Chemical segregation in vertical Bridgman growth of GaInSb alloys

A set of experiments on the solidification of Ga1-xIn4Sb alloys with a larg e variation of the sample diameter (from 1mm to 10mm), of the growth rate ( from 0.7 to 7 mu m/s) and of the concentration (from x=0.01 to x= 0.1) is d escribed. 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, hydro dynamic and chemical behaviour has been carried out with the help of FIDAP. It is shown from these numerical results that a plateau of concentration c an 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. T his 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 Delta C-R, three regimes of transport are found, characterised by the convective level: A diffusive one, with a low, constant, Delta C-R related to the interface c urvature. A quasi-diffusive one (weak convection) in which Delta C-R increases with c onvection. A convective one in which it decreases. Measured radial segregations are in good agreement with predictions from th e numerical simulations.