Subnanometer-equivalent-oxide-thickness germanium p-metal-oxide-semiconductor field effect transistors fabricated using molecular-beam-deposited high-k/metal gate stack

Metal-oxide-semiconductor field effect transistors (MOSFET) with a thin high-$k$ dielectric were fabricated on bulk $n$ -type germanium substrates. Surface oxides were thermally desorbed in situ by heating the substrates under ultrahigh vacuum conditions. First an ultrathin passivating layer was formed by evaporating germanium in the presence of atomic oxygen and nitrogen supplied from a remote radio frequency plasma source. Subsequently, the ${\mathrm{HfO}}_2$ dielectric was deposited by evaporating hafnium in the presence of atomic oxygen. An in situ $\mathrm{TaN}$ metal gate was similarly deposited. Long channel devices were fabricated using a standard process flow. These devices exhibited a low equivalent oxide thickness (EOT) of $0.7\mathrm{nm}$ with gate leakage less than $15\mathrm{mA}∕{\mathrm{cm}}^2$ at $V_{\mathrm{FB}}+1\mathrm{V}$ . Device mobility was extracted from $I_s\text{-}{V}_g$ and split $C\text{-}V$ characteristics. Results indicate a $2\times$ mobility enhancement in Ge $p$ -MOSFET devices compared to Si control devices. The demonstration of subnanometer EOT suggests that high-$k$ gate dielectrics on germanium are scalable to low EOT and suitable for use in ultrascaled MOSFET devices.