Bilayer metal oxide gate insulators for scaled Ge-channel metal-oxide-semiconductor devices

We investigate the electrical properties of germanium-channel metal-oxide-semiconductor capacitors with an amorphous atomic-layer-deposited (ALD)-Al₂O₃ interlayer (IL) and higher- k ALD-TiO ₂ gate dielectric. An ALD-Al₂O₃ IL of ∼1 nm thickness reduces the gate leakage current density at the otherwise low band-offset TiO₂ /Ge interface by six orders of magnitude at flatband. Devices with the thinnest Al₂O₃ IL exhibited a low capacitance equivalent thickness of 1.2 nm. The hysteresis of the capacitance-voltage curves was <10 mV for TiO₂/Al ₂O₃/Ge capacitors with different Al₂O ₃ thicknesses. We obtained a relatively low minimum density of interface states, Dit ∼3× 10¹¹ cm^-2 eV ^-1, suggesting the potential of Al₂O₃ ILs for higher- k/Ge interface passivation.