Doping study of ultra-wide bandgap spinel semiconductor ZnGa₂O₄ films

ZnGa₂O₄ is a cubic spinel oxide with a bandgap of about 4.6 eV, almost same as that of monoclinic b-Ga₂O₃ in which the interest keeps increasing for its potential in high power devices. We will report the effect of various dopants on ZnGa₂O₄. For this study, we grew ZnGa₂O₄ films on c-Al₂O₃ substrates via pulsed laser deposition. XRD analysis confirmed the epitaxial growth of the films. Three elements, Sn, Si, and H were chosen as dopant candidates. The Sn-doped film remained highly insulating, showing no significant decrease in resistivity compared to the undoped film. The resistivity of the Si-doped film decreased to the order of 10³ Ω*cm, confirming that some carriers were generated by Si dopants. The H-doped films showed a large decrease in resistivity down to the order of 10^-1 Ω*cm. Further annealing of the H-doped films under an O₂ environment increased the resistivity up to the order of 10⁰ Ω*cm while the Hall measurements on the post-annealed H-doped films yielded mobility values of up to ~50 cm²*V^-1*s^-1 with a carrier density of ~10¹⁷ cm^-3.