A Fast and Accurate Method to Study the Impact of Interface Traps on Germanium MOS Performance

Abstract

A technique is presented to study the electrostatic degradation of key germanium metal-oxide-semiconductor field-effect transistor (MOSFET) performance metrics such as the subthreshold slope SS, the drive current, and the off-state current. This is calculated using the superposition of the contributions from individual trap profiles, arising from a piecewise approximation of any arbitrary interface-trap spectrum. A technology computer-aided design simulation using this approach has been directly applied to the electrical evaluation of various scaled Ge p-channel FETs with different passivation schemes. The relative SS degradation due to interface traps is shown to be independent of the gate length, even in scaled devices exhibiting short-channel effects. Additionally, a linear dependence of the relative degradation with an equivalent oxide thickness (EOT) is observed. As such, a transistor's subthreshold performance is less impacted by a given concentration of interface traps, as the EOT is further reduced. Finally, the MOSFET drive current is shown to be degraded due to interface traps, mainly through additional scattering in the channel, while the electrostatic effect is rather small.