Abstract: The liquid or gaseous substances, such as hydrogen or trichlorosilane, enntered in the gas-phase deposition of silicon may contain n-type doping impurities which can be removed by adduct formation with silicon, titanium or tin halides. The impurities can be liberated from the adducts by thermal treatment and finally removed. The halides left behind are capable of again forming adducts and are again used to remove the impurities. The process can consequently be operated cyclically and is remarkable for the low quantity of chemicals required and for its ecological harmlessness.