Orientation dependent complex bandstructure of Si1−xGex alloys

Over the last decade, Si_1-xGe_x has increasingly been used as a channel material in MOSFETs. Though many studies have dealt with the real bandstructure of Si_1-xGe_x, the effect of germanium mole fraction x on complex bandstructure has been unexplored. Complex bands fundamentally determine band to band tunneling (BTBT) current. For example, using the orientation dependent complex bandstructure of silicon, it has been shown that the BTBT current in the [110] direction is an order of magnitude larger than that along the [100] direction. BTBT contributes significantly to off-current I_off in conventional MOSFETs, via the mechanism of gate induced drain leakage (GIDL). Additionally, BTBT determines the on current I_on in tunneling FETs, which have been suggested as next generation devices. Further, BTBT is more dominant in Si_1-xGe_x than silicon, owing to a narrower bandgap. In this work, we determine the orientation dependent complex bandstructure of Si_1-xGe_x along common crystallographic directions and predict trends in BTBT current.