Atomic Layer Deposition of ZnO for Modulation of Electrical Properties in n-GaN Schottky Contacts

Abstract

ZnO films (5 nm and 20 nm) have been grown on GaN single-crystal substrates by thermal atomic layer deposition (ALD) and the electrical properties of n-GaN Schottky contacts modified by such ultrathin ZnO films have been characterized. Compared with 5-nm-thick ZnO, 20-nm-thick ZnO exhibited a better rectifying nature. The average barrier height and ideality factor at room temperature were extracted to be 0.64 eV and 2.33 eV, and 1.01 eV and 1.16 eV, for 5-nm-and 20-nm-thick ZnO, respectively. These results indicate that both the barrier height and ideality factor were altered effectively by changing the ZnO thickness. The temperature-dependent reverse currentvoltage (I-V) characteristics revealed that tunneling was dominant for the 5nm-thick ZnO. A laterally inhomogeneous barrier was appropriate to explain the forward I-V characteristics for both samples. Based on the parallel conductance method and forward I-V data, a lower interface state density was observed for 20-nm-thick ZnO, implying improved interface quality. These results suggest that the electrical properties of n-GaN Schottky contacts could be easily modulated by changing the ZnO thickness.

Barrier reduction and current transport mechanism in Pt/n-InP Schottky diodes using atomic layer deposited ZnO interlayer

“…Zhu et al deposited ZnO/AlN (220 nm/1.9-11.4 nm) stacks on Ti substrate and found the improved piezo-electric performance [27]. Using ZnO as an IL in Pt/GaN Schottky contacts, we observed the average barrier height (ideality factor) of 0.64 eV (2.33) and 1.01 eV (1.16) for 5 and 20 nm thick ZnO, respectively [16]. All these works suggest the importance of relatively thick ZnO IL ([ 5 nm).…”

“…Because of these reasons, ALD grown ZnO has been used for various devices such as transparent electrode [6,8], active medium for fiber-optic Fabry-Perot interferometer [9], photocatalysis [12], electron transporting layers in organic solar cells [13], and thin film transistor circuits [14]. Most of all, ALD grown ZnO has been employed to modify the interface characteristics in metal/semiconductor (MS) contacts [15,16].…”

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

“…This indicates thermal degradation in the 10 nm-thick ZnO layer at high temperatures. When a 20 nm-thick ZnO IL was used in the Pt/ GaN junction, such thermal degradation was not observed [19]. This implies that the thickness of the ZnO layer is a critical factor in device design.…”

“…To modify the Schottky barrier height in vertical GaN Schottky junctions, the insertion of an ultrathin interlayer (IL) at the metal-semiconductor (MS) interface has been investigated using Al 2 O 3 [17], AlN [18], and ZnO [19]. Most importantly, ZnO/GaN heterojunctions have been investigated as high-sensitivity gas sensors [20,21] and photodetectors [22][23][24] as both GaN and ZnO have a hexagonal structure, a low lattice mismatch (∼1.8%), and similar bandgap energies [25].…”