Room Temperature Growth of Indium Tin Oxide Films by Ultraviolet-Assisted Pulsed Laser Deposition
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ROOM TEMPERATURE GROWTH OF INDIUM TIN OXIDE FILMS BY ULTRAVIOLET-ASSISTED PULSED LASER DEPOSITION V. CRACIUN*, D. CRACIUN**, Z. CHEN*, J. HWANG***, R.K. SINGH* *Materials Science & Engineering, University of Florida, Gainesville, FL 32611 "**National Institute for Laser, Plasma and Radiation Physics, Bucharest, Romania ***Physics Department, University of Florida, Gainesville, FL 32611 ABSTRACT The characteristics of indium tin oxide (ITO) films grown at room temperature on (100) Si and Coming glass substrates by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique have been investigated. The most important parameter, which influenced the optical and electrical properties of the grown films, was the oxygen pressure. For oxygen pressure below 1 mtorr, films were metallic, with very low optical transmittance and rather high resistivity values. The resistivity value decreased when using higher oxygen pressures while the optical transmittance increased. The optimum oxygen pressure was found to be around 10 mtorr. For higher oxygen pressures, the optical transmittance was better but a rapid degradation of the electrical conductivity was noticed. X-ray photoelectron spectroscopy investigations showed that ITO films grown at 10 mtorr oxygen are fully oxidized. All of the grown films were amorphous regardless of the oxygen pressure used.
INTRODUCTION Indium tin oxide (ITO) thin films are widely used for optoelectronic devices as they combine a good electrical conductivity with high transparency in the visible range. There are a number of interesting applications such as anode contact in organic light-emitting diodes [1, 2] or coating of flexible polymer substrates for ultralight mobile display panels [3] where the use of a low processing temperature is very important. The use of the pulsed laser deposition (PLD) technique, which has several important advantages [4], has allowed the growth of good quality indium tin oxide (ITO) thin films at relatively low temperatures and even room temperature [58]. Other techniques such as synchrotron radiation ablation [9] or plasma-ion assisted evaporation [10] were also employed to deposit ITO films at room temperature. We investigated the use of an in situ ultraviolet-assisted PLD technique (UVPLD) for the growth of ITO films at room temperature. The UV source photodissociates molecular oxygen and provides ozone and atomic oxygen during the growth [11]. These more reactive gases have been shown to promote the crystalline growth at lower temperatures than those normally used during conventional PLD [ 12]. Moreover, UV+ozone is known to be an effective way to clean organic contaminants from the substrate [ 13, 14], a fact that can also improve the quality of the deposited layers. EXPERIMENT The PLD system employed is presented elsewhere in much more detail [15, 16] and it is only briefly described here. An excimer laser (KrF, k.=248 nm, laser fluence -2 J/cm 2 , repetition rate 5 Hz) was used to ablate ITO targets (99.99% purity). The oxygen pressure was
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