This study reports a non-destructive method of measuring the residual strain in the GaN epilayer grown on sapphire substrate by micro-Raman spectroscopy. Operating in confocal mode this method allows a depth-dependent measurement of residual strain in the epitaxial layer without prior treatment of the sample. This approach to measurement of residual strain is demonstrated on GaN epitaxial films grown by both MOCVD and H-MOVPE. In the case of MOCVD grown films, the biaxial strain energy was found to vary from 0 (GaN surface) to 5.0 kJ/mole (GaN/sapphire interface), but in the case of H-MOVPE grown samples the strain energy varied from 6.5 kJ/mole -hydrostatic strain (GaN surface) to 25.0 kJ/mole -biaxial strain (GaN/sapphire interface), indicating that the surface layer of the N-terminated H-MOVPE material is not free from strain. Estimates are given for the curvature of substrate, lattice parameter of epitaxial layer, and the interface shear modulus.

We report on the measurement of stress in bulk, free‐standing GaN templates under external bending using micro‐Raman scattering. A 488 nm Ar‐ion laser beam was scanned in a cross‐sectional geometry across the GaN template held under external stress conditions. Our experiment showed that the top half of the bulk GaN was under ∼73 MPa of tensile stress while the bottom half of the GaN template was under 40 MPa of compressive stress when bent by a press screw. This data is very helpful to understand both the optical and mechanical properties of bulk GaN and for calibrating and optimizing GaN‐based pressure sensors. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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