Influence of ZnO Cap Layer Morphology on the Electrical Properties and Thermal Stability of Al‐Doped ZnO Films

Abstract

Herein, ZnO cap layers are prepared by chemical vapor deposition on Al‐doped ZnO (AZO) films and demonstrate a reduction in the electrical resistivity of the films. When prepared at 600 °C, a continuous ZnO cap layer is formed and leads to an increase in a Hall mobility from 22 to 37 cm2 V−1s−1, resulting in a resistivity of 5.1 × 10−4 Ω cm, which is superior to those of nanoparticle and nanorod morphologies formed at lower and higher substrate temperatures, respectively. Furthermore, the continuous ZnO cap layers successfully prevent decreases in the carrier concentration and Hall mobility during annealing at the temperatures of up to 600 °C in air, resulting in a figure of merit (FOM) of 1.6 × 10−2 Ω−1, which is approximately one order of magnitude better than those of uncapped films annealed in Ar. The improvement is due to the cap layer having proper morphology to provide sufficient protection for restructuring of the AZO grain boundaries, thereby reducing the defect density and sacrificing its structural order to suppress Zn desorption in AZO and environmental oxygen migration into AZO during annealing. Using ZnO as a cap layer also reduces the possibility of introducing unexpected band offset at the interface due to extrinsic elements.

High thermoelectric performance of high‐mobility Ga‐doped ZnO films via homogenous interface design

“…Thus, the main reason for the higher electrical conductivities of the ZnO/GZO thin films resulted from larger carrier mobility. Furthermore, to further explore the effects of a buffer layer on mobility, a large amount of experimental data, including unbuffered and buffered ZnO‐based films, was collected from this study and other literature, 7,13,16,22‐24 as shown in Figure 5D. It can be concluded that higher mobility was usually obtained in buffered films when compared with unbuffered films for the same or similar carrier concentration, indicating that a buffer layer can indeed improve the carrier mobility for thin films.…”

“…(A) Electrical conductivity; (B) Seebeck coefficient; (C) Room‐temperature Hall measurement results, including carrier concentration and Hall mobility, alongside the calculated DOS effective mass of all the thin films; and (D) a collection plot showing the carrier concentration and Hall mobility for thin films from this study and the literature 7,13,16,22‐24 [Color figure can be viewed at wileyonlinelibrary.com]…”

Effectively improved piezoelectricity in high-temperature Arrhenius CBT ceramics by modifying potential energy profile and spontaneous polarization

“…Furthermore, the Ps of CBT ceramics is designed to be improved by substitution at B-site. Substituting Nb and Mn ions have been reported to increase d33 of BLSFs by enhancing polarization [23,24], which prompts the selection of dual-ions (Nb2/3Mn1/3) as substitutes for Ti at the B-site. By combining the substitution of (Nb2/3Mn1/3) at B-site and (Na1/2Bi1/2) at A-site in CBT ceramics, significant enhancements in piezoelectricity are achieved through the flatting potential energy profile and the augmentation of Ps.…”

Effects of oxygen flow ratio and thermal annealing on defect evolution of aluminum doped zinc oxide thin films by reactive DC magnetron sputtering

“…Although AZO can readily reach a low ρ ∼ 10 −4 Ω cm, its chemical/thermal stability is typically inferior to other TCOs (e.g. ITO, SnO 2 ), and this is a major issue to be overcome for its wide applications [14,[20][21][22]. The chemical instability of AZO is mainly related with the formation of Zn(OH) 2 and Znbased carbonates at the grain boundaries due to the reaction of the AZO with water and CO 2 molecules from the environment [20], while the thermal instability is linked to diffusion of point defects as well as the formation of new phases and defects [23].…”