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-TiO2 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/Al2O3/Ge capacitors with different Al2O3 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.