High-performance HfO2 dielectric gated Ge-doped <b> <i>κ</i> </b> -Ga2O3 thin-film transistors

Orthorhombic κ-Ga2O3 has emerged as a promising candidate for next-generation power electronics due to its ultra-wide bandgap and high breakdown field. Herein, Ge-doped Ga2O3 thin films were grown via pulsed laser deposition as active channels on c-sapphire, 6° off-axis c-sapphire (6°/c-sapphire), and MgO (100) substrates to explore thin-film transistors (TFTs). Ge was strategically introduced to stabilize the κ-phase and control carrier concentrations in the range of 1016–1017 cm−3. Top-gate TFTs were fabricated utilizing HfO2 as the high-k gate dielectric and Ti/Au as source/drain Ohmic contacts. Structural analyses indicate that substrate choice is critical: MgO(100) favors β−Ga2O3, while sapphire promotes κ-Ga2O3. Notably, the 6°/c-sapphire substrates yielded smooth films with minimal defects, which achieved an optimal carrier concentration (3.98 × 1017 cm−3) and a peak Hall mobility of 3.95 cm2 V−1 s−1. Corresponding TFTs exhibited superior enhancement-mode characteristics with a threshold voltage of 2.6 V, subthreshold swing of 1.48 V/dec, and a high current on/off ratio of 7.16 × 105. Technology-computer-aided-design simulations suggest a theoretical breakdown voltage of 298 V, limited primarily by gate-edge field crowding. This work demonstrates that synergistic strategy of Ge doping and 6°/c-sapphire substrate use can lead to high-quality κ-phase Ga2O3:Ge for high-performance power electronics.