Bandgap energy of InN and its temperature dependence

InN crystals are grown on sapphire substrates by a plasma assisted MBE system. The carrier concentration of the samples are 2 × 1018−1 × 1019 cm–3. Optical transmission and reflectance measurements are performed on these samples in a temperature range of 8–300 K. The resultant spectra are analysed by theoretical spectra based on a LO-phonon plasmon coupling scheme for phonon related factor and non-parabolic conduction band structure for electronic transition factor. The observed absorption edge is estimated to mainly originate from the valence band to conduction band transition rather than defect or impurity related transition on the basis of the electron concentration dependence of the momentum matrix element. The bandgap energy is about 0.63 eV, and increases with the temperature decrease. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)