Chemical Segregation in Vertical Bridgman Growth of GaInSb Alloys

Abstract

A set of experiments on the solidification of Ga 1-x In x Sb alloys with a large variation of the sample diameter (from 1mm to 10mm), of the growth rate (from 0.7 to 7 μm/s) and of the concentration (from x=0.01 to x= 0.1) is described. The associated radial and longitudinal segregation of the In have been analysed by SIMS or electron microprobe. Numerical simulation of the experiments, taking into account thermal, hydrodynamic and chemical behaviour has been carried out with the help of FIDAP. It is shown from these numerical results that a plateau of concentration can be reached even if a convective loop is present close to the interface, provided that the convection does not extend into the bulk of the liquid. This is in full agreement with the experimental results obtained. Supporting this analysis, in some experiments, a defect in term of verticality of the crucible led to complex 3-D convection involving the whole liquid, and in that case no plateau was obtained. For the radial segregation ΔCR, three regimes of transport are found, characterised by the convective level: - A diffusive one, with a low, constant, ΔCR related to the interface curvature. - A quasi-diffusive one (weak convection) in which ΔCR increases with convection. - A convective one in which it decreases. Measured radial segregations are in good agreement with predictions from the numerical simulations.