COMPUTER MODELING OF TEMPERATURE AND STRESS DISTRIBUTIONS IN LEC-GROWN GAAS CRYSTALS

Temperature and thermal stress distributions have been modelled in a LEC GaAs crystal at various stages of growth using boundary conditions which allow for radiation into the argon atmosphere and thermal conduction into the boric oxide encapsulant. Results have been obtained as a function of oxide conductivity, oxide depth, ambient temperature above the oxide, and shape of the GaAs solid-melt interface shape. Heat losses into the encapsulant are important, both in reducing thermal stresses in the early stages of growth and in increasing them once the conical region has fully formed. It is shown that in both situations, a reduction in thermal stress can be effected by increasing the depth of oxide and the temperature of the environment it loses heat to. The convex crystal-melt interface shapes that occur in practice are not optimum for reducing stress: flatter interfaces should be aimed for. These results are discussed in the context of other studies.