Temperature dependence of the optical properties in hexagonal AlN

We report on the reflectance results of high-quality single crystal AlN thin films at temperature T from 23 to 300 K. With the aid of a detailed procedure developed for analyzing reflection spectra, together with a band tail theory based on calculation of the density of occupied states and carrier-phonon interaction, we have obtained the temperature-dependent optical properties of AlN thin films, such as band gap E-g(T)=6.280-1.700x10(-3)T(2)/(1480+T) eV, absorption coefficient in both the Urbach region alpha(0)=1.02x10(4) cm(-1) and intrinsic absorption region alpha(d)=2.10x10(5)-2.36x10(2)T cm(-1), Urbach band tail parameter E-U(T)=63.5+4.71x10(-3)T(3/2)+1.61 coth(717/T) meV and refractive index. The wavelength- and temperature-dependent refractive index dispersion below the band gap can be described by the Sellmeier equation. Furthermore, we unify the various experimental refractive index data reported in the literature with our refractive index results. These optical properties provide an experimental basis for further theoretical investigation and device design of AlN. (C) 2003 American Institute of Physics.