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.