Effect of Oxidation Condition on Growth of N: ZnO Prepared by Oxidizing Sputtering Zn-N Film
© The Author(s). 2016
Received: 1 February 2016
Accepted: 16 May 2016
Published: 1 June 2016
Nitrogen-doped zinc oxide (N: ZnO) films have been prepared by oxidizing reactive RF magnetron-sputtering zinc nitride (Zn-N) films. The effect of oxidation temperature and oxidation time on the growth, transmittance, and electrical properties of the film has been explored. The results show that both long oxidation time and high oxidation temperature can obtain the film with a good transmittance (over 80 % for visible and infrared light) and a high carrier concentration. The N: ZnO film exhibits a special growth model with the oxidation time and is first to form a N: ZnO particle on the surface, then to become a N: ZnO layer, and followed by the inside Zn-N segregating to the surface to oxidize N: ZnO. The surface particle oxidized more adequately than the inside. However, the X-ray photoemission spectroscopy results show that the lower N concentration results in the lower N substitution in the O lattice (No). This leads to the formation of n-type N: ZnO and the decrease of carrier concentration. Thus, this method can be used to tune the microstructure, optical transmittance, and electrical properties of the N: ZnO film.
Zinc oxide (ZnO) has a wide direct bandgap of 3.4 eV at room temperature and a high exciton binding energy of 60 meV . Additionally, it also has features of being low cost, non-toxic, stable, and transparent [2, 3]. The ZnO film has become one of the most important semiconductor materials and exhibits a wide potential application in the fields of light-emitting diodes , spintronic device , solar cells , thermoelectric materials [7, 8], and so on. As a semiconductor material, it is important to form a p-n junction and to increase the concentration and mobility of a carrier. Now, it has been a challenge to build a high-efficiency and stable homo ZnO p-n junction  since the carriers are easy to trap at the p-n heterojunction [10, 11]. Although there are reports about the ZnO homo-junction [12–14], a stable and high-efficiency homo-junction is still in the laboratory research stage. The key point is to prepare p-type ZnO and to improve the concentration and mobility of the carrier.
It is generally recognized that the conductivity type of intrinsic ZnO is n-type because there are many donor impurities that exist, such as oxygen vacancy, zinc interstitial, and hydrogen [1, 15]. Furthermore, the concentration and mobility of the carrier in the n-type ZnO is easy to tune by doping the donor impurity (Al, Ga, In, etc.) [16–18]. However, the dopant of acceptor impurity in ZnO is very difficult . Many elements have been selected as the dopant to obtain a more stable p-type ZnO semiconductor, such as N [20, 21], P , As , Sb , Cu , Li , Na , Ag , and Au . In addition, a multi-element co-dopant has also been used to improve the acceptor concentration [29, 30] and to increase the whole concentration so as to compensate the intrinsic defect. But this makes the doping theory become complex. At the same time, the doping result is more difficult to control. Because the elements N and O have similar characters of extranuclear electron structure, ionic radius, and shallow acceptor level, N is one of the more effective dopants for obtaining the p-type ZnO [1–3, 21]. However, the problems of low doping concentration and poor stability still remain for the nitrogen-doped zinc oxide (N: ZnO). The effect of the N dopant and microstructure of the ZnO film on the semiconductor properties should be studied further.
In this study, a method has been developed to prepare N: ZnO by thermal oxidation of the reactive radio frequency (RF) magnetron-sputtering zinc nitride (Zn-N) film. Similar oxidation method has been used in our previous studies [31, 32]. That study focuses on the diluted magnetic semiconductor properties of Co: ZnO film by oxidizing a thermal-evaporated Co/Zn bilayer. In this study, the effect oxidation temperature and oxidation time on the crystal structure, surface morphology, chemical state, transmittance, and electrical properties have been studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS), UV–vis spectrophotometry, and the Hall effect measurement. A new growth model of ZnO was found.
In this study, a Zn-N precursor film was first prepared by reactive RF magnetron sputtering. A high-purity Zn target (99.99 % purity) was used. High-purity N2 (99.99 %) and Ar (99.99 %) were selected as the sputtering gas. The gas partial pressures are 0.3 and 0.5 Pa for N2 and Ar, respectively. The base pressure is <2 × 10−3 Pa, and the working pressure is 0.8 Pa. The sputtering time is 15 min. The distance between the target and the substrate is 100 mm. RF sputtering power is 100 W. The substrate temperature remains at room temperature. Monocrystal Si(100) and quartz are selected as the substrate. The substrates are cleaned in an ultrasonic device for 15 min and in turn in acetone and alcohol bath and then dried by high-pressure Ar blowing.
The Zn-N films were then oxidized to become N: ZnO films at air atmosphere in a heat treatment furnace. The Zn-N specimens were put into the furnace when the temperature reached the oxidation temperature, and then, the N: ZnO films were obtained by oxidizing for the desired time. In this study, two series of oxidation conditions were considered. (1) The samples were oxidized for 60 min at different oxidation temperatures of 300, 400, 450, and 500 °C. (2) The samples were oxidized at 400 °C for different times at 30, 60, and 120 min.
The crystal structure of the films was examined by XRD (DMAX 2400, Rigaku) with a grazing incidence of 1° in 2θ mode with monochromatic Cu Kα1 radiation (λ = 0.154056 nm). Surface morphology was examined by SEM (SUPRA 35, Zeiss). The composition and chemical state of the elements were determined by energy-dispersive X-ray spectroscopy (EDX; Inca, Oxford), XPS (ESCALAB 250Xi, Thermo Scientific), and TEM (2100F, JEOL). Optical transmittance was recorded with a UV–vis spectrophotometer (Lambda 750S, PerkinElmer). The electrical property was investigated by the Hall effect measurements (Ecopia HMS-3000, Korea).
Results and Discussion
Electrical properties of N: ZnO film oxidized at 400 °C for different times
Resistivity (Ω cm)
Carrier mobility (cm2/V S)
Hall coefficient (cm3/C)
9.44 × 1017
6.82 × 1015
1.64 × 1017
However, this kind of growth proposes a new method to control the N: ZnO structure. Furthermore, there is a big difference for the carrier concentration and mobility at different oxidation stages. These provide possibility to prepare p-type ZnO and to improve the concentration and mobility of the carrier. In our study, there are several reasons that lead to the n-type formation and the low carrier concentration and mobility. (1) The substrate temperature maintains at room temperature the deposition of the as-deposited Zn-N film in this study. There are a lot of donor impurities (oxygen vacancy, interstitial zinc, etc.) , which lead to a strong self-compensation effect after oxidation. (2) N content is too low. The lower N concentration results in the lower N substitution in the O lattice (No). This leads to the formation of n-type N: ZnO and the decrease of carrier concentration. In addition, this leads to the electrical properties of the films which are similar with those of the pure ZnO thin film (n-type) and also the lower carrier concentration . Furthermore, the insulating quartz substrate is nonconductive to generate p-type semiconductors .
The N: ZnO film was fabricated by the thermal oxidation of the reactive RF magnetron-sputtering Zn-N film. Oxidation temperature and oxidation time have a significant effect on the crystal structure, surface morphology, and chemical state. The correlation of the optical transmittance and electrical properties with the structure was explored. The results show that the control of oxidation condition of N: ZnO film has made the film exhibit a special growth model. The 400 °C temperature and 120 min time is the best oxidation condition for obtaining a high-quality N: ZnO film. The film can be oxidized completely at this condition. Meanwhile, its transmittance is over 85 % for the visible and infrared light and has a higher carrier concentration. The lower N concentration results in the lower No substitution in the O lattice. This leads to the formation of n-type N: ZnO and the decrease of carrier concentration. This oxidation growth gives an effective method to obtain the needed structure and properties of the N: ZnO film.
This work was supported by the National Natural Science Foundation of China (Grant Nos. 51425401 and 51101034) and the Fundamental Research Funds for the Central Universities (Grant Nos. N140902001).
XQ and GL designed the experiment and analyzed the results. QW and KW instructed the experimental design. GC performed the experiments and the measurements. LX conducted the SEM and TEM analysis. All authors contributed to compiling the manuscript and have approved it for publication.
The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Fan JC, Sreekanth KM, Xie Z, Chang SL, Rao KV (2013) p-Type ZnO materials: theory, growth, properties and devices. Prog Mater Sci 58:874–985View ArticleGoogle Scholar
- Wang M, Ren F, Zhou J, Cai GX, Cai L, Hu YF, Wang DN, Liu YC, Guo LJ, Shen SH (2015) N doping to ZnO nanorods for photoelectrochemical water splitting under visible light: engineered impurity distribution and terraced band structure. Sci Rep 5:12925View ArticleGoogle Scholar
- Stehr JE, Chen WM, Reddy NK, Tu CW, Buyanova IA (2015) Efficient nitrogen incorporation in ZnO nanowires. Sci Rep 5:13406View ArticleGoogle Scholar
- Tsukazaki A, Ohtomo A, Onuma T, Ohtani M, Makino T, Sumiya M, Ohtani K, Chichibu SF, Fuke S, Sgawa Y, Ohno H, Koinuma H, Kawasaki M (2005) Repeated temperature modulation epitaxy for p-type doping and light-emitting diode based on ZnO. Nat Mater 4:42–46View ArticleGoogle Scholar
- Pan F, Song C, Liu XJ, Yang YC, Zeng F (2008) Ferromagnetism and possible application in spintronics of transition-metal-doped ZnO films. Mater Sci Eng R 62:1–35View ArticleGoogle Scholar
- Gonzalez-Valls I, Yu YH, Ballesteros B, Orob J, Lira-Cantu M (2011) Synthesis conditions, light intensity and temperature effect on the performance of ZnO nanorods-based dye sensitized solar cells. J Power Sources 196:6609–6621View ArticleGoogle Scholar
- Nam WH, Lim YS, Choi SM, Seo WS, Lee JY (2012) High-temperature charge transport and thermoelectric properties of a degenerately Al-doped ZnO nanocomposite. J Mater Chem 22:14633–14638View ArticleGoogle Scholar
- Yang Y, Pradel KC, Jing QS, Wu JM, Zhang F, Zhou YS, Zhang Y, Wang ZL (2012) Thermoelectric nanogenerators based on single Sb-doped ZnO micro/nanobelts. ACS Nano 6(8):6984–6989View ArticleGoogle Scholar
- Lim JH, Kang CK, Kim KK, Park IK, Hwang DK, Park SJ (2006) UV electroluminescence emission from ZnO light-emitting diodes grown by high-temperature radiofrequency sputtering. Adv Mater 18:2720–2724View ArticleGoogle Scholar
- Li XY, Chen MX, Yu RM, Zhang TP, Song DS, Liang RR, Zhang QL, Cheng SB, Dong L, Pan AL, Wang ZL, Zhu J, Pan CF (2015) Enhancing light emission of ZnO-nanofilm/Si-micropillar heterostructure arrays by piezo-phototronic effect. Adv Mater 27:4447–4453View ArticleGoogle Scholar
- Schuster F, Laumer B, Zamani RR, Mage’n C, Morante JR, Arbiol J, Stutzmann M (2014) p-GaN/n-ZnO heterojunction nanowires: optoelectronic properties and the role of interface polarity. ACS Nano 8(5):4376–4384View ArticleGoogle Scholar
- Pradel KC, Wu WZ, Ding Y, Wang ZL (2014) Solution-derived ZnO homojunction nanowire films on wearable substrates for energy conversion and self-powered gesture recognition. Nano Lett 14:6897–6905View ArticleGoogle Scholar
- Ko DK, Brown PR, Bawendi MG, Bulovic V (2014) p-i-n heterojunction solar cells with a colloidal quantum-dot absorber layer. Adv Mater 26:4845–4850View ArticleGoogle Scholar
- Li PJ, Liao ZM, Zhang XZ, Zhang XJ, Zhu HC, Gao JY, Laurent K, Wang LY, Wang N, Yu DP (2009) Electrical and photoresponse properties of an intramolecular p-n homojunction in single phosphorus-doped ZnO nanowires. Nano Lett 9(7):2513–2518View ArticleGoogle Scholar
- Rao MSR, Okada T (2014) ZnO nanocrystals and allied materials. Springer India, New DelhiView ArticleGoogle Scholar
- Baek SH, Noh BY, Park IK, Kim JH (2012) Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer. Nanoscale Res Lett 7:29View ArticleGoogle Scholar
- Jun MC, Park SU, Koh J-H (2012) Comparative studies of Al-doped ZnO and Ga-doped ZnO transparent conducting oxide thin films. Nanoscale Res Lett 7:639View ArticleGoogle Scholar
- Thompson RS, Li DD, Witte CM, Lu JG (2009) Weak localization and electron-electron interactions in indium-doped ZnO nanowires. Nano Lett 9(12):3991–3995View ArticleGoogle Scholar
- Dutta S, Chattopadhyay S, Sarkar A, Chakrabarti M, Sanyal D, Jana D (2009) Role of defects in tailoring structural, electrical and optical properties of ZnO. Prog Mater Sci 54:89–136View ArticleGoogle Scholar
- Qin HC, Li WY, Xia YJ, He T (2011) Photocatalytic activity of heterostructures based on ZnO and N-doped ZnO. ACS Appllied Materials & Interfaces 3:3152–3156View ArticleGoogle Scholar
- Zheng M, Wang ZS, Wu JQ, Wang Q (2010) Synthesis of nitrogen-doped ZnO nanocrystallites with one-dimensional structure and their catalytic activity for ammonium perchlorate decomposition. J Nanopart Res 12:2211–2219View ArticleGoogle Scholar
- Kang SJ, Joung YH, Han JW, Yoon YS (2011) Electrical and optical properties of P-doped ZnO thin films by annealing temperatures in nitrogen ambient. J Mater Sci Mater Electron 22:248–251View ArticleGoogle Scholar
- Li WW, Hu ZG, Wu JD, Sun J, Zhu M, Zhu ZQ, Chu JH (2009) Concentration dependence of optical properties in arsenic-doped ZnO nanocrystalline films grown on silicon (100) substrates by pulsed laser deposition. J Phys Chem C 113:18347–18352View ArticleGoogle Scholar
- Suja M, Bashar SB, Morshed MM, Liu JL (2015) Realization of Cu-doped p-type ZnO thin films by molecular beam epitaxy. ACS Appllied Materials & Interfaces 7:8894–8899View ArticleGoogle Scholar
- Chang YT, Chen JY, Yang TP, Huang CW, Chiu CH, Yeh PH, Wu WW (2014) Excellent piezoelectric and electrical properties of lithium-doped ZnO nanowires for nanogenerator applications. Nano Energy 8:291–296View ArticleGoogle Scholar
- Wang LW, Wu F, Tian DX, Li WJ, Fang L, Kong CY, Zhou M (2015) Effects of Na content on structural and optical properties of Na-doped ZnO thin films prepared by sol-gel method. J Alloys Compd 623:367–373View ArticleGoogle Scholar
- Chen Y, Tse WH, Chen LY, Zhang J (2015) Ag nanoparticles-decorated ZnO nanorod array on a mechanical flexible substrate with enhanced optical and antimicrobial properties. Nanoscale Res Lett 10:106View ArticleGoogle Scholar
- Zhang CL, Shao MF, Ning FY, Xu SM, Li ZH, Wei M, Evans DG, Duan X (2015) Au nanoparticles sensitized ZnO nanorod @ nanoplatelet core-shell arrays for enhanced photoelectrochemical water splitting. Nano Energy 12:231–239View ArticleGoogle Scholar
- Shet S, Ahn KS, Deutsch T, Wang H, Nuggehalli R, Yan Y, Turner J, Al-Jassim M (2010) Influence of gas ambient on the synthesis of co-doped ZnO: (Al, N) films for photoelectrochemical water splitting. J Power Sources 195:5801–5805View ArticleGoogle Scholar
- Bu IYY (2015) Sol-gel synthesis of p-type zinc oxide using aluminium nitrate and ammonia. J Ind Eng Chem 28:91–96View ArticleGoogle Scholar
- Li GJ, Wang HM, Wang Q, Zhao Y, Wang Z, Du JJ, Ma YH (2015) Structure and properties of Co-doped ZnO films prepared by thermal oxidization under a high magnetic field. Nanoscale Res Lett 10:112View ArticleGoogle Scholar
- Li GJ, Wang HM, Zhao Y, Wang Q, Wang K, Wang Z (2015) Effect of oxidation temperature and high magnetic field on the structure and optical properties of Co-doped ZnO prepared by oxidizing Zn/Co bilayer thin films. Mater Chem Phys 162:88–93View ArticleGoogle Scholar
- Sinha S, Choudhury D, Rajaraman G, Sarkar SK (2015) Atomic layer deposition of Zn3N2 thin films: growth mechanism and application in thin film transistor. RSC: Advance 5:22712–22717View ArticleGoogle Scholar
- Erdogan NH, Kara K, Ozdamar H, Esen R, Kavak H (2013) Effect of the oxidation temperature on microstructure and conductivity of ZnxNy thin films and their conversion into p-type ZnO: N films. Appl Surf Sci 271:70–76View ArticleGoogle Scholar
- Rusu GG, Gîrtan M, Rusu M (2007) Preparation and characterization of ZnO thin films prepared by thermal oxidation of evaporated Zn thin films. Superlattice Microst 42:116–122View ArticleGoogle Scholar
- Li ZW, Gao W, Reeves RJ (2005) Zinc oxide films by thermal oxidation of zinc thin films. Surf Coat Technol 198:319–323View ArticleGoogle Scholar
- Shao LX, Zhang J (2008) A simple preparation technique of ZnO thin film with high crystallinity and UV luminescence intensity. J Phys Chem Solids 69:531–534View ArticleGoogle Scholar
- Zhang K, Kim SJ, Zhang Y, Heeg T, Schlom DG, ShenW Z, Pan X (2014) Epitaxial growth of ZnO on (111) Si free of an amorphous interlayer. J Phys D Appl Phys 47:105302View ArticleGoogle Scholar
- Kim TW, Kawazoe T, Yamazaki S, Ohtsu M, Sekiguchi T (2004) Low-temperature orientation-selective growth and ultraviolet emission of single-crystal ZnO nanowires. Appl Phys Lett 84:3358–3360View ArticleGoogle Scholar
- Chen R, Zou C, Yan X, Alyamani A, Gao W (2011) Growth mechanism of ZnO nanostructures in wet-oxidation process. Thin Solid Films 519:1837–1844View ArticleGoogle Scholar
- Lin CW, Song YP, Chang SC (2015) Rapid thermal oxidation of zinc nitride film. Jpn J Appl Phys 54:04DH06View ArticleGoogle Scholar
- Wang J, Sallet V, Jomard F, Rego AM, Elamurugu E, Martins R, Fortunato E (2007) Influence of substrate temperature on N-doped ZnO films deposited by RF magnetron sputtering. Thin Solid Films 515:8785–8788View ArticleGoogle Scholar
- Allenic A, Guo W, Chen Y, Katz MB, Zhao G, Che Y, Hu Z, Liu B, Zhang SB, Pan X (2007) Amphoteric phosphorus doping for stable p-type ZnO. Adv Mater 19:3333–3337View ArticleGoogle Scholar
- Ye HB, Kong JF, Pan W, Shen WZ, Wang B (2009) Multi-carrier transport properties in p-typ e ZnO thin films. Solid State Commun 149:1628–1632View ArticleGoogle Scholar