We report the results of a comprehensive study on the structural, electronic, and optical properties of ${\mathrm{Ga}}_2{\mathrm{O}}_3$ in its ambient, monoclinic $\left(\beta \right)$ and high-pressure, hexagonal $\left(\alpha \right)$ phases in the framework of all-electron density functional theory. In both phases, the conduction band minimum is at the zone center while the valance band maximum is rather flat in the $k$ space. The calculated electron effective mass $m_e^{*}∕m_0$ comes out to be 0.342 and 0.276 for $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ and $\alpha \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$, respectively. The dynamic dielectric function, reflectance, and energy-loss function for both phases are reported for a wide energy range of $0–50\mathrm{eV}$. The subtle differences in electronic and optical properties can be attributed to the higher symmetry, coordination number of Ga atoms, and packing density in $\alpha \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ relative to that in $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$.

• Received 28 August 2006

DOI:https://doi.org/10.1103/PhysRevB.74.195123