Heterojunction Tunneling Transistors Using Gate-Controlled Tunneling Across Silicon–Germanium/Silicon Epitaxial Thin Films

摘要

Tunneling transistors that incorporate in the gated source an elevated $ hbox{p}^{+} hbox{Si}_{0.6}hbox{Ge}_{0.4}/hbox{n}^{-}$ Si heterojunction and a $hbox{HfO}_{2}$/WN gate stack are constructed. XTEM images show intact epitaxial SiGe with sub-10-nm thickness. The current/voltage characteristics within 77 K–300 K show behavior consistent with gate-controlled tunneling over several decades of current. Simulations using a nonlocal tunneling model support a tunneling process that occurs across the heterojunction. There is sufficient gate modulation of the surface potential at the $hbox{p}^{+}$ SiGe/gate-insulator interface to provide the band overlap and band bending for band-to-band tunneling (BTBT). The transfer and output characteristics are considerably improved over previous devices that used buried SiGe films, ion-implanted junctions, and $hbox{SiO}_{2}$ dielectrics, resulting in a reduced minimum subthreshold slope and an increased current drive with identical biasing. Also, due to the asymmetry in this structure and suppression of drain BTBT, $I_{rm on}/I_{ rm off} > hbox{10}^{5}$ is achieved with $V_{rm dd} = hbox{2.5 V}$.