Strain relaxation and dislocation reduction in AlGaN step-graded buffer for crack-free GaN on Si (111)

GaN growth on Si (111) with reduced dislocation density and wafer bow requires the implementation of strain-compensation techniques to counter the thermal expansion mismatch-related tensile stresses. The ability to design the optimal buffer layer strategy for GaN growth on Si (111) relies on the knowledge of the relaxation processes that occur during the growth. In the AlGaN step-graded buffer, the processes are complex, making it difficult to optimize the layer thicknesses, number of layers and compositions. Here, investigation of the relaxation processes as related to the microstructural evolution within the layers is performed. It is found that the use of xray diffraction measurements of both line width broadening and relaxation reveal the characteristics of the dominant relaxation process of inclination of edge-type dislocation. The methods and results presented here are expected to aid in the optimization for growth of improved quality and wafer bow-free GaN on Si (111). (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim