Tuning the electrical properties of the p-type transparent conducting oxide Cu1\u2212xCr1+xO2 by controlled annealing

P Lunca-Popa,D Lenoble,J Afonso,J Crêpellière,R Leturcq,P Grysan

doi:10.1038/s41598-018-25659-3

P Lunca-Popa, D Lenoble + Show 4 more

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https://doi.org/10.1038/s41598-018-25659-3

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Abstract

Off-stoichiometric copper chromium oxide delafossite received lately a great interest due to its high p-type electrical conductivity and adequate optical transmittance in the visible range. However, for a suitable integration in active devices such as p-n junctions, transistors or optoelectronic devices, the electronic properties must be efficiently tailored. Here, post-deposition thermal treatment is proven as an adequate approach for finely controlling the electrical properties of this former degenerate semiconducting material. The energetics of the annealing process are investigated using two different approaches, as a function of the annealing temperature and as a function of the annealing time, allowing the accurate determination of the activation energy of the annealing of defects. By using this method, the electrical carrier concentration was varied in the 1021 – 1017 cm−3 range while the recorded changes in the drift mobility covered three orders of magnitude. Moreover, we demonstrate the ability to accurately manipulate the Fermi level of such materials, which is of great importance in controlling the carrier injection and extraction in optoelectronic active layers.

Highlights

In the field of transparent conductive oxides (TCOs) copper-based delafossite materials are promising candidates as p-type transparent semiconductors closing the gap of optical and electrical properties towards current standard n-type semiconductors
In the case of ZnO31 the activation energy for the annihilation of Frenkel pairs is about 1 eV while the energy barriers for the migration of zinc and oxygen vacancies are 1.4 eV and 2.4 eV, respectively. Based on this quantitative comparison and on our previous microscopic analysis of defects showing the presence of Cu vacancy chains in as-deposited material, we suggest that the changes in electrical conductivities in our system are triggered by Ostwald ripening mechanisms based on the dissolution of shorter chains of vacancies into single Cu vacancies migrating to grain boundaries or longer chained vacancy defects
We proved that the controlled thermal treatment is an efficient approach for controlling electronic properties of Cu0.66Cr1.33O2, a highly conductive p-type transparent oxide

Summary

Introduction

In the field of transparent conductive oxides (TCOs) copper-based delafossite materials are promising candidates as p-type transparent semiconductors closing the gap of optical and electrical properties towards current standard n-type semiconductors (a transmittance greater than 80% in the visible range and an electric conductivity up to 1000 S cm−1). In the present paper we further investigate how a controlled post-deposition thermal treatment can be used as a very effective approach for tailoring electrical properties of Cu0.66Cr1.33O2. Such fine tuning is required for the electrical engineering of transparent devices such as p-n junctions or p-type transistors[15]. The experimental results show that the controlled thermal treatment can be used as a versatile process for controlling the holes concentration, the electrical mobility or even the electronic work function, all being key features for the engineering of electronic properties of transparent solid state devices

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