Carrier Compensation Mechanism of Highly Conductive Anatase Ti 0.94 Nb 0.06 O 2 Epitaxial Thin Films
- PDF / 140,375 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 43 Downloads / 202 Views
1074-I05-08
Carrier Compensation Mechanism of Highly Conductive Anatase Ti0.94Nb0.06O2 Epitaxial Thin Films Hiroyuki Nogawa1, Taro Hitosugi1, Hideyuki Kamisaka2, Kouichi Yamashita2, Akira Chikamatsu3, Kouhei Yoshimatsu3, Hiroshi Kumigashira3, Masaharu Oshima3, Syoichiro Nadao4, Yutaka Furubayashi4, Yasushi Hirose1, Toshihiro Shimada1, and Tetsuya Hasegawa1 1 Department of Chemistry, University of Tokyo, 7-3-1, Hongo, Bunkyoku, Tokyo, 113-0033, Japan 2 Department of Chemical System Engineering, University of Tokyo, 7-3-1, Hongo, Bunkyoku, Tokyo, 113-0033, Japan 3 Department of Applied Chemistry, University of Tokyo, 7-3-1, Hongo, Bunkyoku, Tokyo, 1130033, Japan 4 Kanagawa Academy of Science and Technology, 3-2-1, Sakado, Takatsuku, Kawasaki, 2130012, Japan ABSTRACT We investigated electrical conduction of anatase Ti0.94Nb0.06O2 (TNO) epitaxial thin films in relation to oxygen defects generated by post-annealing. Annealing of TNO in oxygen was found to cause dramatic decreases in ne. Resonant photoemission spectroscopy measurements revealed that a deep acceptor state just above the top of valence band evolves, synchronized with the decrease of ne. We proposed that the acceptor state originates from interstitial oxygen atoms combined with Nb dopants and compensates electron carriers. INTRODUCTION Transparent conducting oxides (TCOs) have been established as essential materials for opto-electronic devices, such as flat-panel displays, light-emitting devices and solar cells [1]. Among variety of TCOs, Sn-doped In2O3 (ITO) has been widely utilized, because of its low resistivity (ρ ~ 2 x 10-4 Ω cm) [2] [3] and high optical transmittance in the visible light region [3] [4]. However, indium, being a major element of ITO, has a problem of unstable supply due to the rapidly expanding worldwide consumption. Moreover, rapid advance in opto-electronics requires additional properties of TCOs, such as high refractive index and high transmittance at infra-red region, which are difficult to realize by using existing TCO materials, activating researches searching for new TCOs. We have recently reported that anatase Ti0.94Nb0.06O2 (TNO) thin films epitaxially grown on SrTiO3(100) substrate by using pulsed laser deposition (PLD) show low ρ of 2.1 x 10-4 Ωcm at room temperature and a high internal transmittance of ~95% in the visible region.[5] We have also demonstrated excellent conductive properties with ρ = 4.6x10-4 Ω cm even in polycrystalline TNO films deposited on glass [6] [7]. In these successive studies, we have pointed out that the resistivity of TNO is influenced by oxygen partial pressure (Po2) during film growth. Very recently, Zhang et al. reported that the carrier concentration (ne) of TNO strongly depends on Po2 [8]. These suggest that oxygen defects play a significant role in electrical conduction of TNO.
In this paper, we report on transport properties of TNO films post-annealed under various atmospheres with different Po2. Annealing of TNO films in oxygen atmosphere was found to drastically suppress ne. Based on th
Data Loading...
