Band structure parameters of the nitrides: The origin of the small band gap of InN

Abstract

Using the full‐potential linear augmented plane waves (FLAPW) method and adding Christensen’s gaussian potential to the standard Kohn‐Sham equations that allows to correct the band gap in the local density approximation (LDA), we study the chemical trends of the band gap variation in III–V semiconductors and predict that the band gap for InN is 0.8 (±0.1 eV), which is much smaller than previous experimental value of 1.9 eV. The unusually small band gap of InN, that is even smaller than the band gap of InP, is explained in terms of the high electronegativity of nitrogen and consequently the small band gap deformation potential of InN. To understand the possible origin of the measured large band gap, we have calculated the absorption coefficients and effective masses of wurtzite InN and compared the results to the one of GaN. We show that, due to the non‐parabolicity of the bands, using the standard linear interpolation scheme as in the experiments, the derived apparent band gap depends on the choice of the scale used in the measurements. The difference between the apparent band gap and the true band gap could be as large as 0.4 eV for InN, overestimating the true band gap. From the calculated effective masses we have calculated the Moss‐Burstein shift of the band gap as a function of the carrier density. We find that due to the Moss‐Burstein shift, the apparent band gap of InN can reach to 2.0 eV if the electron density in the conduction band is in the order of 1020. Our observations are consistent with recent experiments, where a low band gap of 0.8 eV in InN is reported. This establishes the low value for the band gap in InN.