Stress evolution in thick GaN layers grown by HVPE

This paper investigates the evolution of internal stress in thick GaN layers grown by Hydride Vapor Phase Epitaxy (HVPE) in terms of related strain and bow of the stack GaN layer - substrate. The long-time in-situ thickness and bow measurements were performed during the growth of 3 in. HVPE crystals by using a novel interferometric curvature measurement system. Based on the analysis of the obtained in-situ bow curves, using an elastic model of a two layer system, the presence of an intrinsic negative (tensile) growth strain increasing with the layers thickness could be proven. The inclination of threading dislocations is shown to be a possible root cause for the increasing growth strain. In contrary, the impact of the incorporation of point defects on the lattice deformation is assumed to play a minor role for the appearance of tensile growth strain, at least for typical impurity concentrations in the HVPE environment.