On the origin of dislocation generation and annihilation in α-Ga_2O_3 epilayers on sapphire

摘要

Epitaxial film quality is critical to the success of high-performance alpha-Ga2O3 vertical power devices. In this work, the origins of threading dislocation generation and annihilation in thick alpha-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 x 10(6) cm(-2), while edge dislocations propagating along the c-axis are dominant, which decrease down to 2.1 x 10(9) cm(-2) in density for an 8 mu m-thick alpha-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 alpha-Ga2O3 with low dislocation densities may provide a prospective alternative to fully realize alpha-Ga2O3 power devices.