Determination of the refractive indices of AlN, GaN, and $AlxGa1−xN$ grown on (111)Si substrates

The refractive indices of several $AlxGa1−xN$ alloys deposited on silicon are determined by ellipsometry and reflectivity experiments at room temperature. The AlGaN layers are grown on (111)Si substrate by molecular-beam epitaxy on top of an AlN/GaN/AlN buffer in order to reduce the strain of the alloy. The Al composition is deduced from energy dispersive x-ray spectroscopy and photoluminescence experiments. The refractive index n and the extinction coefficient k are determined in the 300–600 nm range. For the transparent region of $AlxGa1−xN,$ the refractive index is given in form of a Sellmeier law.