Electrical and structural analysis of GaN/ZnO/Ga2O3 bonded interfaces; observation of spinel ZnGa2O4 after annealing

The process of wafer bonding β-Ga2O3 and N-polar GaN with a ZnO “glue layer” was optimized to reduce resistance at the bonded interface. The GaN/ZnO and Ga2O3/ZnO interfaces were studied using TEM, with a focus on the effect of annealing on the ZnO. The thickness of the ZnO “glue layer” was studied to find the optimal behavior and minimum resistance at the interface, with 5 nm determined to give ohmic behavior with resistance lower than the measurement setup could characterize. TEM analysis revealed that the GaN/ZnO interface was sharp before and after annealing, whereas the Ga2O3/ZnO sample had a ZnGa2O4 interlayer that crystallized upon annealing, matching its crystal orientation to the substrate.