ZnO:Al nanostructures synthesized on pre-deposited aluminum (Al)/Si template: Formation, photoluminescence and electron field emission Chiung-Wan Fang a , Jyh-Ming Wu b, ⁎ , Lin-Tsang Lee a , Yeh-Hsin Hsien c , Shen-Chuan Lo c , Chiung-Hsiung Chen c a Department of Applied Mathematics, National Chung-Hsing University, 250, Kuo Kuang Road, Taichung 402, Taiwan b Department of Materials Science and Engineering, Feng-Chia University, 100, Wenhwa Road, Taichung 40724, Taiwan c Material and Chemical Research Laboratories, Industrial Technology Research Institute, Bldg. 77, 195 Section 4 Chung Hsing Road, Chutung, Hsinchu 310, Taiwan Available online 19 June 2008 Abstract Comb-like aluminum (Al) doped ZnO (ZnO:Al) nanostructures were synthesized on Al/silicon substrate by thermal evaporation at 650 °C. A pre-deposited Al layer on the Si substrate was employed to provide the Al dopant into ZnO nanostructures. High-resolution transmission electron microscopy (HRTEM) images displayed that ZnO:Al nanostructures were grown along the [0001] axis. Energy dispersive X-ray spectroscopy (EDS) mapping showed that the Al element was highly scattered and dispersed throughout the ZnO nanostructures. Photoluminescence (PL) spectrum revealed that the ZnO:Al and pure ZnO nanostructures have a blue band emission at 382 nm and 385 nm, respectively. The Al doping did increase the concentration of the oxygen vacancies, therefore a high intensity of green emission band was obtained in ZnO:Al nanostructures as compared to that of pure ZnO nanostructures. The field emission properties of ZnO:Al and ZnO nanostructures were also investigated in this work. The turn-on field of ZnO:Al and pure ZnO nanostructures were found to be 3.8 and 5 V/μm, respectively; the current density was 1 μA/cm 2 . The thresholds field for ZnO:Al and ZnO nanostructures were estimated around 25 and 47 V/μm, respectively; the current density was 1 mA/cm 2 . © 2008 Elsevier B.V. All rights reserved. Keywords: Field emission; Al doped; Nanostructures; Photoluminescence; ZnO; Aluminum 1. Introduction Nanostructures, such as nanowires, nanorods and nanobelts have attracted much attention as semiconductor nanostructured materials having many unique properties with potential applications, such as in gas sensors [1], dye-sensitized solar cells (DSSCs) [2], and optoelectronic devices [3]. Zinc oxide (ZnO) nanostructures have been considered as promising materials for electronic and photonics applications because of their large excitation binding energy of 60 meV with wide direct band gap at 3.37 eV [4]. The ZnO nanostructures are doped with approximate dopant (i.e., gallium, aluminum, indium) [5], which can increase their electrical properties [6–7]. Therefore, a large amount of transparent conducting oxides (TCO), such as indium oxide, tin oxide, and zinc oxide, have been widely studied over the years. However, Al doped ZnO are considered as attractive alternative materials as transparent conducting electrode because they are nontoxic and inexpensive compared with indium tin oxide (ITO). Although many studies have been focused on ZnO:Al thin films by utilizing sputtering process [8–10], one dimensional nanostructured materials of ZnO:Al were rarely investigated. Thermal evaporation is often applied to synthesize the highly crystalline nanostructures. The method is simple and straight- forward, enabling its integrate with the doping process. However, Al is highly oxidized at high temperatures. Therefore, preparation of ZnO:Al nanostructures continue to present challenges. To address this challenge, Hsu et al. [11] reported that the ZnO:Al nanowires can be synthesized by thermal evaporation by introducing a high-voltage source to bombard Available online at www.sciencedirect.com Thin Solid Films 517 (2008) 1268 – 1273 www.elsevier.com/locate/tsf ⁎ Corresponding author. E-mail address: jmwu@fcu.edu.tw (J.-M. Wu). 0040-6090/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.06.037