Application Properties of ZnO and AZO Thin Films Obtained by the ALD Method

Barbara Swatowska,Tomasz Stapiński,Gabriela Lewińska,Rafał Pietruszka,Marek Godlewski,Halina Czternastek,Wiesław Powroźnik,Bartłomiej S Witkowski

doi:10.3390/en14196271

Barbara Swatowska, Tomasz Stapiński + Show 6 more

Open Access

https://doi.org/10.3390/en14196271

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Abstract

The thin layers of ZnO and ZnO: Al (Al doped zinc oxide—AZO) were deposited by the atomic deposition layer (ALD) method on silicon and glass substrates. The structures were deposited using diethylzinc (DEZ) and deionized water as zinc and oxygen precursors. A precursor of trimethylaluminum (TMA) was used to introduce the aluminum dopant. The present study of ALD-deposited ZnO and AZO films was motivated by their applications in photovoltaics. We attempted to expose several properties of such films. Structural, optical (including ellipsometric measurements) and electrical investigations were performed. We discussed the relations between samples doped with different Al fractions and their properties.

Highlights

Zinc oxide (ZnO) is one of the most popular semiconductor materials with a wide band gap equal to 3.27 eV at room temperature, with an exciton binding energy of60 meV, but most of all, with a free electron concentration regulated in a wide range, up to 1020 cm−3 [1,2,3]
Layers obtained by the atomic layer deposition (ALD) method on silicon substrates
ALD technology enables precise control of Al content in aluminum doped zinc oxide (AZO) layers for films grown with Al fractions of up to 3%

Summary

Introduction

60 meV, but most of all, with a free electron concentration regulated in a wide range, up to 1020 cm−3 [1,2,3] Due to such properties, ZnO-based thin layers can be used as the transparent conducting oxide (TCO) in solar cells and in ultraviolet light emitters [1,2,3]. Even though ITO layers are still superior—they have high conductivity and optical transparency in the wide range of the solar spectrum [4,5]—their price becomes too high due to the increasing price of indium. This fact started an active search for alternative. One of the most promising alternative TCO materials is ZnO, in particular when doped with Al (AZO), Ga (GZO), In (IZO) or F (FZO) [4]

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