Transparent Oxide Semiconductors Obtained by PLD
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1074-I07-12
Transparent Oxide Semiconductors Obtained by PLD Anna Vila, Antonis Olziersky, Joaquim Font, Teresa Andreu, Erik Koep, and Juan Ramon Morante Electronics Department, University of Barcelona, Marti i Franques 1, Barcelona, 08028, Spain ABSTRACT In this work we studied metaloxide films such as ZnO, In2O3-ZnO, In2O3-ZnO-ZrO2 and Ga2O3-In2O3-ZnO deposited by pulsed laser deposition on fused silica substrates at room temperature. Optical transmission measurements in the ultra violet – visible region showed that oxygen-rich atmospheres during deposition help to obtain more transparent films in the optical region while improving overall UV absorption transition related to the band gap. Less resistive films are produced in oxygen-rich atmospheres but an increase of oxygen pressure leads to higher resistivity films. INTRODUCTION Wide band-gap semiconductors have been increasingly used in applications such as solar cells, optoelectronic devices, flat-panel displays and various sensors. A very interesting group of materials are the transparent conducting oxides (TCOs) such as indium tin oxide (ITO), which has been used for electrodes in liquid crystal display industry, in solar cells, and gas sensors [14]. ZnO has also been used successfully in chemical sensors and UV detection applications [5,6]. Lately, compound TCOs have drawn the attention of the research community as last-years efforts [7,8] showed that they could be used as semiconductors for the fabrication of electronic components in a way where a complete device could be fabricated solely by transparent metaloxide materials [9]. These materials combine satisfying transparency (>80%) in the optical range and electrical properties that can be controlled by the incorporation of different multi-component oxides. Another very important aspect of these materials is the ability to provide similar electrical performance regardless their state, crystalline or amorphous [10]. This aspect provides the opportunity of adopting low-temperature processes by breaking the trade-off rule that low temperature processing sacrifices device performance, and thus opening the road to fabrication of high performance devices on flexible substrates. The strategy behind the synthesis of such materials is the incorporation of heavy (n>4, with n the primary quantum number) post-transition metals such as Sn, Ga, In, in an effort to form a widely dispersed conduction-band minimum, so that a higher overlap of the ns orbitals from neighboring atoms can occur, thus increasing mobility [11]. Zinc oxide, even though it does not belong to post-transition metals, due to small Zn-Zn distance, favors dispersing the conduction-band minimum. For the fabrication of devices, high quality films have to be produced with high carrier mobility and controllability of carrier concentration. A number of techniques have been used for the deposition of TCOs, such as magnetron sputtering, chemical vapor deposition, spray pyrolysis, reactive thermal evaporation and pulsed laser deposition (PLD) [12-16]. PLD us
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