On the environmental stability of ZnO thin films by spatial atomic layer deposition

Abstract

Undoped and indium-doped ZnO films have been deposited by atmospheric spatial atomic-layer-deposition (spatial-ALD). The stability of their electrical, optical, and structural properties has been investigated by a damp-heat test in an environment with 85% relative humidity at 85 °C. The resistivity of the ZnO films increased during damp-heat exposure mainly due to a sharp decrease in the carrier mobility, while the carrier density and transparency degraded only partially. The increase in resistivity can be ascribed to a degradation of the structural properties of ZnO films, resulting in a higher level of tensile stress, as indicated by x-ray diffraction analysis, and in a reduced near-ultravoilet emission level in their photoluminescence spectra. Al2O3 thin (25–75 nm) films grown by spatial-ALD at 0.2 nm/s are used as moisture barrier to effectively enhance the stability of the electrical and structural properties of the films.

Research Update: Atmospheric pressure spatial atomic layer deposition of ZnO thin films: Reactors, doping, and devices

“…However, a major limitation to the industrial application of any ZnO-based material is that the resistivity increases in hot, humid environments due to structural degradation. 60 This has been overcome by covering the ZnO with a transparent AP-SALD Al 2 O 3 layer (Fig. 8(b)), which acts as a stable moisture diffusion barrier.…”

“…8(b)), which acts as a stable moisture diffusion barrier. 60 The rapid cycle times accessible to AP-SALD make selective area deposition particularly effective. This is because faster cycles reduce the likelihood of the precursors diffusing into the inhibitor.…”

Atmospheric Spatial Atomic Layer Deposition of In-Doped ZnO

“…12 Spatial ALD is emerging as an industrially scalable technique for the deposition of thin film electrodes (e.g., ZnO) and encapsulation (e.g., by Al 2 O 3 thin-films). 13,14 ALD of doped ZnO is typically performed by alternating the selflimiting growth of binary oxide layers (e.g. In 2 O 3 or Al 2 O 3 and ZnO).…”

Recent Advances in Atmospheric Vapor‐Phase Deposition of Transparent and Conductive Zinc Oxide

“…Near‐UV radiation can excite deep‐level defects (e.g., oxygen vacancies) into metastable donor states, thus improving the electrical properties of the film . Photo‐enhanced conductivity is found to be stable in time (for at least 1000 h in air at room temperature) when ZnO is coated by a moisture barrier (e.g., Al 2 O 3 thin film) which prevents a direct exposure to air . The low and stable resistivity value (1.6 × 10 −3 Ω cm), combined with a high transparency in the visible range (90%), enables a possible application of atmospheric PE‐CVD‐grown i ‐ZnO as transparent electrode in electronic devices.…”