Microstructural Study of Ultraviolet-Assisted Pulse Laser depoisted Indium Tin Oxide Films

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Microstructural Study of Ultraviolet-Assisted Pulse Laser depoisted Indium Tin Oxide Films Nabil D. Bassim1, Valentin Craciun1, Doina Craciun2 and Rajiv K. Singh2 1 Department of Materials Science and Engineering, University of Florida Gainesville, FL 32611, U.S.A. 2 National Institute for Laser, Plasma and Radiation Physics, Bucharest, Romania ABSTRACT Indium tin oxide is one of the most used transparent conducting oxides. In order to reduce the processing thermal budget and enhance compatibility of these films for such applications as transparent electrodes for solar cells and flat panel displays, lower deposition temperatures are desirable. The addition of a non-thermal energy source during deposition, in this case, a mercury lamp, has the ability to lower the required substrate temperature during processing while increasing the oxygen content of the deposited film through the added contribution of ionized species into the deposited material. We investigated the microstructure of UV-assisted pulsed laser deposited indium tin oxide films. Comparisons between the UV and non-UV films were made in order to judge the effectiveness of the UV radiation in achieving desirable properties. INTRODUCTION Indium tin oxide (ITO) is one of the most widely-used transparent conducting oxides for optoelectronic devices, flat panel displays, and sensors, as it combines good electrical conductivity with high transparency in the visible range due to its degenerative band structure and wide band gap (~3.4 eV). There are many important applications for ITO thin films, such as anode contacts in organic light-emitting diodes or coating of flexible polymer substrates used in ultralight mobile display panels where a low processing temperature is very important. Various types of sputtering techniques were shown to allow the deposition of good quality ITO films even at room temperature [1-4]. These include synchrotron radiation ablation [5], plasma-ion assisted evaporation [6] and electron-beam evaporation [7]. Pulsed laser deposition is another technique that has allowed the growth of good quality ITO films at relatively low temperatures. Ultraviolet (UV) irradiation during thin film deposition by sol-gel [8, 9], sputtering [10], or laser ablation [11] was shown to result in an improvement of crystallinity and surface morphology. We have reported the growth of extremely smooth ITO films (~3Å surface roughness) at low temperatures by using an in situ ultraviolet-assisted PLD technique (UVPLD) during which the substrate is irradiated during the ablation of an ITO target [12]. In this study, we report the effects of UV-assisted PLD of ITO at temperatures ranging from 50°C~220°C on Si (100) and glass substrates on the crystallinity and microstructures of these films. EXPERIMENTAL DETAILS The ITO films were deposited in a PLD system that employs an excimer laser (KrF, λ=248 nm, fluence ~2 J/cm2, repetition rate 5 Hz) to ablate an ITO target (99.999% pure, 10 % weight SnO2). The oxygen pressure during the depositions was set at 10mTorr, which is