Dependence of the refractive index of AlxGa1-xN on temperature and composition at elevated temperatures

The refractive index of hexagonal AlxGa1-xN at room temperature and its tem perature dependence at elevated temperatures have been determined with high accuracy by spectroscopic ellipsometry. Measurements have been conducted o n samples with aluminum molar fractions ranging from 0% to 65% and at tempe ratures between 290 and 580 K. The refractive index in the transparent spec tral region has been determined as a function of photon energy, using the K ramers-Kronig relations with suitable approximations, and applying a multil ayer model. An analytical expression for the composition and temperature de pendent refractive index in the transparent region, above room temperature, has been obtained. The refractive index has been found to increase with in creasing temperature. The shift of the refractive index is strongest for Ga N and decreases for AlGaN with increasing aluminum molar fraction. The impa ct on the properties of GaN based waveguides is illustrated by a slab waveg uide calculation. (C) 2001 American Institute of Physics.