Interfacial and electrical properties of nanolaminated HfO₂/Al₂O₃ dielectrics on GaN with an AlN interlayer

In this work, we investigated the interfacial properties of AlN/GaN heterostructure with HfO₂/Al₂O₃ (single bilayer) and HfO₂/Al₂O₃/HfO₂/Al₂O₃ (double bilayer) dielectrics prepared by atomic layer deposition (ALD). From capacitance-voltage measurements, significant frequency dispersion was observed for the single bilayer. The interface traps for the double bilayer showed the exponential dependence of trap time constant to the applied voltage, indicating the high quality and uniform interface, whereas the single bilayer deviated from this dependence, revealing the non-uniformity of oxide charges. According to current-voltage measurements, the double bilayer showed much lower leakage current than the single bilayer. X-ray photoelectron spectroscopy measurements showed that Hf-Al-O bonding formed wider region for the double bilayer. For the single bilayer, the outdiffusion of Ga atoms into the AlN layer and the formation of Al-OH were observed more significantly. This work indicates that the double bilayer is a promising dielectric on the AlN/GaN heterostructure.