A comparative study on the growth of germanium–silicon single crystals grown by the vertical Bridgman and axial heat processing techniques Aidin Dario a , Hasan Ozgen Sicim b , Ercan Balikci b,n a Product Development Department, Ford-Otosan Automotive, 41470 Gebze - Kocaeli, Turkey b Department of Mechanical Engineering, Bogazici University, 34342 Bebek - Istanbul, Turkey article info Article history: Received 30 January 2012 Received in revised form 19 March 2012 Accepted 7 April 2012 Communicated by A.G. Ostrogorsky Available online 19 April 2012 Keywords: A1. Morphological stability A1. Segregation A2. Axial heat processing A2. Bridgman technique B1. Germanium silicon crystals abstract The influence of a submerged baffle on single crystal growth of germanium–silicon is investigated. Twelve crystals have been grown. Eight of them have been grown using the axial heat processing (AHP) technique which makes use of a baffle submerged into the melt. The other crystals have been grown using the conventional vertical Bridgman (VB) technique. Crystals have been grown with 5 and 12 at% silicon at two different velocities, 0.75 and 2 mm/h. Compositional mapping of crystals has been performed by energy dispersive X-ray spectroscopy (EDS). Then, effects of a submerged baffle on the longitudinal and radial solute distribution and interface stability have been discussed. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Recently, Ge–Si alloys have received a widespread interest because of their remarkable potential for optoelectronic [1], solar cell [2], thermoelectric power generation [3,4], and photodetector [5] applications. Ge–Si semiconductor materials are also promis- ing candidates for future Metal-Oxide-Semiconductor (MOS) transistors. Traditionally, MOS transistors are built on bulk Si substrates. However, recent studies [6–8] have shown that strained Si epilayers grown on a relaxed Ge–Si substrate can significantly increase the dopant mobility in Si and so the operating speed and frequency of Si devices. In fact, these Ge–Si substrates are virtual substrates in the sense that they are grown as epilayers on Si substrates. However, a large lattice size mismatch between Si and Ge causes the resultant relaxed Ge-Si virtual substrates to be thick and have poor qualities because of the misfit defects in the epilayers. Bulk Ge–Si substrates stand as a strong substitute for virtual Ge–Si substrates. Recently, there have been studies [8–10] demonstrating that Ge–Si substrates grown using the bulk crystal growth techniques may have several advantages over the virtual substrates. In addition, composition- ally graded bulk grown Ge–Si alloys have been successfully used in X-ray, g-ray, and neutron-diffraction optics [11,12]. Industrial bulk production of high quality Ge–Si single crystals with uniform composition is required to meet the need for Ge–Si substrates in order to maintain the fast paced technological advance in microelectronic industry. However, production of single crystal Ge–Si alloys with uniform composition is very difficult due to the difference in physical properties of the constituent elements, such as melting temperature, density, and lattice parameter. In addition, a wide separation between the solidus and liquidus curves causes the system to be prone to segregation. Bulk growth of this alloy has been studied by several researchers using the Bridgman [13–15], Czochralski [16–18], floating zone [19], and liquid phase diffusion [20]. Marin and Ostrogorsky [21] have investigated the effect of a baffle in the vertical Bridgman (VB) technique on the growth of Ge–Si. Such a growth arrangement is called either submerged heater method (SHM) [21] or axial heat processing technique (AHP) [22]. The current study is undertaken to assess the potential of the AHP technique to grow single crystals of Ge–Si by investigating the effects of a baffle on the shape of solidification interface, solute redistribution, and morphological stability of the grown crystals. In this respect, a comparative study is conducted. Very initial findings of this study have already been published [23]. Two growth modes have been used, VB and AHP that has used a baffle positioned 10 mm and 5 mm above the s/l interface. To the authors best knowledge, there has not been such a comprehen- sive study in the literature on the effects of a submerged baffle on crystal growth from the melt. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2012.04.008 n Corresponding author. Tel.: þ902123597353. E-mail address: ercan.balikci@boun.edu.tr (E. Balikci). Journal of Crystal Growth 351 (2012) 1–8