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 ( ε ). 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.