Modification of contact properties in Pt/n-GaN Schottky junctions with ZnO and TiO₂/ZnO interlayers

In this study, ZnO (10 nm) and TiO2 (2 nm) were grown on a GaN substrate via atomic layer deposition, and the modified properties of Pt/GaN Schottky diodes with ZnO and ZnO/TiO2 interlayers (ILs) were electrically investigated. The barrier height increased with the ZnO and ZnO/TiO2 ILs; however, the ideality factor increased with the ZnO/TiO2 IL. The reverse-current-voltage characteristics were associated with the Poole-Frenkel emission for all the three junctions. Compared with the Pt/GaN junction, the density of the surface states decreased for the Pt/ZnO/GaN junction but increased for the Pt/ZnO/TiO2/GaN junction. An increase in the ideality factor and a decrease in the barrier height with decreasing temperature were observed at the Pt/GaN and Pt/ZnO/TiO2/GaN junctions. In general, the diode characteristics of the Pt/GaN junction improved owing to the ZnO IL, whereas it degraded owing to the ZnO/TiO2 IL. However, both ZnO and ZnO/TiO2 ILs demonstrate worse diode characteristics at higher temperatures. A thicker ZnO layer (>10 nm) is suggested for improved thermal stability.