Czochralski growth of doped germanium with an applied rotating magnetic field

Abstract

AbstractThe influence of time‐dependent buoyancy convection on the temperature field and the microsegregation during the Czochralski growth of doped germanium was investigated. For physical modelling, experiments with gallium melts have been carried out in the temperature range of 690 to 1000 °C. Growth experiments were performed in a 2 inch crucible. Temperature measurements in the melt revealed convective temperature fluctuations in the range of 1.5 K with a standard deviation of σ=0.3 K. The corresponding frequencies are f≤0.6 Hz. The facility was equipped with a rotating magnetic field (RMF) of Bmax=0.8 mT, adjustable in the range of 5 to 400 Hz. When the maximum field strength was applied, a uniform, azimuthal flow was induced and the germanium melt rotates with 60 rpm. The melt rotation generated by the RMF can completely replace crystal and/or crucible rotation. Growth under an applied RMF results in the lowest microsegregation, compared to the growth without magnetic field / without rotation or to the case when the crystal was rotated but no magnetic field was applied. Increasing the magnetic field strength continuously, the convective temperature fluctuations pass through an intermediated state, where their amplitude becomes even higher, before they are effectively reduced by the RMF.