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Investigation of Stresses in GaN HEMT Layers on a Diamond Substrate Using Micro-Raman Spectroscopy

Visible and ultraviolet (UV) micro-Raman spectroscopies are used to study the stress in GaN integrated with diamond grown by chemical vapor deposition. Mapping of stress is accomplished across a 75-mm GaN-on-diamond wafer. UV measurements from both sides of the wafer reveal an unexpected gradient between the tensile stress from the free GaN surface (~0.86 GPa) and the GaN/Diamond interface (~0.23 GPa). This gradient is understood through non-uniformities in the material along the growth direction of the layers, with relaxation attributed to threading dislocations. Simulations incorporating stress relaxation in the elastic modulus describe the observed dependence. Measurements from TEM support this conclusion.