Study of Random Dopant Fluctuation Effects in Germanium-Source Tunnel FETs

The effects of random dopant fluctuations (RDFs) on the performance of Germanium-source tunnel field-effect transistors (TFETs) is studied using 3-D device simulation. The RDF in the source region is found to have the most impact on threshold voltage variation (σ
V
_TH
) if the source is moderately doped (10
¹⁹
cm
^-3
) such that vertical tunneling within the source is dominant. If the source is heavily doped (10
²⁰
cm
^-3
) such that lateral tunneling from the source to the channel is dominant, the impact of RDF in the channel region is also significant. RDF-induced threshold voltage variation (σ
V
_TH
) for an optimally designed Ge-source TFET is relatively modest (σ
V
_TH
<; 20 mV at
Lg
= 30 nm), compared with a MOSFET of similar gate length. Supply voltage scaling is not beneficial for reducing TFET σ
V
_TH
.