Bandgap engineering in vertical P-MOSFETs

Bandgap engineering in vertical P-MOSFETs has been investigated in view of suppressing the short channel effects, floating body effect, and improving the drive current. SiGe source heterojunction P-MOSFETs have been used to suppress the short channel effects for sub-100 nm devices. While the leakage is reduced, the drive current is also reduced due to the use of a heterojunction. In this paper, we discuss a SiGe source heterojunction vertical P-MOSFET with a few nanometers thick Si cap. With this device structure, the absence of the heterojunction-induced potential barrier right below the oxide interface improves the drive current substantially while the drain induced barrier lowering effect and floating body effect are still suppressed. To further improve the drive current of the device, a SiGe/Si cap was added to the SiGe heterojunction P-MOSFET. We call this device a high mobility heterojunction MOSFET (HMHJT). Compared with the Si control device, the HMHJT has higher drive current and less off-state current at the same time.