THERMAL-RADIATION AND LOW-TEMPERATURE-VAPOR GROWTH OF HGI2 CRYSTAL INPRODUCTION FURNACE

Heat exchanges in a sealed ampoule in the LTVG (low temperature vapour growth) furnace have been modelled in order to compute temperature fi elds and control the growth of HgI2 crystals from vapour phase at low temperatures. We use a coupled conductive-radiative model to determine the shapes of the source and the crystal at different equilibrium sta tes (i.e. without growth rate). The model involves conductivity anisot ropy in the crystal and radiative exchanges between grey and diffuse s urfaces (source and crystal interfaces, Pyrex walls), which are consid ered as opaque. Internal buoyancy effect is not taken into account as the pressure inside the ampoule is very small. The source temperature is fixed. For different undercoolings, i.e. for different cold finger temperatures, the ''equilibrium'' isotherm between the source/gas and crystal/gas interfaces has been numerically obtained. This ''equilibri um'' isotherm, which is associated with the stop of the growing proces s, gives a crystal shape. This shape is compared with experimental res ults given by the ETH-Zurich group. The model would permit a better un derstanding and control of the future HgI2 crystal growth experiment. The computations are performed using a finite element package (FIDAP).