Hetero-Tunnel Field-Effect-Transistors With Epitaxially Grown Germanium on Silicon

The epitaxially grown Ge (epi-Ge)/Si hetero-tunnel field-effect transistors (HTFETs) is demonstrated to enhance band-to-band tunneling (BTBT) current because of effective bandgap reduction. The epi-Ge HTFET has a drain current as high as 11 μA/μm at V_GS=V_DS=-2 V, which enhances 2.3× as compared with that of Si, and the drain-induced barrier thinning (DIBT) shows 28 mV/V. The smaller subthreshold swing of epi-Ge HTFET is obtained as compared with Si. The current mechanism of BTBT is confirmed at the interface of epi-Ge/Si hetero-tunneling occurring in the n⁺-region by hole barrier height extraction. The gate/source overlap lengths for parallel-plate tunneling region are discussed for current and DIBT.