Growth and Characterization of Thermoelectric Mg 2 Si Thin Films
- PDF / 285,335 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 65 Downloads / 439 Views
Growth and Characterization of Thermoelectric Mg2Si Thin Films Thomas C.Hasapis1, Eleni C. Stefanaki1, Anastasios Siozios2, Euripides Hatzikraniotis1, George Vourlias1, Panagiotis Patsalas2, Konstantinos M. Paraskevopoulos1 1 Physics Department, Aristotle University of Thessaloniki, GR- 54124, Thessaloniki, Greece 2 Department of Materials Science and Engineering, University of Ioannina, GR-45110, Ioannina, Greece ABSTRACT In this work, room temperature co-deposition of Mg and Si was used to successfully fabricate Mg2Si thin films on Si substrate by dual cathode magnetron sputtering (DCMS). Films were annealed at 380°C. Various Mg/Si sputtering power ratios have been examined. XRD, SEM and IR reflectivity measurements on grown and annealed films, reveal that annealing is enhancing the formation of crystalline Mg2Si. INTRODUCTION Magnesium silicide (Mg2Si) is a narrow gap semiconductor (Eg~0.3-0.6eV) [1], which crystallizes in the FCC structure and it possesses interesting features such as low density (1.99g/cm3), high melting point (1085ºC) and it is mechanically stable and environmentally friendly as it consists of non-toxic elements in the earth crust. Mg2Si has drawn much of attention as a candidate thermoelectric compound [2]. Bulk Mg2Si is typically prepared by Bridgman method [3] or spark plasma sintering (SPS) technique [4], while, recently mechanical alloying followed by hot pressing has been reported [5]. The n-type material, obtained by alloying with Sn has a high ZT, up to 1.1, at about 900K [2(a)]. At the same temperature range, p-type material, obtained by doping with Bi, presents a ZT of 0.86 (at 862 K) [2(b), 6]. High ZT values and temperature range denote the potential of these materials on energy systems. Many attempts have been made to produce Mg2Si films on Si substrates. The easy oxidation and volatilisation of magnesium are the two main obstacles to obtain high-quality crystalline Mg2Si. In thin films, two main routes are taken; one by co-evaporation of Mg and Si and another by deposition of Mg film on a Si substrate and subsequent annealing, during which Mg react with the substrate and form Mg2Si. Chu et al. reported that a magnesium film deposited at room temperature starts to react with a silicon substrate at a temperature as low as 200 °C [7]. Janega et al. formed Mg2Si by rapid thermal annealing of 100-nm-thick magnesium layers on Si(100), and the magnesium was capped with 500 nm of aluminum to prevent it from evaporating during the reaction [8]. Vantomme et al. obtained Mg2Si thin films by molecular beam epitaxy [9], by evaporation of Mg onto hot silicon substrate (200-5000C) or co-deposition of magnesium with silicon at 2000C using a magnesium-rich flux [10]. Tompa et al formed Mg2Si films by evaporation of Mg on Si (100) substrates, followed by annealing in high temperatures (7000C9000C) [11]. Fewer reports were published about the magnetron sputtering technique for preparing Mg2Si thin films. Xiao et al reported the growth of Mg2Si film after deposition of a thin Mg layer on a Si substr
Data Loading...
