Demonstration of enhancement-mode high-k gated field-effect transistors with a novel ultrawide bandgap semiconductor: Germanium oxide

Ultrawide-bandgap (UWBG) semiconductors have been extensively investigated due to their potential applications in power devices and solar-blind detectors. Recently, germanium oxide (GeO₂) has been considered as a novel UWBG semiconductor due to its superior properties compared to the famous UWBG gallium oxide (Ga₂O₃), including ambipolar dopability, higher thermal conductivity, and higher carrier mobility. At present, most works about GeO₂ are still limited to theoretical studies and material characterizations, to some extent lacking demonstrations of field-effect transistors (FETs) with GeO₂ channels. In this work, GeO₂ FETs were successfully fabricated on SiO₂ gate dielectric via room-temperature sputtering. The as-deposited pristine GeO₂ film shows an insulator-like behavior, which can be converted to semiconductor-like by handily co-sputtering Sn as dopants. Correspondingly, GeO₂ FETs with depletion mode are obtained to present a high breakdown voltage of 260 V, which is superior for a planar 28.5-nm thin GeO₂ film without structure design. Moreover, a high thermal conductivity of 26.6 W m⁻¹ K⁻¹ is obtained for GeO₂ FETs at 300 K, which is around twice as high as that of Ga₂O₃. Furthermore, high-k HfLaO that was annealed in oxygen was adopted to replace the traditional SiO₂ gate dielectric to convert the depletion mode to enhancement mode, which is preferable for power devices due to energy efficiency. Finally, a high current density of 0.3 mA/mm and a low threshold voltage of 5.0 V are obtained for the high-k gated GeO₂ FET, which verifies the feasibility of using UWBG GeO₂ in FET devices to encourage further explorations on this novel UWBG semiconductor.