Effects of Al content on properties of Al–N codoped ZnO films
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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2018, Nano EnergyCitation Excerpt :In this regard, doping with N-Al pair seems better than using N-Ga because the corresponding N-Al and Al-O bonds are more stable. Since 2004, Ye group at Zhejiang University carried out a series of experiments on N-Al co-doping to grow p-type ZnO [55–65]. The enhanced N concentration in ZnO was directly evidenced by the depth profiles of N element measured by secondary ion mass spectroscopy (SIMS) [55], as shown in Fig. 2.
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2013, Progress in Materials ScienceStructural and optical properties of Sb-Al co-doped ZnO nanowires synthesized using Nanoparticle Assisted Pulsed Laser Deposition (NAPLD) with Sb as catalyst
2012, Journal of Alloys and CompoundsCitation Excerpt :The deliberate co-doping of donors with acceptors is essential for the enhancement of the solubility of the acceptors with the stabilization of the ionic charge and distributions and the reduction of acceptor binding energies. The co-doping methods simultaneously using group-V acceptors (N and P) and group-III reactive donors (Al and In) were also proposed to increase the solubility of acceptors in ZnO [17–19]. Al:As co-doped ZnO thin film synthesized using magnetron sputtering and Sb:Al co-doped ZnO thin films synthesized using sol–gel also confirms the p-type doping of the samples [20,21].