Extra half-plane shortening of dislocations as an origin of tensile strain in Si-doped (Al)GaN

Si doping of (Al,Ga)N layers grown by metalorganic chemical vapor deposition induces an inclination of threading dislocations (TDs). This inclination leads to a change of the extra half-plane size of edge and mixed type dislocations. Depending on the dislocation density and the doping concentration, these effects are accompanied by the generation of tensile strain, which can also lead to crack formation. Several models have been published in the past in order to explain this process. Different models result in opposite TD inclination directions with respect to the extra half-plane position. Therefore, this work examines the correlation between the extra half-plane position and the inclination direction to clarify the origin of the tensile strain increase using scanning transmission electron microscopy. With this approach, it can be unambiguously experimentally verified that Si doping leads to a shortening of the dislocations half-plane. An analysis of in situ wafer curvature measurement proves that the increase of tensile strain in GaN caused by Si doping can be explained by this process. Aside from the inclination caused by Si doping, a TD inclination in undoped GaN layers has been analyzed. Possible explanations for the inclination process are discussed.