Abstract: Germanium wafer have been widely used as substrate in space solar cells. In recent years, after the demand for germanium wafer for germanium-based space solar cells increase from 4 inch to 6 inch, the growth of low-dislocation germanium crystals becomes more difficult. This paper designed a double heaters thermal field system suitable for 6 inch low dislocation germanium single crystal by the Cz method, the thermal field distribution in the case of different shapes of main heaters was simulated. The research found that: the thermal field structure of the gradual main heater with the gradual length of L/h=1/2 and the gradual rate ɑ of 65° can obtain the best thermal field distribution, which is conductive to the growth of low dislocation density. It has been verified that the thermal stress of germanium single crystal is reduced, and the dislocation density can be controlled within 310 cm^-2 to 450 cm^-2.

Key words: germanium, single crystal growth, thermal field, heater, temperature gradient, dislocation density