Effects of the narrow band gap on the properties of InN

Infrared reflection experiments were performed on wurtzite InN films with a range of free-electron concentrations grown by molecular-beam epitaxy. Measurements of the plasma edge frequencies were used to determine electron effective masses. The results show a pronounced increase in the electron effective mass with increasing electron concentration, indicating a nonparabolic conduction band in InN. We have also found a large Burstein-Moss shift of the fundamental band gap. The observed effects are quantitatively described by the $\mathbf{k}\cdot \mathbf{p}$ interaction within the two-band Kane model of narrow-gap semiconductors.