Effects of Hydrogen Dilution on ZnO Thin Films Fabricated via Nitrogen-Mediated Crystallization

Abstract

Hydrogenated ZnO thin films have been successfully deposited on glass substrates via a nitrogen mediated crystallization (NMC) method utilizing RF sputtering. Here we aim to study the crystallinity and electrical properties of hydrogenated NMC-ZnO films in correlation with substrate temperature and H2 flow rate. XRD measurements reveal that all the deposited films exhibit strongly preferred (001) orientation. The integral breadth of the (002) peak from the hydrogenated NMC-ZnO films is smaller than that of the conventional hydrogenated ZnO films fabricated without nitrogen. Furthermore, the crystallinity and surface morphology of the hydrogenated NMC-ZnO films are improved by increasing substrate temperature to 400 °C, where the smallest integral breadth of (002) 2θ–ω scans of 0.83° has been obtained. By utilizing the hydrogenated NMC-ZnO films as buffer layers, the crystallinity of ZnO:Al (AZO) films is also improved. The resistivity of AZO films on NMC-ZnO buffer layers decreases with increasing H2 flow rate during the sputter deposition of buffer layers from 0 to 5 sccm. At a H2 flow rate of 5 sccm, 20-nm-thick AZO films with low resistivity of 1.5×10-3 Ω cm have been obtained.

Improvement of m‐plane ZnO films formed on buffer layers on sapphire substrates by mist chemical vapor deposition

“…b, two peaks spaced by 180° were observed for both ZnO and sapphire, since the crystal lattices of m‐plane ZnO and m‐plane sapphire are both rectangular with two‐fold symmetry. The c ‐axes of ZnO and that of sapphire perpendicularly crossed each other on the sapphire substrate, namely ZnO [0001] || sapphire and ZnO || sapphire [0001]. In this φ scan measurement, the ZnO (10–11) and sapphire (11–20) planes were used as the monitoring planes, where Bragg conditions were set to be satisfied.…”

“…and , it was shown that the thickness and crystallographic properties were homogeneous across the substrate, and that the ZnO film was epitaxially grown on the sapphire substrate . In the direction lateral to the sapphire substrate, four small rectangular ZnO lattices are formed on one large sapphire rectangular lattice in the sapphire [0001] direction, indicating domain‐matching epitaxy , where the lattice mismatch in the ZnO [0001] direction is 9.7%, and that in the ZnO direction is 0.1%.…”

“…However, in the case of ZnO, it is not easy to form amorphous layer, and polycrystal ZnO layers are formed even at low temperature. On the contrary, Itagaki et al reported that high‐quality ZnO films were formed by sputtering deposition on ZnO buffer layers with small‐grain polycrystal . This is probably because small‐grain polycrystal of ZnO worked as the appropriate nucleation centers since the AlN low‐temperature buffers for GaN epilayers have similarly many nucleation centers.…”

“…In this study, we improved the crystal quality of the uniform ZnO epitaxial films by introducing ZnO buffer layers , since there are fewer reports on formation of the buffer layers by mist‐CVD. In addition, we focused on the formation of nonpolar m‐plane (10–10) ZnO films on sapphire substrates, since high emission efficiency is expected from quantum‐well layers.…”

Calorimetric Probes for Energy Flux Measurements in Process Plasmas

“…However, the major drawback of adding H 2 is increased etching and reduction of the ZnO films during plasma treatment. More detailed informations about the influence of H 2 addition is given in the literature [86].…”