We present a comprehensive study of the $\mathrm{InN}$ dielectric function from the midinfrared range up to $6.5\mathrm{eV}$ employing spectroscopic ellipsometry at room temperature. The single-crystalline $\mathrm{InN}$ films with Hall concentrations varying between $7.7\times {10}^{17}$ and $1.4\times {10}^{19}{\mathrm{cm}}^{-3}$ were grown by molecular-beam epitaxy on sapphire substrates and show high structural quality. Free-carrier and phonon properties are determined precisely. The onset of the absorption edge reveals a distinct blueshift with increasing free-electron concentration, from $0.65\mathrm{eV}$ for the highest resistive material up to $0.80\mathrm{eV}$. In the ultraviolet region, electronic interband transitions are detected at 4.84, 5.41, 5.59, and $6.10\mathrm{eV}$, the second being the dominating one, and tentatively assigned in the Brillouin zone.

• Received 28 February 2004

DOI:https://doi.org/10.1103/PhysRevB.70.115217