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(Color online) (a) Schematic of a double-gate (DG) TFET Device with silicon-germanium (SiGe) source. (b) A zoomed-in view of the source end of the DG TFET showing the heterojunction. The edge of the top gate is the origin for the axes. is defined with respect to the gate edge. The dotted vertical line located at is the position where the source doping concentration is , and most of the tunneling occurs in the region where the doping concentration is between . (c) Simulated gate transfer characteristics of the DG TFET with SiGe source at various . The Ge content is 20%. Lower threshold voltage with higher on-state current is observed as increases from .
Extracted energy band diagram along the source to channel direction near the surface for (a) , (b) and , and (c) and . The application of the drain and gate biases modulates the tunneling barrier width from the off state to the on state. With of , is reduced. This will enhance the band-to-band tunneling (BTBT) rate and hence on-state current .
Plot of (a) off-state current , and (b) on-state current , as a function of . Generally, both and increase as the overlap of the heterojunction with the gate increases. Both minimum and maximum points occur at a certain value of . This could be explained by the variation in electric field and tunneling barrier width as changes.
(a) Extracted maximum electric field along the source to channel direction near the surface for , and , and and . The maximum electric field at various biases decreases as increases. (b) Extracted maximum BTBT tunneling rate along the source to channel direction near the surface for and .
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