The effects of the Si1-xGex epitaxial tunnel layer (ETL) scheme and ETL thickness on the ON-state current (ION) of Si1-xGex ETL tunnel field-effect transistors (TFETs) are thoroughly studied in this work. Compared with using pure Ge as the ETL, implementing Si1-xGex with linearly changing Ge content degrades ION markedly, whereas using Si1-xGex with stepwise changing Ge content degrades ION slightly. Although changing the ETL material from Ge to Si1-xGex 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 Si1-xGex ETL scheme for application in complementary Si1-xGex ETL TFETs is 4-nm-thick Si1-xGex with stepwise decreasing bandgap (Eg). It is believed that this structure is more promising for implementation.