Determination of the band gap of indium-rich InGaN by means of photoacoustic spectroscopy

Photoacoustic (PA) measurements have been performed on a series of InxGa1-xN thin films grown with x > 50%. In order to illustrate the usefulness of this technique, these measurements have been compared with the results obtained by the following conventional techniques: photoluminescence, transmittance and contactless electroreflectance. Amongst all these techniques, only PA spectroscopy exhibited signal without the undesired Fabry-Perot interferences arising from the thin film and buffer layer. By accurately assessing the strain state and composition of our samples, we were able to study the compositional dependence of the band gap of our epilayers. Our results show that a bowing parameter of 1.43 eV successfully describes the compositional dependence of the band gap of InGaN.