Bandgap engineering of Si1-xGex epitaxial tunnel layer for tunnel FETs

Abstract

The effects of the Si-1-xGe(x) epitaxial tunnel layer (ETL) scheme and ETL thickness on the ON-state current (l(ON)) of Si-1_Ge-x(x) 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 l(ON) markedly, whereas using Si1-xGex with stepwise changing Ge content degrades l(ON) slightly. Although changing the ETL material from Ge to Si1-xGex leads to l(ON) 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 (E-g).( )It is believed that this structure is more promising for implementation. (C) 2018 The Japan Society of Applied Physics.