Deposition of tin oxides by Ion-Beam-Sputtering
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Deposition of tin oxides by Ion-Beam-Sputtering Martin Becker, Angelika Polity, Davar Feili and Bruno K. Meyer 1st Physics Institute, Justus-Liebig University, Heinrich-Buff-Ring 16, 35392 Giessen, Germany ABSTRACT Synthesis of both p-type and n-type oxide semiconductors is required to develop oxidebased electronic devices. Tin monoxide (SnO) recently has received increasing attention as an alternative p-type oxide semiconductor because it is a simple binary compound consisting of abundant elements. Another phase of the tin oxygen system, SnO2, is of great technological interest as transparent electrodes and as heat-reflecting filters. The preparation of tin oxide thin films has been performed by many different procedures. Radio-frequency (RF) ion-thrusters, as designed for propulsion applications, are also qualified for thin film deposition and surface etching, because different gas mixtures, extraction voltages and RF power can be applied. Tin oxide thin films were grown by ion beam sputtering (IBS) using a 3” metallic tin target. Different aspects of the thin film growth and properties of the tin oxide phases were investigated in relation to flux of oxygen fed into the gas discharge in the ion thruster. Results on thin film growth by IBS will be presented, structural, vibrational and optical properties of the films will be discussed. INTRODUCTION Tin dioxide (SnO2, stannic oxide) is one of the most studied metal oxide semiconductors, which exhibits a wide band gap of 3.8 eV and belongs to the class of transparent conductive oxides. Oxygen vacancies as well as hydrogen and fluorine donors may lead to n-type doping in SnO2 and, accordingly produce a fairly high electrical conductivity. Such properties lead to several technological applications among them gas sensors [1–3] and solar cells [4,5]. Tin monoxide (SnO, stannous oxide) exhibits p-type conductivity with relatively high hole mobilities [6]. The p-type conductivity of SnO was suggested to originate from tin vacancies [7]. Although SnO may be a promising p-type material, the physical and electrical properties of SnO have not been studied in great detail. In the last years SnO has been used in a variety of applications, anode materials for lithium rechargeable batteries [8] and precursor for the production of SnO2 [9] among them. Recently, SnO has received particular attention because of the difficulty in obtaining stable and high quality p-type semiconductors based on other oxides like ZnO or Cu2O. To deposit thin films of tin oxides various techniques have been applied among them sol gel, spray pyrolysis, thermal evaporation, electron beam evaporation, pulsed laser deposition, chemical vapor deposition techniques, molecular beam epitaxy, dc sputtering, RF magnetron sputtering and ion beam sputtering. Among all other deposition techniques, ion beam sputtering [3,10] offers significant advantages over other forms of sputtering [11]. Deposition parameters such as RF power or extraction voltages are not only tunable over a wide range, but can also be varied near
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