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

Al"2O"3, HfO"2, and composite HfO"2/Al"2O"3 films were deposited on n-type GaN using atomic layer deposition (ALD). The interfacial layer of GaON and HfON was observed between HfO"2 and GaN, whereas the absence of an interfacial layer at Al"2O"3/GaN was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy. The dielectric constants of Al"2O"3, HfO"2, and composite HfO"2/Al"2O"3 calculated from the C-V measurement are 9, 16.5, and 13.8, respectively. The Al"2O"3 employed as a template in the composite structure has suppressed the interfacial layer formation during the subsequent ALD-HfO"2 and effectively reduced the gate leakage current. While the dielectric constant of the composite HfO"2/Al"2O"3 film is lower than that of HfO"2, the composite structure provides sharp oxide/GaN interface without interfacial layer, leading to better electrical properties.