Combined Effects of an Epitaxial Ge Channel and Si Substrate on Ge-on-Si Metal–Oxide–Semiconductor Capacitors and Field Effect Transistors

Electrical characteristics of metal–oxide–semiconductor (MOS) capacitors and transistors fabricated on Ge epitaxial layers exhibit a strong dependence on layer structures, such as the Ge epitaxial layer thickness, Si cap layer, and Ge channel doping. The dependence in Ge-on-Si devices is associated with different material parameters of epitaxial Ge layers and Si substrates, such as bandgap energy (Eg), intrinsic carrier concentration (ni), and permittivity (e). The flat band voltages of capacitors are independent of the thickness of epi-Ge layer grown on Si substrates. The threshold voltages, however, exhibit strong dependency on layer structures. Non-ideal capacitance–voltage characteristics, such as low frequency behavior and frequency dispersion, are also determined by combined effects of Ge-on-Si heterostructures.