Atomic-layer-deposited Al2O3 and HfO2 on GaN: A comparative study on interfaces and electrical characteristics

Al2O3, HfO2, and composite HfO2/Al2O3 films were deposited on n-type GaN using atomic layer deposition (ALD). The interfacial layer of GaON and HfON was observed between HfO2 and GaN, whereas the absence of an interfacial layer at Al2O3/GaN was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy. The dielectric constants of Al2O3, HfO2, and composite HfO2/Al2O3 calculated from the C–V measurement are 9, 16.5, and 13.8, respectively. The Al2O3 employed as a template in the composite structure has suppressed the interfacial layer formation during the subsequent ALD-HfO2 and effectively reduced the gate leakage current. While the dielectric constant of the composite HfO2/Al2O3 film is lower than that of HfO2, the composite structure provides sharp oxide/GaN interface without interfacial layer, leading to better electrical properties.

Graphical abstractGreat interest has been paid to the GaN-based MOS devices due to their advantages compared with the Schottky-gate GaN devices. In this work, ALD-deposited Al2O3, HfO2, and composite HfO2/Al2O3 films were used as gate dielectrics to passivate the GaN surface. The corresponding electrical and structural characteristics have been systematically studied.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Effective surface passivation of GaN has been demonstrated using ALD-Al2O3 and -HfO2. ► No interfacial layer was formed at Al2O3/GaN interface which remains atomically smooth even after 750oC annealing. ► The interfacial characteristics, in terms of microstructures, roughness, and chemistry were systematically studied using high-resolution t TEM, XRR, and XPS.