Strain relaxation of InGaN/GaN Strain relaxation of InGaN/GaN by formation of V-pits by formation of V-pits
Abstract
Formation of V-pit defects is a commonly observed phenomenon in InGaN epilayers.[1] However, the exact mechanism of V-pit formation remains unclear in some aspects. TEM images from numerous studies show, that the V-pits emerge from the point, where a threading dislocation from GaN substrate intersects the boundary between the substrate and the layer.
Nevertheless, it was not confirmed, that all the V-pits and all the threading dislocations at interface act in this way.[2] Moreover, X-ray diffraction (XRD) experimental data exhibit very low degree of plastic relaxation of InGaN layers, and it is still matter of controversy, if the V-pits creation can relieve elastic energy sufficient for the strain relaxation.[3, 4] We present results of numerical simulations of elastic strain fields and X-ray reciprocal space maps (RSM) in comparison with XRD and AFM experimental data yielded from a series of MOVPE-grown samples. We used samples with InGaN layer thickness of 10 - 135 nm and 10-20\% In content, for which high-resolution XRD reciprocal space maps were measured.
These experimental RSMs were compared with simulations based on kinematic XRD theory and on strain field model, considering linear elastic behavior of materials. The results were verified by analysis of AFM images taken from the surface of the samples.
Our study provides an evidence, that the V-pits have major influence on strain relaxation in InGaN/GaN.