Role of buried cracks in mitigating strain in crack free GaN grown on Si (1 1 1) employing AlN interlayer schemes

This paper investigates the effect of buried cracks in the AlN interlayer buffer on mitigation of the large, tensile, thermal expansion mismatch strain in the GaN/Si system, which is a key hurdle for achieving crack free GaN epitaxy on silicon. The thermally induced strain is determined by temperature-dependent, high-resolution X-ray diffraction measurements carried out from room temperature up to the growth temperature. It is found that in addition to the balancing effect of compressive lattice-mismatch strain induced by the AlN interlayers, buried cracks in the AlN interlayer region can also relax some of the thermal expansion mismatch strain through elastic distortion at crack edges. The degree of relaxation is dependent on the spacing-to-height aspect ratio of the buried cracks, consistent with prediction of crack-edge-induced relaxation models.