Interfacial and electrical properties of Al₂O₃/GaN metal–oxide–semiconductor junctions with ultrathin AlN layer

Ultrathin AlN layer deposited by atomic layer deposition (ALD) was employed in Al₂O₃/GaN metal–oxide–semiconductor (MOS) capacitors, and their interfacial and electrical properties were investigated using X-ray photoelectron spectroscopy (XPS) and current–voltage (I–V) and capacitance–voltage (C–V) measurements. XPS analyses revealed that the diffusion of N atoms into Al₂O₃ and the degradation of Al₂O₃ film quality were significant for the thickest Al₂O₃ (10 nm). The sample with a 10-nm-thick Al₂O₃ layer produced the highest leakage current and trap density. These results may result from the deteriorated interface characteristics near the AlN layer caused by long growth time. Therefore, it is suggested that the Al₂O₃ thickness (and optimal growth time) is a key factor in Al₂O₃/AlN/GaN MOS capacitors.