Evaluation of critical thickness of GaP0.98N0.02 layer on GaP substrate by synchrotron X-ray diffraction topography

Abstract

GaP0.98N0.02 layers having a thickness from 75nm to 600nm are grown on GaP substrates by metalorganic vapor phase epitaxy. Back-reflection X-ray topographs made with a synchrotron radiation of the thick GaP0.98N0.02 layers reveal images of misfit dislocations. The critical thickness of the grown GaP0.98N0.02 layer on GaP substrate is evaluated from the topographs to be about 200nm. The strain relaxation is also observed from high resolution X-ray diffraction curves. X-ray diffraction curves and atomic force microscopy studies indicate that the GaP0.98N0.02 layers with thickness smaller than 200nm possess a very good crystal quality, an atomically smooth surface with a roughness less than 0.3nm and a well-defined interface without misfit dislocations between the layer and the substrate.