On the origin of dislocation generation and annihilation in α -Ga₂O₃ epilayers on sapphire

Epitaxial film quality is critical to the success of high-performance α-Ga₂O₃ vertical power devices. In this work, the origins of threading dislocation generation and annihilation in thick α-Ga₂O₃ films heteroepitaxially grown on sapphire by the mist-CVD technique have been examined by means of high-resolution X-ray diffraction and transmission electron microscopies. By increasing the nominal thickness, screw dislocations exhibit an independent characteristic with a low density of about 1.8 × 10⁶ cm^-2, while edge dislocations propagating along the c-axis are dominant, which decrease down to 2.1 × 10⁹ cm^-2 in density for an 8 μm-thick α-Ga₂O₃ layer and exhibit an inverse dependence on the thickness. In the framework of the glide analytical model, parallel edge dislocations are generated at the interface due to the misfit-induced strain relaxation, while the dislocation glide and coalescence result in the annihilation and fusion behaviors. The optimal thick α-Ga₂O₃ with low dislocation densities may provide a prospective alternative to fully realize α-Ga₂O₃ power devices.