Atomic layer deposited AlGaN with different AlN and GaN pulse ratios (2:1, 1:1, and 1:2) was used to prepare AlGaN/GaN Schottky diodes, and their current transport mechanisms were investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements. Under low reverse bias condition, the sample with the pulse ratio of 2:1 was explained by Poole–Frenkel emission and the negative temperature dependence for the sample with the pulse ratio of 1:2 was associated with the acceptor levels in the AlGaN layer. Fast interface traps at 0.24–0.29 eV were observed for the samples with the pulse ratios of 1:1 and 1:2, whereas bulk traps at ~0.34 eV were observed for the sample with the pulse ratio of 2:1. Higher trap densities were obtained from the C–V hysteresis measurements when the pulse ratios were 1:1 and 1:2, indicating the presence of a charge trapping interfacial layer. According to the X-ray photoelectron spectroscopy spectra, the pulse ratio of 2:1 was found to have less oxygen-related defects in the AlGaN layer.
Atomic layer deposited AlGaN on GaN substrate with different thicknesses was prepared and the electron transport mechanism of AlGaN/GaN Schottky diodes was investigated. Above 348 K, both 5 and 10 nm thick AlGaN showed that the thermionic emission model with inhomogeneous Schottky barrier could explain the forward current transport. Analysis using a dislocation-related tunneling model showed that the current values for 10 nm thick AlGaN was matched well to the experimental data while those were not matched for 5 nm thick AlGaN. The higher density of surface (and interface) states was found for 5 nm thick AlGaN. In other words, a higher density of surface donors, as well as a thinner AlGaN layer for 5 nm thick AlGaN, enhanced the tunneling current.
In this study, SnSe powders are nanocoated with ZnO grown by atomic layer deposition (ALD) with different ALD ZnO pulse cycles. Subsequently, the current transport mechanisms of Pt/ZnO-coated SnSe junctions are electrically investigated. A decrease in the current and an increase in the series resistance are observed at 300 K with increasing ZnO pulse cycles (i.e., increasing the thickness of the ZnO layer). The series resistance is similar at 450 K for all samples. The difference in the barrier height for each sample is insignificant, thus indicating that the ZnO coating marginally alters the barrier height at the Pt/SnSe junction. The inhomogeneous Schottky barrier can explain both the forward and reverse bias current conduction. The lowest ideality factor observed for the SnSe sample with ZnO 100 cycles is related to the lowest standard deviation (i.e., the lowest spatial fluctuation of the barrier height). Furthermore, the electrical conductivity is comparable to that of the sample without ZnO coating, thus suggesting that ZnO-coated SnSe by ALD can be considered to improve the thermoelectric device performance.
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 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.
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