Single crystal growth and electrical properties modulation of ZnGa2O4

Abstract

ZnGa₂O₄ crystal is a type of ultra-wide bandgap semiconductor material known for their high electrical conductivity, ease of doping, and high symmetry, is ideal candidate material for applications in power electronics and optoelectronics. However, the lack of large size and high-quality ZnGa₂O₄ crystals has hindered its further development. Here, the vertical gradient freeze (VGF) method has been employed to successfully grow large-size bulk ZnGa₂O₄ single crystals of approximately 40 cm³ from the melt. The obtained ZnGa₂O₄ single crystals have an optical band gap of about 4.59 eV, a sharp absorption edge at about 280 nm, and great transparency in the UV spectrum. The ZnGa₂O₄ samples have the FWHM of the rocking curve of (111)-oriented of about 36 arcsec. A series of ZnGa₂O₄ samples with varying initial compositions of zinc oxide have been successfully grown. The electrical properties of the crystals were affected by varying excesses of zinc oxide in the initial components. By modulating the initial ZnO/Ga₂O₃ ratio, we reveal a defect engineering strategy to tailor electrical properties, enabled by suppressing Ga_Zn defects. As the excess of zinc oxide in the starting component increases, the crystal color becomes lighter and the electrical conductivity decreases. Among them, the highest electron concentration can reach 2.5 × 10¹⁹ cm⁻³, and the electron mobility reaches 55 cm² V⁻¹ s⁻¹, which is twice the mobility of gallium oxide at the same electron concentration. The isotropic thermal conductivity (22.8 W/(m*K)) further positions ZnGa₂O₄ as a superior candidate for high-power devices. Our work evaluates the potential of ZnGa₂O₄ for high-tech applications and provides direction for future research endeavors, offering a strategy to grow and modulate the electrical properties of bulk ZnGa₂O₄ crystals.