THERMAL-STRESS ANALYSIS OF CRYSTAL-GROWTH IN A HORIZONTAL BRIDGMAN FURNACE

The boundary element method is used to predict thermal stress profiles in a two-dimensional, rectangular shaped GaAs crystal grown in a hori zontal, two-zone Bridgman furnace. Stress is reported in terms of the excess von Mises yield stress as a criterion that indicates the onset of dislocations. It was observed that the temperature difference betwe en the melting point and the ambient cold zone temperature is directly proportional to the excess stress in the crystal, while the temperatu re driving force in the hot zone has little influence. An increase in the Peclet number and varying length of the adiabatic zone have little effect on the predicted area of dislocations while decreasing the Blo t number results in a larger region of the stress field that violates the von Mises yield stress criterion. The model also predicts dislocat ion-free Ge crystals for operating conditions which give rise to dislo cations in GaAs due to the much higher critical stress of Ge compared with GaAs.