Gate-stack engineering for self-aligned Ge-gate/SiO2/SiGe-channel Insta-MOS devices

We reported a first-of-its-kind, self-aligned gate-stack heterostructure of Ge-nanoshpere-gate/SiO₂/SiGe-channel on Si in a single-step approach through selective oxidation of a SiGe nano-patterned pillar over a Si₃N₄ buffer layer on Si substrate. Good tunability on the Ge-nanoshpere size, SiO₂ thickness, and SiGe-shell thickness provides a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS) devices with size-tunable Ge gates, SiO₂ gate oxide, and SiGe channels. Detailed interfacial morphologies and structural properties between the Ge nanosphere/SiO₂ and SiO₂/SiGe-channel were examined using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Both Al/SiO₂/Ge-nanospheres and NiGe/SiO₂/SiGe MOS capacitors exhibit quite low interface trap densities of 3-5×10¹¹ cm^-2eV¹, which is beneficial for advanced Ge MOS applications.