Synthesis and control of conductivity of ultraviolet transmitting β-Ga2O3 single crystals

Abstract

$\mathrm{\beta -}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ single crystals were grown by the floating zone method and their conductivity along the $b$ axis was controlled from ${\text{<10}}^{\text{−9}}$ to ${\text{38\hspace{0.17em}Ω}}^{\text{−1}}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-1}}$ by 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 $\mathrm{\beta -}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ single crystal with 0.32 mm was transparent in the visible and ultraviolet region, with 20% 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 $\mathrm{\beta -}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}.$