Preparation of semiconductive SrTiO 3 thin films by metal-organic chemical vapor deposition and their electrical propert
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Preparation of semiconductive SrTiO3 thin films by metal-organic chemical vapor deposition and their electrical properties Daisuke Nagano, Hiroshi Funakubo, Osamu Sakurai, Kazuo Shinozaki, and Nobuyasu Mizutani Department of Inorganic Materials, Faculty of Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama Meguro-ku, Tokyo 152, Japan (Received 13 September 1996; accepted 27 October 1996)
Insulating epitaxially grown SrTiO3 thin films were prepared on (100)MgO substrates by metal-organic chemical vapor deposition (MOCVD). Semiconductive SrTiO3 thin films were obtained by the rapid cooling after reheating in reduction atmosphere. The microstructure, crystal structure, and electrical properties of these films were investigated. The electrical properties varied by the composition of films and heat-treatment conditions, i.e., the heating temperature, the oxygen partial pressure, and the cooling rate after the annealing. Change of the resistivity of the film was attributed to that of the carrier concentration. Mobility of films was unchanged, and the value was almost the same order of that of bulks. The lowest resistivity of 0.1 V ? cm was obtained when a sample of TiySr 1.0 was heated at 1200 ±C under 10215 Pa of PO2 and then rapidly cooled. This value is similar to that of bulks (100 –1021 V ? cm).
I. INTRODUCTION
SrTiO3 ceramics have been widely used as various electronic devices. The dielectric property of SrTiO3 is widely studied because both the temperature dependency and frequency dependency of the dielectric constant are very small and its dielectric loss is also small.1,2 On the other hand, semiconductive SrTiO3 is also studied as a basic material of boundary layer capacitor and variable resistor with a barrier layer at the grain boundary induced by dopant or reoxidization of only grain boundary.3–6 On the other hand, thin films of SrTiO3 were prepared by different methods for the application of capacitor devices.7–10 However, the study of semiconductive SrTiO3 thin films has been scarcely reported. Gerblinger et al. studied the temperature dependency and oxygen partial pressure dependency of the electrical properties of polycrystalline SrTiO3 thin film deposited on Al2 O3 substrate by rf sputtering,11,12 and applied Al- or Tadoped and undoped SrTiO3 thin films to the gas (CO, CO2 , H2 , H2 O, and CH4 ) sensor at high temperature.13 However, the preparation of semiconductive SrTiO3 thin film with low resistivity similar to the bulk at room temperature has hardly reported. In the present study, we succeeded in preparing epitaxially grown semiconductive SrTiO3 thin film. We already reported on the epitaxially grown semiconductive BaTiO3 thin film by metal-organic chemical vapor deposition (MOCVD) which has low resistivity similar to bulk 1 V ? cm.14 However, semiconductive SrTiO3 has more advantages compared with semiconductive BaTiO3 in the viewpoint of the application to the devices because the resistivity of bulk SrTiO3 is ten times lower than that J.
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