&bgr;-Ga2O3single crystals were grown by the floating zone method and their conductivity along thebaxis was controlled from<10−9to38 &OHgr;−1 cm−1by changing the growth atmosphere. By using feed rods doped with Sn, the grown crystal became highly conductive even under oxidative atmosphere. The optical transmission spectra showed that the&bgr;-Ga2O3single crystal with 0.32 mm was transparent in the visible and ultraviolet region, with 20&percent; transmittance at the fourth-harmonic wave of the Nd:YAG laser (266 nm). The band-gap widening was observed with the increasing of the carrier concentration. It is expected that the light of the KrF laser can be transmitted in the heavily doped&bgr;-Ga2O3.©1997 American Institute of Physics.