Band offset and electrical properties of ErZO/β-Ga₂O₃ and GZO/β-Ga₂O₃ heterojunctions

The fabrication of ohmic contacts on wide bandgap semiconductors, such as β-Ga₂O₃, is difficult as the scarcity of metals with low-enough work function. The insertion of n⁺-doped metal oxide layer between metal and the β-Ga₂O₃ layers are effective for improving the ohmic behaviour. β-Ga₂O₃, Erbium doped ZnO (ErZO), and Gallium doped ZnO (GZO) films with high crystallinity were deposited by pulsed laser deposition. The band offsets and electrical properties of ErZO/β-Ga₂O₃ and GZO/β-Ga₂O₃ heterojunctions were investigated, which revealed the nested gap (type I) structures. The conduction band offsets were determined to be 0.88 eV for ErZO and 0.96 eV for GZO, and their corresponding valance band offsets were found to be 0.46 eV and 0.16 eV. In addition, the difference of the work functions between ErZO and β-Ga₂O₃ was 0.05 eV; and 0.16 eV between GZO and β-Ga₂O₃. Solar blind UV detector having fork electrode structure of as-grown β-Ga₂O₃/ErZO/Ti/Au structure showed good ohmic performance and have superior detector performance comparing with the other two electrode structures, which was ascribed to ErZO's low band offset and small work function difference with β-Ga₂O₃. The present result provides an option for fabricating ohmic contact on β-Ga₂O₃ without the need for post-growth annealing.