Bandgap engineering of Si_1-xGe_x epitaxial tunnel layer for tunnel FETs

The effects of the Si_1-xGe_x epitaxial tunnel layer (ETL) scheme and ETL thickness on the ON-state current (ION) of Si_1-xGe_x ETL tunnel field-effect transistors (TFETs) are thoroughly studied in this work. Compared with using pure Ge as the ETL, implementing Si_1-xGe_x with linearly changing Ge content degrades ION markedly, whereas using Si_1-xGe_x with stepwise changing Ge content degrades ION slightly. Although changing the ETL material from Ge to Si_1-xGe_x leads to ION reduction, for practical implementation, it is anticipated that a better subthreshold swing (SS) can be obtained by ETL crystal quality improvement. The best Si_1-xGe_x ETL scheme for application in complementary Si_1-xGe_x ETL TFETs is 4-nm-thick Si_1-xGe_x with stepwise decreasing bandgap (E_g). It is believed that this structure is more promising for implementation.