MELT-SOLID INTERFACE SHAPE IN LEC GAAS CRYSTALS - COMPARISON BETWEEN CALCULATED AND EXPERIMENTALLY OBSERVED SHAPES

Two GaAs crystals have been grown by the liquid-encapsulated Czochrals ki (LEG) technique under different experimental conditions with the ai m of revealing the melt-solid interface during growth. The interface s hapes have been evidenced through revealing the growth striations in l ongitudinal cross sections of the ingot, making use of a photoactivate d chemical etching. Measurements of the curvature radii of the various striations have been made by means of a Nomarski-equipped metallograp hic microscope. To investigate the role of the different growth parame ters on the interface shape, the growth processes have been simulated through a model based upon the thermal capillary theory, which is able to describe the temperature field and the interface shapes within the LEC system. The calculated interface shapes have been satisfactorily compared with the experimental ones for undoped crystals. The role of the most significant growth parameters on the interface shape, such as the heater temperature, the crucible-bottom insulation, the encapsula nt volume and the pull rate, have been finally investigated through a sensitivity analysis.