Strain was measured in film samples by using X-ray diffraction, Raman and curvature techniques. It was found that, for a Si doping concentration of 2 x 1019/cm3, the threshold thickness for crack formation was about 2.5μm. Transmission electron microscopic observations showed that cracking occurred without dislocation motion, and progressed catastrophically along the low-energy {11▪0} cleavage planes.

Effect of Si Doping on the Strain and Defect Structure of GaN Thin Films. L.T.Romano, C.G.Van de Walle, B.S.Krusor, R.Lau, J.Ho, T.Schmidt, J.W.Ager, W.Götz, R.S.Kern: Physica B, 1999, 273-274, 50-3