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<i>V</i><sub>TH</sub>) if the source is moderately doped (10<sup>19</sup> cm<sup>-3</sup>) such that vertical tunneling within the source is dominant. If the source is heavily doped (10<sup>20</sup> cm<sup>-3</sup>) 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<i>V</i><sub>TH</sub>) for an optimally designed Ge-source TFET is relatively modest (σ<i>V</i><sub>TH</sub> <; 20 mV at <i>Lg</i> = 30 nm), compared with a MOSFET of similar gate length. Supply voltage scaling is not beneficial for reducing TFET σ<i>V</i><sub>TH</sub>.

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