Layer transfer of bulk gallium nitride by controlled spalling

摘要

Successful wafer-scale layer transfer from high-quality 2-in. diameter bulk gallium nitride substrates was demonstrated using the Controlled Spalling technique. The crystal quality of both the as-fractured bulk substrate and the spalled GaN film was assessed using transmission electron microscopy analysis, and the defect density was below the detection limit (mid 107cm~(-2)) for both samples. By using the experimentally determined critical conditions for tensile stress and thickness of the Ni stressor layer, an effective fracture toughness K_(IC) of 1.7 MPa √m could be calculated for [0001] fracture using the Suo and Hutchinson mechanical model. The resulting in-plane contraction of the GaN film after spalling permitted a novel method for measuring film strain without knowledge of the elastic properties of the material. This was used to measure the Raman E)2(high) peak shift coefficient of Δω(cm~(-1)) = 1411ε which, when converted to a stress coefficient (2.95 cm~(-1)/GPa), was in agreement with only one other literature value.