Anisotropy of electrical and optical properties in β-Ga2O3 single crystals

Anisotropy of electrical and optical properties in $\mathrm{\beta -}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ single crystals has been investigated at room temperature. The conductivity and mobility of the degenerate sample along the direction of b and c axes are ${\text{38\hspace{0.17em}Ω}}^{\text{−1}}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-1}},$ $\text{46\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{2}}{\mathrm{\hspace{0.17em}V}}^{\mathrm{-1}}{\mathrm{\hspace{0.17em}s}}^{\mathrm{-1}},$ and ${\text{2.2\hspace{0.17em}Ω}}^{\text{−1}}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-1}},$ $\text{2.6\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{2}}{\mathrm{\hspace{0.17em}V}}^{\mathrm{-1}}{\mathrm{\hspace{0.17em}s}}^{\mathrm{-1}},$ respectively. The absorption edges of the insulating sample for light polarized E//b and E//c were 4.79 and 4.52 eV, respectively. The rate of the band gap widening with increasing carrier concentration was much larger for E//b than E//c. The origin of these properties are discussed by considering the crystal and electronic structure of $\mathrm{\beta -}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}.$