Effect of hydrogen plasma treatment on the luminescence and photoconductive properties of ZnO nanowires
- PDF / 1,710,687 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 99 Downloads / 320 Views
1206-M13-03
Effect of hydrogen plasma treatment on the luminescence and photoconductive properties of ZnO nanowires Yanbo Li, Ryohei Uchino, Takero Tokizono, Alexander Paulsen, Miao Zhong, Masaki Shuzo, Ichiro Yamada, and Jean-Jacques Delaunay Department of Mechanical Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
ABSTRACT ZnO nanowires with strong green emission synthesized by chemical vapor deposition were treated using hydrogen plasma. The effect of hydrogen plasma treatment was studied by means of photoluminescence and photoconductivity. A strong passivation of the green emission and a significant enhancement of the near band edge emission were found after the hydrogen plasma treatment. The conductivity of the nanowires in dark was increased by more than 3 orders of magnitude. The photoconductivity also increased after the hydrogen plasma treatment. The observed changes in the luminescence and photoconductive properties of the ZnO nanowires were likely caused by hydrogen atoms occupying both oxygen vacancies and interstitial sites. INTRODUCTION Zinc oxide (ZnO) is a wide-band-gap semiconductor with unique piezoelectric, optical, and electrical properties which has many technological applications [1, 2]. ZnO almost always shows strong n-type conduction due to unintentional doping. The origin of the n-type conductivity has been widely debated. It was traditionally thought that the native defects, including zinc interstitials and oxygen vacancies, should be responsible for the n-type conductivity [3, 4]. However, Vanheusden et al. [5, 6] proved through their experiments that the oxygen vacancies should not be the source of donor since the free carrier concentration was much larger than the concentration of oxygen vacancies. A first-principles study showed that the energy levels of oxygen vacancies and zinc interstitials were too deep in the band gap to contribute to the conductivity [7]. Therefore, the n-type conduction of ZnO must be attributed to impurities that are unintentionally incorporated. Hydrogen was then proposed as a cause of doping in ZnO [8]. The influence of hydrogen on defects in ZnO bulk crystals or powders were studied using cathodoluminescence (CL) [9], photoluminescence (PL) [10], and Raman [11]. ZnO nanowire (NW) is a good starting material for study the effect of hydrogen. Because of their small size and large surface-to-volume ratios, hydrogen can be easily incorporated into ZnO NWs. Besides, ZnO NWs can be synthesized with controllable properties using simple methods. The understanding of the effect of hydrogen in ZnO NWs is also very important for their future device applications. In this report, the effect of H2-plasma treatment on the luminescence and photoconductive properties of ZnO nanowires was studied. ZnO NWs with strong green
emission were first grown by chemical vapor deposition (CVD). The fabricated sample consisted of ZnO NWs bridged between thick ZnO electrodes, which are used to record the electrical properties of the bridged NWs [12-14
Data Loading...
