Observation of visible luminescence from indium nitride at room temperature

InN films were grown on sapphire substrates with AlN buffer layers by reactive sputtering. C-axis-oriented crystalline InN films with a wurtzite structure were confirmed by x-ray diffraction and Raman scattering. Strong photoluminescence (PL) at 1.87 eV, together with a clear absorption edge at 1.97 eV, was observed at room temperature, which clearly demonstrates that it is not accurate in the previous assignment of an ∼0.7eV fundamental band gap for intrinsic InN simply from PL and absorption data. The possible origin of the present large band gap was discussed in terms of the effects of oxygen and the Burstein-Moss shift.