Vertical gradient freeze growth of GaAs with a rotating magnetic field

Results on the growth of GaAs by the vertical gradient freeze (VGF) technique with a rotating magnetic field (RMF) are presented. The experiments were aimed at influencing the heat flux at the liquid-solid interface in a predefined way to reduce its bending. Si doped crystals with a diameter of two inch were grown. Variation of the heat flux is directly evaluated from dopant striations artificially produced by means of pulses of the RMF itself. The results are compared with those obtained by global modelling of the furnace as well as by analytical and numerical treatment of the melt flow. The concave deflection of the interface is found to decrease considerably under forced convection and at certain aspect ratio a wavy shape is observed. The RMF induced redistribution of axial thermal gradients resulting in a temporary variation of the growth rate that becomes lower in the outer region of the melt and higher in the central part is measured directly. The experimental results agree well with the numerical
computations.