Band Alignment of Ultra-Wide Bandgap (In_xGa_1-x)₂O₃ and AlN Heterojunction—An XPS Analysis

The heterojunction system comprising InGaO/AlN exhibits remarkable potential for various advanced electronic applications, such as deep UV photodetectors, high-electron-mobility transistors, and high-power electronic devices. The β-(In_0.11Ga_0.89)₂O₃/AlN heterojunction holds significant promise for developing ultrafast responsive deep UV photodetectors with optimal spectral coverage and minimal leakage current. Conversely, the κ-(In_0.15Ga_0.85)₂O₃/AlN heterojunction is expected to achieve a sheet carrier density an order of magnitude greater than that of AlGaN/GaN heterojunctions. Therefore, this research focuses on studying the pulsed laser deposition (PLD) growth parameter optimization and the valence and conduction band offset (VBO and CBO) measurements of β-(In_0.11Ga_0.89)₂O₃/AlN and κ-(In_0.15Ga_0.85)₂O₃/AlN heterojunction to facilitate the development of these next-generation electronic devices. Due to the extreme surface roughness of the AlN wafer, ε-(In_0.15Ga_0.85)₂O₃was formed instead of κ-(In_0.15Ga_0.85)₂O₃. PLD growth optimization experiments revealed that depositing the metastable ε-(In_0.15Ga_0.85)₂O₃requires a moderate temperature, high oxygen pressure, and high laser energy density. The XPS-based Kraut's band alignment approach yielded CBO and VBO values of 3.23 and 1.45 eV for β-(In_0.11Ga_0.89)₂O₃/AlN heterojunction, and 2.482 and 0.87 eV for ε-(In_0.15Ga_0.85)₂O₃/AlN. The reason behind the high VBO observed for β-(In_0.11Ga_0.89)₂O₃/AlN heterojunction could be assigned to the higher valence band edge binding energy of β-(In_0.11Ga_0.89)₂O₃ than the ε-(In_0.15Ga_0.85)₂O₃. These outcomes suggest that the heterojunctions will effectively inhibit carrier leakage, as the high CBO will create a significant obstacle for electron transport through the heterojunction.