Device Design of High–Speed Source–Heterojunction–MOS Transistors (SHOTs): Optimization of Source Band Offset and Graded Heterojunction

We have studied the device design of 15-nm highspeed n-channel source-heterojunction-MOS transistors (SHOTs) utilizing high-velocity electron injection from the source into the channel region and using the conduction-band-offset energy between the source and the channel regions. The band-offset energy near the source region and the length of the graded heterojunction are key parameters for realizing high-speed operation of SHOTs. A 2D device simulator indicates that the enhancement in transconductance G_m in SHOTs on an SOI substrate over conventional SOI-MOSFETs without source-heterojunction structures strongly depends on the source conduction-band-offset value DeltaE_c and the length of graded-heterojunction structures L_H in SHOTs. Moreover, the G_m enhancement of SHOTs is affected by the drain and the gate biases. We have shown that, with fully optimized DeltaE_c and L_H values, the G_m enhancement of SHOT due to high-velocity electron injection can be achieved in a whole range of drain bias. The optimized SHOT is quite promising for high-speed CMOS devices in the 10-nm regime.