p-Type Ultrawide-Band-Gap Spinel ZnGa 2 O 4 : New Perspectives for Energy Electronics

The family of spinel compounds is a large and important class of multifunctional materials of general formulation AB 2 X 4 with many advanced applications in energy and optoelectronic areas such as fuel cells, batteries, catalysis, photonics, spintronics, and thermoelectricity. In this work, it is demonstrated that the ternary ultrawide-band-gap (∼5 eV) spinel zinc gallate (ZnGa 2 O 4 ) arguably is the native p-type ternary oxide semiconductor with the largest E g value (in comparison with the recently discovered binary p-type monoclinic β-Ga 2 O 3 oxide). For nominally undoped ZnGa 2 O 4 the high-temperature Hall effect hole concentration was determined to be as large as p = 2 × 10 15 cm –3, while hole mobilities were found to be μ h = 7–10 cm 2 /(V s) (in the 680–850 K temperature range). An acceptor-like small Fermi level was further corroborated by X-ray spectroscopy and by density functional theory calculations. Our findings, as an important step toward p-type doping, opens up further perspectives for ultrawide-band-gap bipolar spinel electronics and further promotes ultrawide-band-gap ternary oxides such as ZnGa 2 O 4 to the forefront of the quest of the next generation of semiconductor materials for more efficient energy optoelectronics and power electronics.