Thermal modelling of the casting of CdxHg1−xTe

Abstract The first stage in the cast-recrystallise-anneal process for preparing crystals of Cd x Hg 1− x Te is to quench rapidly to produce a fine-grained polycrystalline ingot. This is then given a high temperature anneal to promote grain growth. Control of the heat loss during the casting stage is crucial in determining the final crystal structure. In order to model heat flows during casting an electrical analogue has been developed and analysed using a computer. The model yields heat flows, temperature distributions (isotherms), and cooling rates. Partial transparency of the silica growth ampoule to radiation is simulated. The effects on cooling rate and isotherm shape of variations in crystal/melt conductivity, gas conductivity and casting rate are described, as is the use of forced cooling of the ampoule base. The isotherms obtained from the model are compared with the dendritic structure seen in cast ingots. Very good agreement between theory and experiment is obtained.