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 (E_g), intrinsic carrier concentration (n_i), and permittivity (∈). 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.