Band alignment of BeO gate dielectric grown by atomic-layer deposition on AlGaN/GaN HEMTs

•Bandgap of the ALD-BeO film is measured to be 8.2 ± 0.05 eV by REELS.•Valence band offset of the BeO/AlGaN interfaces is determined to be 1.1 ± 0.1 eV by XPS.•Conduction band offset of the BeO/AlGaN is calculated as a very high value of 3.2 ± 0.1 eV.•BeO-gated AlGaN/GaN MOS-HEMT exhibits an on/off current ratio of 107. In this study, we demonstrated the band alignment between a BeO and AlGaN/GaN heterointerface. The bandgap of the BeO film was measured to be 8.2 ± 0.05 eV by reflection electron energy loss spectroscopy. A valence band offset of the BeO/AlGaN interface was determined to be 1.1 ± 0.1 eV by X-ray photoelectron spectroscopy. Based on the spectral analysis result, the conduction band offset was calculated to be 3.2 ± 0.1 eV. When BeO was used as the gate dielectric of an AlGaN/GaN transistor, the on/off current ratio was improved to 107. The results of the band alignment and electrical testing open up opportunities for the application of BeO films to the gate dielectric of GaN-based high-power devices.