Band Engineering to Improve Average Subthreshold Swing by Suppressing Low Electric Field Band-to-Band Tunneling With Epitaxial Tunnel Layer Tunnel FET Structure

Tunnel field-effect transistor (FET) is a promising candidate in ultralow-power applications due to its distinct operation mechanism, namely band-to-band tunneling (BTBT). The integration of different low-bandgap materials is explored extensively to improve the ON-state BTBT current of the tunnel FETs. The epitaxial tunnel layer (ETL) tunnel FET integrated with the hetero-material system is a promising structure due to its process compatibility with CMOS technologies. In the scenario of n-channel operation, the concept of the suppression of the low electric field BTBT is proposed. The SiGe/Si hetero-material system is applied to the n-channel ETL tunnel FET to suppress the low electric field BTBT by the ETL band engineering. The optimized ETL tunnel FET exhibits a high ON-state BTBT current due to the low bandgap material in the ETL. The average SS behavior is also further improved by suppressing the low electric field BTBT. In this study, the design concept and the device parameters of the n-channel ETL tunnel FET are discussed in detail. The performances of the complementary ETL tunnel FETs using the SiGe/Si hetero-material system are also provided to enrich the value of the ETL tunnel FET in the circuit applications.