Journal of Crystal Growth 310 (2008) 214–220 Effects of the Li-evaporation on the Czochralski growth of g-LiAlO 2 Bozˇa Velicˇkov a,Ã , Anna Mogilatenko b , Rainer Bertram a , Detlef Klimm a , Reinhard Uecker a , Wolfgang Neumann b , Roberto Fornari a a Institute for Crystal Growth (IKZ), Max-Born-Str. 2, 12489 Berlin, Germany b Institute for Physics, Humboldt University Berlin, Newtonstr. 15, 12489 Berlin, Germany Received 26 June 2007; received in revised form 31 August 2007; accepted 5 September 2007 Communicated by R.S. Feigelson Available online 12 October 2007 Abstract Two-inch-diameter g-LiAlO 2 single crystals were grown from the melt by Czochralski method. The crystals were examined by optical methods, high-resolution X-ray diffraction and transmission electron microscopy (TEM). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the Li/Al ratio in the residual melts. The Li-evaporation from both melt and grown crystal is the main problem in the g-LiAlO 2 growth and has to be controlled by acting on the vertical temperature gradient. Shallow gradients increase the Li-evaporation from the crystal surface resulting in boules with a milky rim. On the other hand, steep gradients may induce cracks in the boule and enhance the Li 2 O escape from melt with consequent variation of the composition. ICP-OES investigations reveal that melt compositions can vary in the range from 46.5 to 50 mol% Li 2 O to obtain transparent LiAlO 2 crystals. Beyond this value, the formation of inclusions inside the crystals is probable. We have established an optimized growth assembly, which allows remaining the melt composition stoichiometric. The as-grown crystals exhibit defects like subgrains, twins and a core of voids and fine-grained inclusions. The latter could be characterized by TEM as submicron LiAl 5 O 8 crystallites. r 2007 Elsevier B.V. All rights reserved. PACS: 61.72.Ff; 77.84.Bw; 81.10.Fq Keywords: A1. Characterization; A2. Czochralski method; A2. Single crystal growth; B1. Gamma-LiAlO 2 ; B1. Lithium compounds 1. Introduction During recent years, several research groups succeeded to grow epitaxial GaN layers on single-crystal g-LiAlO 2 wafers [1–5]. Compared to a-Al 2 O 3 , the most common substrate material for GaN, the distinct advantages of g-LiAlO 2 are the option to grow m-plane GaN layers and the self-separation of thick GaN films from the g-LiAlO 2 substrate (Table 1). These can be utilized as freestanding GaN wafers for homoepitaxy [4,5]. Beside the physical and chemical properties, economical aspects also play an important role. Thus, a comprehensive research in this field should be focused on the development of a reproducible cost-effective single crystal growth technology. g-LiAlO 2 melts congruently and consequently the Czochralski (CZ) technique was chosen to obtain single crystals with high perfection [7]. The CZ method is well established and it offers, in principle, the possibility of achieving high-yield and large-diameter single crystals hence lowering the costs of the process. However, in the case of g-LiAlO 2 , this is difficult to realize as previous studies showed that its growth from melt is complicated. First, Cockayne and Lent [7] described the growth of g-LiAlO 2 by CZ method as a problematic process due to the loss of the volatile alkali component, probably escaping as Li 2 O. Their 16-mm-diameter crystals showed in depen- dence on the growth rate a core of voids and inclusions or characteristic of cellular structures grown under conditions of constitutional supercooling. Nevertheless, in their study, it was possible to obtain crystals with a high degree of optical perfection. Recently, Chou et al. [8,9] reported the growth process for 2-in.-diameter g-LiAlO 2 single crystals ARTICLE IN PRESS www.elsevier.com/locate/jcrysgro 0022-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2007.09.046 Ã Corresponding author. Tel.: +49 30 6392 3020; fax: +49 30 6392 3003. E-mail address: velickov@ikz-berlin.de (B. Velicˇkov).