Granular polycrystalline silicon and production thereof

A process for producing a granular polycrystalline silicon in a fluidized bed reactor, comprising:

• fluidization of silicon seed particles by a gas flow in a fluidized bed which is heated by a heating apparatus,
• addition of a silicon- and halogen-containing reaction gas resulting in pyrolytic deposition of elemental silicon on heated surfaces of the seed particles,
• forming the granular polycrystalline silicon, with removal from the reactor of particles whose diameter has grown as a result of deposition and an offgas comprising hydrogen halide, and metered addition of fresh seed particles,
• wherein:
• (a) a concentration of hydrogen halide in the offgas is determined as a controlled variable;
• (b) and a rate of the metered addition of fresh seed particles and a heating output of the heating apparatus are controlled as manipulated variables, in order to keep the hydrogen halide concentration in the offgas within a defined range during operation;
• (c) the granular polycrystalline silicon has a chlorine content of 10-40 ppmw;
• and (d) the granular polycrystalline silicon comprises particles having a convexity of 0.850-1.000.