Luminescence behavior and compensation effect of N-doped ZnO films deposited by rf magnetron sputtering under various gas-flow ratios of O 2 /N 2 Wei-Min Cho a , Yow-Jon Lin a,n , Chia-Jyi Liu b , Liang-Ru Chen b , Yu-Tai Shih b , Perry Chen a a Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan b Department of Physics, National Changhua University of Education, Changhua 500, Taiwan article info Article history: Received 24 March 2013 Received in revised form 13 August 2013 Accepted 12 September 2013 Available online 19 September 2013 Keywords: ZnO Photoluminescence Raman scattering Defect Conductivity abstract The photoluminescent and electrical properties of N-doped ZnO films fabricated by rf magnetron sputtering under various gas-flow ratios of O 2 /N 2 were examined in this study. The dependence of conduction type on the gas-flow rate of O 2 /N 2 was found. The authors identified a direct correlation between the defect spectral feature and conduction type of N-doped ZnO samples and provided a physical model for producing p-type ZnO. According to these observed results, the authors suggested that p-type conversion of N-doped ZnO may be due to a combined effect of the increased acceptor (substitutional nitrogen in oxygen site, zinc vacancy and interstitial oxygen) density and the decreased donor (oxygen vacancy) density. In addition, synthesis of p-type N-doped ZnO was repeated, suggesting that p-type ZnO can be fabricated with excellent reproducibility by rf magnetron sputtering a ZnO target doped with nitrogen. & 2013 Elsevier B.V. All rights reserved. 1. Introduction ZnO with a direct band gap of  3.4 eV could be a potential candidate for optoelectronic and spintronic applications [1–9]. Clearly understanding the luminescence behavior of ZnO is quite essential for designing optoelectronic and spintronic devices and improving their performance because a large amount of defects in ZnO contribute to the visible emissions and even degrade the near band-edge emission. In addition, the development of ZnO-based optoelectronic devices exploring the exceptional electrical and opti- cal properties of this material has been hindered by the difficulty in realizing high-conductivity p-type ZnO. Therefore, it is import to synthesize p-type ZnO thin films. Many theoretical studies have been undertaken to understand the defects and conductivity of ZnO [10– 15]. Janotti and Van de Walle presented the theory of doping and native defects in ZnO based on density-functional calculations, discussing the stability and electronic structure of native point defects and impurities and their influence on the electrical conduc- tivity and optical properties of ZnO [10]. Yamamoto et al. have investigated the electronic structure of n- and p-type ZnO based on ab initio electronic band structure calculations [11]. P mono-doped and (P, N) codoped ZnO were also investigated by the first-principles calculations [12]. Tian and Zhao found that this significantly reduces the acceptor level of P Zn -4N O complexes and helps improving the p-type conductivity in ZnO, suggesting that a better (P, N) codoped p-type ZnO could be obtained under oxygen-poor condition [12]. Deng et al. used first principles density functional theory to inves- tigate the crystal structure, impurity formation energies, density of states and electronic structure of B–N codoped ZnO [13]. Usually, ZnO films show the n-type electrical property due to native oxygen vacancies (V O ). Thus, the control of native defects as well as extrinsic dopants in the ZnO film is very import. Park et al. suggested that the fabrication and improvement of p-type ZnO films by doping is difficult due to the compensation effect of native n-type carrier with dopants and the low solubility of the acceptor dopants [16]. Nitrogen is one of the dopants for producing p-type ZnO [17–21]. However, the N-doping behavior and conduction mechanisms are still unclear. Based on tight-binding calculations [14], that N would act as shallow acceptor in ZnO, calculations based on density functional theory within the local density approximation or generalized gradient approximation have resulted in an acceptor level (0.4 eV) above the valence-band maximum [15,16]. However, Lyons et al. suggested N is actually a deep acceptor based on first-principles calculations and hence cannot lead to hole conductivity in ZnO [22]. The mechanism of the defect-related conduction type in ZnO has been studied and remains a controversial subject. Experimental work is needed to clarify what defects contribute to the widely observed p-type conductivity in N-doped ZnO. Knowledge of the defect type in Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jlumin.2013.09.029 n Corresponding author. Tel.: 886 4 7232105x3379; fax: 886 4 7211153. E-mail address: rzr2390@yahoo.com.tw (Y.-J. Lin). Journal of Luminescence 145 (2014) 884–887