Influence of strain on the band gap energy of wurtzite InN

Degenerate wurtzite InN films with electron concentrations in the range of 10(18) cm(3) were studied by using spectroscopic ellipsometry (SF) in two spectral ranges . The analysis of the frequencies of the coupled phono-plasmon modes in the mid-infrared region allows the determination of the plasma frequency and thus of the carrier density in the bulk of the samples SE from the near-infrared to the invisible range provides the dielectric function (DF) around the absorption edge. The electron concentraion as an important input parameter enables accurate determination of Burstein-Moss shift and band-gap renormalization for the analysis of the imaginary part of the DF. Taking into account the in-plane strain of the films, which is caused by lattice mismatch between InN and buffer/substrate we obtain a zero density strain-free band gap of 0.675 eV at room temperature.