Abstract: Si-doped <511>orientation GaAs crystal was grown by Bridgman method.PBN crucible with a seed well was used and quartz ampoule was adopted to protect the evaporation of As in the process of growth.The doping technology,solid-liquid interface morphology and growth defects were investigated.The twinning was a crucial problem for the pulling-down growth of Si-doped < 511> GaAs crystal.The formation mechanism of the twins was suggested and the growth parameters were optimized.2-inch Sidoped GaAs crystal has been grown successfully and X-ray rocking curve showed that FWHM was about 40 arcsec.

Key words: Si-doped <511>orientation GaAs crystal was grown by Bridgman method.PBN crucible with a seed well was used and quartz ampoule was adopted to protect the evaporation of As in the process of growth.The doping technology,solid-liquid interface morphology and growth defects were investigated.The twinning was a crucial problem for the pulling-down growth of Si-doped < 511> GaAs crystal.The formation mechanism of the twins was suggested and the growth parameters were optimized.2-inch Sidoped GaAs crystal has been grown successfully and X-ray rocking curve showed that FWHM was about 40 arcsec.