Review Article: Atomic layer deposition of doped ZnO films

Abstract

This article reviews the process-structure-property relationship in doped ZnO thin films via atomic layer deposition (ALD). ALD is an important manufacturing-scalable, layer-by-layer, thin film deposition process that precisely controls dopant type and concentration at the nanoscale. ZnO is an important technological material, which can be doped to modulate structure and composition to tailor a wide variety of optical and electronic properties. ALD doped ZnO is viewed as a transparent conducting oxide for application in solar cells, flexible transparent electronics, and light-emitting diodes. To date, there are 22 elements that have been reported as dopants in ZnO via ALD. This article studies the underlying trends across dopants and establishes generalized relationships for (1) the role of ALD process parameters, (2) the impact of these parameters on the structure of the ZnO matrix, and (3) the impact of dopants on the optical and electrical properties. The article ends with a brief discussion on the limitations of the ALD-based doping scheme, knowledge gaps in the compositional maps, and a perspective on the future of ALD doped ZnO films.

Zinc Oxide Films with High Transparency and Crystallinity Prepared by a Low Temperature Spatial Atomic Layer Deposition Process

“…It was observed that the intensity of (0 0 2) of the sALD-ZnO film increases with substrate temperature due to the lowest surface energy of it. This result indicates the crystal grows along the c axis of wurtzite structure due to (0 0 2) being the closest packing and energetically favorable plane in a wurtzite structure [34]. Therefore, the adatoms gain more energy at a higher temperature to overcome the energy barrier to get to the energetically favorable sites.…”

Zinc Oxide Grown by Atomic Layer Deposition: From Heavily n‐Type to p‐Type Material

“…The review papers on ZnO grown by ALD published to date are mainly devoted to the chemistry of the growth process, crystallinity of the ZnO films, or external donor doping for transparent conductive oxide applications …”

ALD of ZnO:Ti: Growth Mechanism and Application as an Efficient Transparent Conductive Oxide in Silicon Nanowire Solar Cells

“…The obtained films have density values in the range of 5.3 -5.8 g.cm -3 , which is similar to the ZnO density. 9,10 As shown in the Supporting Information (Figure S3), TZO films adopt either a polycrystalline ZnO würtzite structure (n1 ≥ 2) or a ZnTiO3 nanocrystalline one (n1 = 1). 31 All TZO films are transparent in the visible range (transmittance values above 80% in the 300-1200 nm region) with optical gap values between 3.2 and 3.7 eV, which is in agreement to previously reported results.…”

“…5,6 Both undoped and doped zinc oxide have been extensively investigated by ALD. 9,10 Typically, diethylzinc (DEZ) and deionized water (H2O) are used as precursors for Zn and O atom sources. Doped materials are usually obtained by inserting a dopant growth cycle in between an integer number of ZnO cycles, leading to what is referred to as an ALD "supercycle".…”