Influence of substrate annealing on the epitaxial growth of BaTiO 3 thin films by metal-organic chemical vapor depositio
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Influence of substrate annealing on the epitaxial growth of BaTiO3 thin films by metal-organic chemical vapor deposition Cheol Seong Hwanga) and Mark D. Vaudin National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Gregory T. Stauf Advanced Technology Materials, 7 Commerce Drive, Danbury, Connecticut 06810 (Received 26 June 1996; accepted 13 February 1997)
BaTiO3 thin films were deposited by metal-organic chemical vapor deposition at 840 ±C on two differently treated (100) MgO single crystal substrates. One MgO substrate was only mechanically polished and the other substrate was polished and then annealed at 1100 ±C for 4 h in oxygen. Observation by transmission electron microscopy showed that the BaTiO3 thin film deposited on the unannealed substrate was fine-grained and that the whole film was epitaxial (100) in nature. In contrast, the film deposited on the annealed substrate consisted of large, (100)-oriented, epitaxial grains within which were distributed (110)-oriented grains with random in-plane orientations. These differences in BaTiO3 films deposited on differently treated substrates are discussed with reference to the surface structure of the MgO substrate and nucleation kinetics of BaTiO3 thin films on MgO.
I. INTRODUCTION
The ferroelectric oxide BaTiO3 in thin film form is a candidate material for applications such as capacitors,1 infra-red sensors,2 and opto-electronic devices.3 Of these, the opto-electronic devices have the most stringent requirements —the films must be accurately stoichiometric, single phase, and epitaxial. There have been reports on the deposition of epitaxial BaTiO3 thin films by laser ablation4 and metal-organic chemical vapor deposition (MOCVD).5–9 Deposition of an epitaxial BaTiO3 thin film is a complicated process because many deposition parameters must be precisely controlled. Since perovskite BaTiO3 is a line compound and there are several other crystalline and amorphous phases in the Ba–Ti–O system, the composition must be controlled very carefully to obtain a single-phase, epitaxial film. Advantages of MOCVD over other deposition techniques include uniform coating of large areas with complex three-dimensional geometries at high throughput. The ability to control many of the deposition parameters independently during MOCVD is one of the main strengths of the technique. However, the effect of the important deposition parameters (e.g., substrate temperature, gas phase composition, and gas flow rates) and materials parameters (e.g., metal-organics used, nature of the substrate) on the composition and microstructure of the deposited film need to be clearly
understood for the advantages of MOCVD to be fully realized in a commercial setting. A study has been made of the effect of deposition temperature and substrate surface treatment on the epitaxial growth and optical properties of BaTiO3 thin films deposited on single crystal MgO by MOCVD.8,9 Films were deposited at substrate temperatures ranging from 700 ±C
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