Liquid Encapsulated Czochralski Growth Of Low Dislocation GaAs

The availability of high quality, large diameter GaAs substrates is key to the success-ful development and production of high-speed GaAs devices and high efficiency GaAs solar cells. The liquid encapsulated Czochralski (LEC) technique has provided a means for pro-ducing large-diameter GaAs.1-4 We wish to report progress in improving the LEC growth process which has resulted in 3-inch GaAs crystals with exceptionally low dislocation densities and reduced propensity for twinning. Undoped, semi-insulating GaAs ingots were grown in a Melbourn high pressure LEC system. We investigated the effects of seed perfection, seed necking, cone angle, melt stoichiometry, ambient pressure, thickness of the B203 encapsulating layer, and diameter control on the dislocation density. The material was characterized by preferential etching and X-ray topography. We show 3-inch diameter substrates can be produced with dislocation densities as low as 6000 cm-2 through proper selection and control of growth parameters. Also, the incidence of twinning can be reduced significantly by growing from slightly As-rich melts.