Melt zone growth of Ge-rich Ge 1-x Si x bulk crystals I. Kostylev, J.K. Woodacre, Y.P. Lee, P. Klages, D. Labrie n Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4R2 article info Article history: Received 19 March 2013 Received in revised form 9 May 2013 Accepted 10 May 2013 Communicated by A.G. Ostrogorsky Available online 18 May 2013 Keywords: A1. Solidification A1. Segregation A2. Melt zone growth A2. Single crystal growth B1. Germanium silicon alloys B2. Semiconducting silicon alloys abstract Melt zone growth of Ge-rich SiGe alloy was performed on 24 mm diameter by 490 mm long feedrods using a resistive furnace. The Si composition along the growth axis of one sample showed a trend where the composition first rapidly decreased, then smoothly transitioned into a plateau-like region, and finally dropped in a Bridgman-like manner near the end of processing. A simple one-dimensional model including full mixing of the melt constituents and an equilibrium Si segregation coefficient given by the phase diagram of SiGe was used to explain the results. The model is in good agreement with the Si composition profile along the growth axis. & 2013 Elsevier B.V. All rights reserved. 1. Introduction SiGe-based heterostructures play an increasing role in the Si microelectronic industry due to the fabrication of RF devices and their integrability with the Si CMOS technology [1]. Research efforts are also being pursued toward the development of Terahertz sources [2–4] and thermoelectric generators using the group IV heterostruc- tures [5]. Their applicability would be expanded if high quality low defect density bulk single crystal Si x Ge 1-x substrates of the desired composition would be available [6,7]. Several crystal growth techniques have been applied to the SiGe binary system but with limited success [8]. The challenge associated with this binary system is related to the large separa- tion between the liquidus and solidus line in the phase diagram, the large temperature difference between the melting point of Ge and Si [9], and large density difference between molten Ge and Si [10,11]. As a result, constitutional supercooling imposes a condi- tion between the temperature gradient in the melt at the solid/ liquid interface and solidification velocity [12]. Furthermore, the SiGe melt stoichiometry does not remain constant with time as solidification proceeds using, for instance, the traditional Bridg- man or Czochralski growth technique [13,14]. Different approaches of the melt zone technique were utilized toward the growth of SiGe alloys. Float zone crystal growth was performed on Si-rich and Ge-rich SiGe alloys using either RF or radiation heating [15–18]. RF heating of 20 mm diameter Si feed rod with a hole drilled along its axis and periodic addition of Ge granules through the hole to the melt during processing was carried out. Single crystal growth of SiGe alloy was obtained but with a non-uniform axial composition [15,16]. Float zone proces- sing using radiation heating of a 8 mm diameter presynthesized Si 0.925 Ge 0.075 feedrod and a 0.5 mm thick Ge disk inserted between the Si seed and feedrod to minimize the transient in composition at the beginning of growth led to a 6 mm wide plateau in composition with [Ge] near 7.5 at%. Although polycrys- tallization occurred, this study pointed to the direction of single crystal growth of homogeneous Si-rich SiGe alloys [18]. A similar approach was used for the float zone single crystal growth of Ge- rich SiGe alloys. For this study, a 10 mm wide plateau in composi- tion, greater than the 8 mm diameter of the feedrod, was observed. Furthermore, this study showed that solutal Marangoni convection due to the free surface of the float zone plays a detrimental role toward interface morphology [17]. Single crystal growth of SiGe alloys was also achieved using the traveling solvent method also referred as the traveling heater method [19–22]. A typical sample consists of a Ge single crystal seed and a Si x Ge 1-x feedrod of the desired composition. Upon partially melting the Ge seed near the seed/feedrod interface, a solvent zone is formed with a Ge-rich SiGe alloy and a melt temperature below the melting temperature of the Si x Ge 1-x feedrod. As the solvent zone is translated slowly along the feedrod, the feedrod is gradually dissolved by the solvent forming a saturated GeSi solution at the dissolution interface. The dissolved GeSi alloy is transported through convection and diffusion to the Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2013.05.012 n Corresponding author. Tel.: +1 902 494 2322; fax: +1 902 494 5191. E-mail address: daniel.labrie@dal.ca (D. Labrie). Journal of Crystal Growth 377 (2013) 147–152