Raman Spectroscopy Studies in InGaN/GaN Epitaxial Layers

Abstract

In this work we studied a set of nominally undoped epitaxial In_xGa_{1- X}N wurtzite films grown on (0001) sapphire substrates. In order to separate the contribution of the strain and indium content in the phonon mode frequency, indium mole fraction was determined using a strain insensitive method, Rutherford backscattering spectroscopy (RBS). Strain was evaluated by comparing the lattice constants measured by X-ray diffraction (XRD) with the relaxed lattice parameters given by Vegard’s law. Samples with comparable indium content, but under different states of strain, were used as reference. This allowed the behaviour of the different Raman shift modes for both strain and composition to be independently established.