* Corresponding author. Present address: Center for Micro- gravity and Materials Research, The University of Alabama in Huntsville, Huntsville, AL 34899, USA. Tel.:#1-256-890-6944; fax: #1-256-890-6050. E-mail address: ostroga@email.uah.edu (A.G. Ostrogorsky). Journal of Crystal Growth 217 (2000) 360}365 Segregation of Ga in Ge and InSb in GaSb P.S. Dutta, A.G. Ostrogorsky* Department of Mechanical Engineering, Aeronautical Engineering and Mechanics, Rensselaer Polytechnic Institute, Troy, NY 12180, USA Received 21 January 1999; accepted 20 April 2000 Communicated by R.S. Feigelson Abstract Axial and radial segregation of (i) Ga in Ge and (ii) InSb in GaSb has been evaluated in crystals grown by the submerged heater method. The values of di!usion coe$cients obtained by "tting the Tiller's equation to the initial transients in composition are signi"cantly lower than the values in the literature, obtained by using shear cells with capillaries.  2000 Elsevier Science B.V. All rights reserved. PACS: 71.55.Eq; 81.10.Fq; 81.30.Fb; 64.75.#g Keywords: Ge; GaInSb; Segregation; Submerged ba%e; Di!usion coe$cients 1. Introduction Dopant and alloy segregation is a key phenom- enon occurring during directional solidi"cation of semiconductors. Segregation leads to non-uniform spatial electrical and optical properties and alloy composition in the wafers obtained from various sections of the crystal. The compositional homo- geneity in the growing crystal is strongly a!ected by melt convection near the solid}liquid interface. Uniform distribution of impurities (having equilib- rium segregation coe$cient kO1) is achieved only when all impurities, which are absorbed at the melt}crystal interface, are continuously replenished from the bulk melt. Steady replenishment can occur only if the growth rate R is constant, melt convec- tion is steady and predictable, and the concentra- tion of impurities in the bulk melt remains constant during growth [1]. These conditions are not satis- "ed during normal freezing on earth because of buoyancy-driven convection. Steady-state segrega- tion was reported only in a few space-grown crys- tals [2]. More recently, directional solidi"cation under terrestrial conditions by (a) application of magnetic "elds during crystal growth [3}5] and (b) employing a submerged heater in the melt near the growth interface [6], the required condi- tions for steady-state growth by normal freezing and zone solidi"cation techniques have been met. Strong reduction in convective interference with segregation was demonstrated by the latter technique in a large number of experiments with various materials system [7}9]. In particular, exceptionally uniform steady-state segregation was recently obtained in Te-doped GaSb by using large seeds in conjunction with an un-powered 0022-0248/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 4 8 3 - 8