Computational and experimental studies on band alignment of ZnO/In_xGa_2-xO₃/GaN heterojunctions

The ZnO/GaN heterojunctions are extensively investigated now, owing to their good luminescent properties and devisable capability to form efficient hybrid structures. An electron-blocking layer inserted into heterojunctions can greatly change their properties. In this work, n-ZnO/β-In_xGa_2-xO₃/p-GaN heterojunctions have been successfully formed using atomic layer deposition methods. We show that the doping of In can effectively tune the band edges of the heterojunctions. First-principle calculations reveal that the bandgap of bulk β-In_xGa_2-xO₃ shrinks linearly with the increase in In contents, accompanied by an upward movement of the valence band maximum and a downward movement of the conduction band minimum. As the indium concentrations increase, the valence band offsets show an upward movement at both the In_xGa_2-xO₃/GaN and ZnO/In_xGa_2-xO₃ interfaces, while the conduction band offsets present different trends. A broad, reddish yellow-green emission appears after In doping, which verifies the effect of band alignment. What is more, we show that the amorphization of In_xGa_2-xO₃ can play an important role in tuning the band edge. This work provides access to a series of band offsets tunable heterojunctions and can be used for the further design of direct white light-emitting diodes without any phosphors, based on this structure.