Electrical and Optical Properties of Indium Doped Zinc Oxide Films Prepared by Atmospheric Pressure Chemical Vapor Depos
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ELECTRICAL AND OPTICAL PROPERTIES OF INDIUM DOPED ZINC OXIDE FILMS PREPARED BY ATMOSPHERIC PRESSURE CHEMICAL VAPOR DEPOSITION JIANHUA RU AND ROY G. GORDON Department of Chemistry, Harvard University, Cambridge, MA 02138
ABSTRACT Indium doped zinc oxide films have been deposited from diethyl zinc, ethanol and trimethyl 0 indium in the temperature range between 225 C and 450'C in a laminar flow atmospheric chemical vapor deposition reactor. Both doped and undoped films were crystalline. The doped 1 films have electron density up to 9x10 2 0 cm- 3 , conductivity up to 850 91-cm- , and mobility up 2 to 8 cm /Vs. The indium doping increases the average visible absorption from less than 1% to above 20%. The transparency and conductivity of indium doped zinc oxide films are lower than those of fluorine doped films.
INTRODUCTION Zinc oxide is an n-type semiconductor with a hexagonal wurtzite structure and a band gap of 3.3 eV [1]. Zinc oxide and zinc oxide based transparent conductive thin films have gained much attention recently because they have potential applications in liquid crystal displays, energy-efficient windows, and solar cell technology [2-6]. The most common transparent conductive oxide films in use are indium tin oxide and fluorine doped tin oxide films [7, 8]. However, indium and tin are expensive metals; indium and tin based oxide films are more expensive than zinc oxide films. Another disadvantage of indium and tin based oxide films is that they are less stable than zinc oxide films in the presence of a hydrogen plasma which exists in the fabrication process of some optoelectronic devices [3, 9]. Pure zinc oxide films have a low electrical conductivity. Their conductivity can be increased by making the film oxygen-deficient or by doping with foreign atoms such as fluorine [2] or the Group III elements boron [10], aluminum [1, 3, 51, gallium [11], and indium [12, 13]. Doped zinc oxide films have more stable electrical and optical properties than non-stoichiometric films [14]. The deposition of zinc oxide films has been achieved by metalorganic chemical vapor deposition[l, 2, 6, 10], rf magnetron sputtering and reactive sputtering [4, 5, 11, 12, 14], ion beam sputtering [15], spray pyrolysis [3, 13], and sol-gel processing [16]. In this paper we report the deposition of indium doped zinc oxide films from diethyl zinc (DEZ), ethanol and trimethyl indium (TMIn) in an atmospheric pressure chemical vapor deposition reactor. Also discussed is the influence of dopant concentration and deposition temperature on the electrical and optical properties of the films.
EXPERIMENTAL Zinc oxide films were deposited on soda lime glass substrates in an atmospheric pressure chemical vapor deposition system which has been described previously [2]. High purity helium was used as carrier gas for diethyl zinc (DEZ), ethanol and trimethyl indium (TMIn). DEZ bubbler was kept at 25 0 C and its vapor pressure at this temperature is 16.1 Torr. TMIn is a solid at room temperature and it melts at 88'C. The minimum vapor pressure of l
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