temperature strong photoluminescence (PL) at 0.75 eV as well as a clear absorption edge at 0.7-1.0 eV. In contrast, no PL was observed, even at high power excitation of 0.6MW/cm² at ∼1.9 eV, which had been reported as the band-gap in absorption experiments on single crystalline films grown by microwave-excited MOVPE and poly-crystalline ones. Careful inspection strongly suggests that a wurtzite InN single crystal has a true band-gap energy of 0.7-1.0 eV, and the discrepancy between this and previous data could be due to the difference in the crystallinity of the materials measured.