title: High electron mobility and low carrier concentration of hydrothermally grown ZnO thin films on seeded a-plane sapphire at low temperature.
abstract: Hydrothermal zinc oxide (ZnO) thick films were successfully grown on the chemical vapor deposition (CVD)-grown thick ZnO seed layers on a-plane sapphire substrates using the aqueous solution of zinc nitrate dehydrate (Zn(NO3)2). The use of the CVD ZnO seed layers with the flat surfaces seems to be a key technique for obtaining thick films instead of vertically aligned nanostructures as reported in many literatures. All the hydrothermal ZnO layers showed the large grains with hexagonal end facets and were highly oriented towards the c-axis direction. Photoluminescence (PL) spectra of the hydrothermal layers were composed of the ultraviolet (UV) emission (370 to 380 nm) and the visible emission (481 to 491 nm), and the intensity ratio of the former emission (I UV) to the latter emission (I VIS) changed, depending on both the molarity of the solution and temperature. It is surprising that all the Hall mobilities for the hydrothermal ZnO layers were significantly larger than those for their corresponding CVD seed films. It was also found that, for the hydrothermal films grown at 70°C to 90°C, the molarity dependences of I UV/I VIS resembled those of mobilities, implying that the mobility in the film is affected by the structural defects. The highest mobility of 166 cm(2)/Vs was achieved on the hydrothermal film with the carrier concentration of 1.65 × 10(17) cm(-3) grown from the aqueous solution of 40 mM at 70°C.
authors: Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, Kuala Lumpur, 54100 Malaysia.
authors: Nurul Azzyaty
authors: NA
authors: Jayah
authors: Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, Kuala Lumpur, 54100 Malaysia.
authors: Hafizal
authors: H
authors: Yahaya
authors: Faculty of Electrical Engineering, Universiti Teknologi MARA, Shah Alam, Selangor 40450 Malaysia.
authors: Mohamad Rusop
authors: MR
authors: Mahmood
authors: Graduate School of Science and Engineering, Ehime University, Ehime, 790-8577 Japan.
authors: Tomoaki
authors: T
authors: Terasako
authors: Department of Electrical Engineering, Nagaoka University of Technology, Kamitomioka-machi, Nagaoka, Niigata 940-2188 Japan.
authors: Kanji
authors: K
authors: Yasui
authors: Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, Kuala Lumpur, 54100 Malaysia.
authors: Abdul Manaf
authors: AM
authors: Hashim
keywords: Carrier concentration; Hydrothermal deposition; Mobility; Seed layer; Zinc oxide