Measurements were made of stresses in GaN epitaxial layers grown onto 6H–SiC and α-Al2O3 substrates. The biaxial stresses ranged from 1.0GPa (tensile) to -1.2GPa (compressive). Stress determined from curvature measurements, obtained using phase-shift interferometry microscopy, compare well with measurements using accepted techniques of X-ray diffraction and Raman spectroscopy. Correlation between X-ray diffraction and Raman measurements of the E22 phonon gives a Raman-stress factor of –3.4/cmGPa. Phase-shift interferometry microscopy was applied to temperature-dependent stress measurements of the GaN films. Variations found in the stress–temperature coefficient correlate well with threading dislocation densities. A phenomenological model was developed which described the thermal stress of the epitaxial GaN as a superposition of that for ideal GaN and the free volume existing in the layers due to the threading dislocations. The model describes well the observed dependence.

Dependence of the Stress–Temperature Coefficient on Dislocation Density in Epitaxial GaN Grown on α-Al2O3 and 6H–SiC Substrates. I.Ahmad, M.Holtz, N.N.Faleev, H.Temkin: Journal of Applied Physics, 2004, 95[4], 1692-7