Characteristics of Ultra violet-Assisted Pulsed Laser Deposited Thin Oxide Films
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V. CRACIUN , R.K. SINGH Department of Materials Science & Engineering, University of Florida, Gainesville, FL 32611 ABSTRACT The properties of thin oxide films such as Y20 3 , ZnO and Bao.5Sr 0 .5 TiO 3 grown using an in situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique have been studied. With respect to films grown by conventional PLD under similar conditions but without UV illumination, the UVPLD grown films exhibited better structural and optical and electrical properties, especially for lower substrate temperatures. They also exhibited a better stoichiometry and contained less physisorbed oxygen than the conventional PLD grown layers. These improvements can be traced to several factors. Firstly, deep UV photons and ozone ensure a better in situ cleaning of the substrate prior to the deposition. Secondly, the presence of more reactive gaseous species like ozone and atomic oxygen formed by photodissociation of molecular 02 promotes the growth of more oxygenated films. Thirdly, absorption of UV photons by adatoms could result in an increased of their surface mobility. All these factors have a beneficial effect upon crystalline growth, especially for moderate substrate temperatures. For optimised growth conditions, the crystalline quality and properties of ultraviolet-assisted pulsed laser deposited films was similar to that of films grown using conventional PLD at substrate temperatures of at least 200 °C higher.
INTRODUCTION Among various techniques for growing thin films, pulsed laser deposition (PLD) hasemerged as one of the most promising due to several important advantages such as stoichiometric transfer, abrupt interfaces, layer by layer growth a.s.o. [1, 2]. One particular advantage that helped PLD to gain its wide spread acceptance is the use of a relatively low substrate temperature during the growth process. However, for many advanced technology applications, a further reduction of the process temperatures is highly desirable. A lower deposition temperature will prevent or at least limit harmful film and/or ambient gas-substrate interaction [3, 4], unwanted substrate interdiffusion processes, and re-evaporation of volatile components [5, 6]. It is also well known from rapid thermal processing practice that substrate temperature non-uniformity and reproducibility is considerably reduced for processing temperatures below 500 °C [7]. With the exception of very few materials, most high quality PLD grown materials, such as high temperature superconductors, ferroelectrics or piezoelectrics, which helped established its reputation, require substrate temperatures in excess of 650 °C. If one wants to lower the processing temperature without adversely affecting the crystalline quality, stoichiometry, and properties, then a non-thermal source of energy and/or a more reactive gaseous atmosphere should be provided during the growth process. Permanent address: Institute of Atomic Physics, Bucharest, Romania
305 Mat. Res. Soc. Symp. Proc. Vol. 623 © 2000 Materials Research Society
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