beta -Ga2O3 is a transparent oxide and intrinsically an insulator. Doping allows the variation of the conductivity for both p- and n-type over a wide range. There are a number of potential applications in optoelectronics such as insulating or conductive window material, or as a substrate. Consequently, the influence of doping on the electrical and optical properties is an issue of crucial importance for pushing this material forward to applications. We report on the successful growth of undoped. Ge- and Ti-doped beta -Ga2O3 single crystals by the floating zone technique. Both electrical and optical properties were characterized. (C) 2001 Elsevier Science B.V. All rights reserved.