Abstract
We investigate strain and composition of epitaxial single layers of wurtzite InxGa1-x N (0<x<0.25) grown by MOCVD on top of GaN/Al2O3 substrates. It was shown that significant inaccuracies may arise in composition assessments if strain in InxGa1- xN/GaN heterostructures is not properly taken into account. Rutherford backscattering spectrometry (RBS) measures composition, free from the effects of strain and with depth resolution. Using X-ray diffraction (XRD) we measured both a- and c- parameters of the strained wurtzite films. By measuring both lattice parameters and solving Hooke’s equation, a good estimation for composition can be obtained from XRD data. The agreement between RBS and XRD data for composition allows reliable values for perpendicular (ezz) and parallel strain components (exx to be determined. RBS and depth resolved cathodoluminescence (CL) measurements further indicate that the indium content is not uniform over depth in some samples. This effect occurs for the most strained layers, suggesting that strain is the driving force for compositional pulling.
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