Codoping and Interstitial Deactivation in the Control of Amphoteric Li Dopant in ZnO for the Realization of p-Type TCOs.

Alessandra Catellani,Arrigo Calzolari

doi:10.3390/ma10040332

Abstract

We report on first principle investigations about the electrical character of Li-X codoped ZnO transparent conductive oxides (TCOs). We studied a set of possible X codopants including either unintentional dopants typically present in the system (e.g., H, O) or monovalent acceptor groups, based on nitrogen and halogens (F, Cl, I). The interplay between dopants and structural point defects in the host (such as vacancies) is also taken explicitly into account, demonstrating the crucial effect that zinc and oxygen vacancies have on the final properties of TCOs. Our results show that Li-ZnO has a p-type character, when Li is included as Zn substitutional dopant, but it turns into an n-type when Li is in interstitial sites. The inclusion of X-codopants is considered to deactivate the n-type character of interstitial Li atoms: the total Li-X compensation effect and the corresponding electrical character of the doped compounds selectively depend on the presence of vacancies in the host. We prove that LiF-doped ZnO is the only codoped system that exhibits a p-type character in the presence of Zn vacancies.

Highlights

Transparent conducting oxides (TCOs) are a special class of materials that combine electrical conductivity with transparency for visible light [1]
We can realistically assume that the undoped ZnO samples intrinsically include structural defects, such as vacancies and dislocations, whose amount strictly depends on the growth techniques
In order to decouple the complex interplay between the existing defects and the dopants, we considered four possible initial hosts each including zero or one neutral point defect, namely: an oxygen (VO ), a zinc (VZn ), and a

Summary

Introduction

Transparent conducting oxides (TCOs) are a special class of materials that combine electrical conductivity with transparency for visible light [1]. They play a key role in optoelectronic applications [2] such as photovoltaics [3], touch-screen sensors, low emissivity windows, liquid crystal display (LCD) devices, plasma and organic light emitting diode (OLED) displays, and smart windows. Prototype TCO semiconductors are impurity-doped ZnO, In2 O3 , SnO2 and CdO, and multi-component oxides consisting of combinations of them. Al doped ZnO (AZO) TCO thin films are the materials of choice for most of the present applications. The requirement of transparency corresponds to wide bandgap Eg > 3.0 eV

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Conclusion