Ultra-wide bandgap, conductive, high mobility, and high quality melt-grown bulk ZnGa2O4 single crystals.

Truly bulk ZnGa₂O₄ single crystals were obtained directly from the melt. High melting point of 1900 ± 20 °C and highly incongruent evaporation of the Zn- and Ga-containing species impose restrictions on growth conditions. The obtained crystals are characterized by a stoichiometric or near-stoichiometric composition with a normal spinel structure at room temperature and by a narrow full width at half maximum of the rocking curve of the 400 peak of (100)-oriented samples of 23 arcsec. ZnGa₂O₄ is a single crystalline spinel phase with the Ga/Zn atomic ratio up to about 2.17. Melt-grown ZnGa₂O₄ single crystals are thermally stable up to 1100 and 700 °C when subjected to annealing for 10 h in oxidizing and reducing atmospheres, respectively. The obtained ZnGa₂O₄ single crystals were either electrical insulators or n-type semiconductors/degenerate semiconductors depending on growth conditions and starting material composition. The as-grown semiconducting crystals had the resistivity, free electron concentration, and maximum Hall mobility of 0.002–0.1 Ωcm, 3 × 10¹⁸–9 × 10¹⁹ cm⁻³, and 107 cm² V⁻¹ s⁻¹, respectively. The semiconducting crystals could be switched into the electrically insulating state by annealing in the presence of oxygen at temperatures ≥700 °C for at least several hours. The optical absorption edge is steep and originates at 275 nm, followed by full transparency in the visible and near infrared spectral regions. The optical bandgap gathered from the absorption coefficient is direct with a value of about 4.6 eV, close to that of β-Ga₂O₃. Additionally, with a lattice constant of a = 8.3336 Å, ZnGa₂O₄ may serve as a good lattice-matched substrate for magnetic Fe-based spinel films. [ABSTRACT FROM AUTHOR]