Comparison between the relaxation mechanisms of thick (0001) polar and semipolar InGaN layers

In this paper, we investigated the relaxation mechanism of the (0001) polar and semipolar InGaN layer. We observed significantly different tendencies in the relaxation mechanism of both polarities, and each polarity experienced a different relaxation process. Owing to the inclination in the growth orientation of the semipolar layer, misfit dislocations (MDs) occurred at the heterointerface when the strain state of the InGaN layers reached a critical point. Because this result led to gradual relaxation of entire InGaN layers, neither a growth-mode transition (2D pseudomorphic to the 3D domain) nor lateral indium fluctuation occurred. By contrast, the stress-relaxed (0001) polar InGaN layer showed no generation of additional defects at the heterointerface, and the interface area remained strained with respect to the underlying GaN layer. Therefore, because the layer exhibited strong lateral variation in its strain field, growth-mode transition and indium content fluctuation occurred.