Growth of Mg 2 Si 1x Ge x layers on silicon–germanium substrates Yusuke Mizuyoshi a , Ryuji Yamada a , Takuya Ohishi a , Yoshiro Saito a , Tadanobu Koyama b , Yasuhiro Hayakawa b , Takashi Matsuyama c , Hirokazu Tatsuoka a, * a Faculty of Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8561, Japan b Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011, Japan c Pulstec Industrial Co., Ltd., 7000-35 Techno-Land, Hosoe, Inasa, Shizuoka 431-1304, Japan Available online 8 November 2005 Abstract Mg 2 Si 1x Ge x layers were grown on silicon– germanium substrates by heat treatment of the substrates in Mg vapor. The layers were grown by an interdiffusion process between the deposited Mg atoms and the substrates. It has been demonstrated that smooth and continuous layers can be grown with an abrupt layer/substrate interface, and no Kirkendall void is formed. It was found that the Ge contents of the grown layers almost agree with those of the substrates used without any phase separation and/or additional compositional deviation caused by the thermal treatment. D 2005 Elsevier B.V. All rights reserved. Keywords: Silicides; Magnesium; Semiconductors; Diffusion 1. Introduction The Mg 2 Si 1x Ge x (x = 0 to 1) solid solution has attracted much interest as an environmentally conscious semiconductor that consists of non-toxic materials. Mg 2 Si 1x Ge x has a cubic structure with a lattice constant from 0.635 nm (x = 0) to 0.639 nm (x = 1). The Mg-based compounds were originally consid- ered to be one of the thermoelectric materials operating above 200 -C [1–3], and can be used as thermo-photoelectric materials. Band gap tuning is important for use in optoelec- tronic materials. The ternary silicide layers have been grown on Si substrates for Ba 1x Sr x Si, by replacing the alkaline-earth metals [4]. On the other hand, the band gap of the ternary Mg 2 Si 1x Ge x can be controlled by x in Si 1x Ge x from 0.78 eV (x =0) to 0.69 eV (x =1) [5–7]. It should be pointed out that it is difficult to grow Mg-based compound layers, due to high vapor pressure of elemental Mg. Mg atoms are easily evaporated from the substrates, which hinders the formation of the Mg-based compounds. Recently, Mg 2 Si layers have been successfully grown on Si substrates, and the structural properties of the Mg 2 Si layers have been investigated [8,9]. Few studies, however, have reported the growth of the Mg-based ternary silicide layers. In this study, Mg 2 Si 1x Ge x layers were grown using silicon – germanium substrates and the structural property of the layers has been investigated. Moreover, the growth mechanism of the layers is also discussed. 2. Experimental Mg-based ternary silicide layers were grown on polycrystal- line Si 1x Ge x and Ge substrates. The Si 1x Ge x substrates were prepared by Bridgeman’s method, and the chemical composi- tions of the Si 1x Ge x substrates were determined using wavelength-dispersive X-ray spectroscopy (WDS). The pre- pared Si 1x Ge x substrates here have a limited nonhomogeneous spatial distribution in the Ge content, x . One is Si 1x Ge x with x = 0.1–0.2, which is a substrate described as Si 0.8 Ge 0.2 in this report. The other is Si 1x Ge x with x =0.5–0.7, which is a substrate described as Si 0.4 Ge 0.6 . The Mg source and the substrates were placed in a loosely sealed glass container, which was loaded into a vacuum chamber. A schematic illustration of the growth equipment used here is shown in Fig. 1. Both the substrate and the Mg source in the container were then heated and their temperatures were typically maintained at 500 -C for several hours. In this experiment, the substrate temperature was maintained at the same temperature of the Mg source, which is 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.07.331 * Corresponding author. Tel./fax: +81 53 478 1099. E-mail address: tehtats@ipc.shizuoka.ac.jp (H. Tatsuoka). Thin Solid Films 508 (2006) 70 – 73 www.elsevier.com/locate/tsf