Atomic Layer Deposition of AlN Thin Films on GaN and Electrical Properties in AlN/GaN Heterojunction Diodes

AlN thin films were deposited with different thicknesses (5 and 20 nm) by atomic layer deposition and we explored the electron transport mechanisms in AlN/GaN Schottky junctions. Higher ideality factor and higher m values were observed in the current–voltage plots when the thickness of the AlN was 5 nm. The reverse bias leakage current for 5-nm-thick AlN was explained based on the Poole–Frenkel emission. Capacitance–voltage analysis revealed a higher interface state density for 5 nm thick AlN. These results might be associated with the defective interfacial layer present near the AlN/GaN interface. Because of the strain relaxation, the upper region of the AlN layer was degraded in the case of 20-nm-thick AlN, which may have strongly affected the interfacial properties of the Pt/AlN junction strongly.