A modified vapor pressure-controlled Czochralski (VCz) method is reported which employs a diving bell around the growing crystal, Semi-insulating (SI) GaAs crystals with a diameter of 160 mm and an overall length up to 220 min were grown from melts of up to 23 kg, and compared with similar-sized crystals grown using a standard liquid-encapsulati on Czochralski (LEC) process. Optimization of the VCz process was assisted by global numerical simulations. A slightly convex growth interface has been found to be the most suitable one for achieving a relatively low EPD of similar to 104 cm(-2), with an associated reduction in the probability of dislocation bunching. The carbon concentration of the crystals was controlled down to values Of 10(14)cm(-3). The electrical properties, including the EL2 degrees content are discussed. (c) 2007 Elsevier B.V. All rights reserved.