The low thermal stress HP-LEC growth of 75 mm diameter In-DOPED GaAs crystals

Abstract

A study is presented of the effects of various thermal environments in a Melbourn high-pressure liquid encapsulated Czochralski puller on the thermal stress experienced by 75 mm diameter GaAs crystals doped with between 5.4×10 19 to 2.1×10 20cm −3 indium. Approaches investigated for obtaining low thermal stress growth conditions include the use of thick (up to 6 cm) B 2O 3 encapsulating layers, a graphite “top hat” enclosure, and a controllable crystal after-heater and encapsulant heat shield. Of these, the latter configuration appears to yield the lowest thermal stress growth conditions using a 2 cm thick B 2O 3 encapsulant layer. Growths performed using this configuration have yielded low-dislocation (<10 3 cm -2) 75 mm diameter GaAs substrates at an indium doping concentration of 1.1×10 20 cm −3. Finite element fluid dynamics modeling techniques have been employed to determine the effect of the after-heater and encapsulant heat shield on the temperature in the growing ingot and boric oxide encapsulant. These results are compared with those obtained for “conventional” growth conditions.