Effects of Al content on properties of Al–N codoped ZnO films

doi:10.1016/j.apsusc.2004.11.073

Applied Surface Science

Volume 249, Issues 1–4, 15 August 2005, Pages 203-207

https://doi.org/10.1016/j.apsusc.2004.11.073 Get rights and content

Abstract

N doped and Al–N codoped ZnO films were prepared by dc reactive magnetron sputtering with a series of metal–Zn targets having different Al contents. The best p-type electrical properties of codoped ZnO, such as carrier concentration of 2.52 × 10¹⁷ cm⁻³, resistivity of 28.3 Ω cm can be realized by using 0.4 at.% Al target. Results of Hall effect and X-ray photoelectron spectroscopy (XPS) measurements confirm that the presence of Al indeed facilitates the incorporation of N through formation Al single bond N bonds in codoped ZnO. Finally, a new judgement for codoping effect in ZnO is proposed tentatively: the best codoping effect can be realized when the codoped ZnO films possess a closest (0 0 2) d-spacing value to the nominally undoped ZnO.

Introduction

ZnO has been intensively studied as a promising material for blue and ultraviolet light emitting devices because of its wide-band gap of 3.37 eV and large exciton binding energy (60 meV) at room temperature [1]. However, the realization of p-type ZnO is rather difficult due to problems such as self-compensating effect, deep acceptor level, and low solubility of the acceptor dopants [2], [3]. Currently, the development of ZnO-based optoelectronic devices has suffered from one major disadvantage: the lack of good, reproducible, p-type material. Theoretical calculations predicted that nitrogen is the best candidate acceptor for producing p-type ZnO [2]. The codoping method, using acceptors and reactive donors simultaneously, was proposed to increase the solubility of nitrogen in ZnO [4]. Some research groups have made considerable efforts to produce p-type ZnO:N films codoped with Ga or In [5], [6], [7], [8], [9], [10]. However, no successful preparation of p-type ZnO using Al–N codoping method has been reported until our recent work [11], [12]. In this study, ZnO films were prepared by dc reactive magnetron sputtering with a series of targets of different Al contents to examine the effects of Al content on the properties of Al–N codoped ZnO films.

Section snippets

Experiments

ZnO films were prepared on glass and Si (1 0 0) substrates by dc reactive magnetron sputtering. The Al contents in Zn metal targets are 0 at.%, 0.08 at.%, 0.4 at.%, 1 at.% and 4 at.%, respectively. The vacuum chamber was evacuated to a base pressure of 10⁻³ Pa. High purity N₂O (5N) was used as the sputtering gas, the sputtering pressure was maintained at 3 Pa. The substrate temperature was set to 500 °C, the effects of substrate temperature on properties of Al–N codoped ZnO films will be reported

Results and discussion

The film thickness obtained from cross-sectional SEM measurement is about 400 nm. Fig. 1 shows the typical XRD patterns of the as-grown ZnO films using a series of targets with different Al contents (0 at.%, 0.08 at.%, 0.4 at.%, 1 at.% and 4 at.%) on Si (1 0 0) substrates. Only one peak corresponding to the (0 0 2) plane is observed, no Zn₃N₂, Al₂O₃ or AlN peaks are detected obviously. It is suggested that ZnO films exhibit (0 0 2) preferential orientation with the c-axis perpendicular to the substrate.

Conclusions

N doped and Al–N codoped ZnO films with c-axis orientation were prepared by dc reactive magnetron sputtering with a series of metal–Zn targets with different Al contents. Electrical properties as well as (0 0 2) d-spacing value of as-grown ZnO are influenced by Al content evidently. The codoped ZnO films using 0.4 at.% Al target possess the best p-type electrical properties, such as carrier concentration of 2.52 × 10¹⁷ cm⁻³, resistivity of 28.3 Ω cm, and a closest (0 0 2) d-spacing value to the nominally

Acknowledgements

We thank Department of Physics of Zhejiang University for XPS measurements and Professor Zhenguo Ji for XRD measurements. This work was supported by Chinese Special Funds for Major State Basic Research Project G20000683-06 and National Natural Science Foundation of China for Key Project No. 90201038.

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Effects of Al content on properties of Al–N codoped ZnO films

Abstract

Introduction

Section snippets

Experiments

Results and discussion

Conclusions

Acknowledgements

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J. Cryst. Growth

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