With channel length scaling into tens of nanometers at the current 45 nm technology node and beyond, the carrier transport is becoming more and more ballistic which is analogous to throwing a ball in the air, i.e. traveling without scattering. In ballistic transport, the concept of mobility does not exist and the drive current is rather controlled by the carrier injection velocity which is a material property. The injection velocity, however, can be improved by providing excess kinetic energy to the carriers through band bending, for example utilising a heterogeneous source to channel junction.

IME researchers have fabricated a high-carrier injection velocity Ge-rich Silicon-Germanium (SiGe) nanowire MOSFET in nearly gate-all-around architecture. The hetero-junction nanowire (source/drain with 30%Ge and nanowire channel with ~70% Ge) fabricated using pattern dependent Ge condensation method is integrated into a PMOSFET with HfO2 as high-K gate dielectric along with Tantalum Nitride metal gate. The fabricated hetero-junction device with nanowire of diameter ~13 nm exhibits significant drive current improvement (~4.5x) compared to the corresponding planar device. Along with enhanced hole injection velocity caused by hetero-junction between source and channel, compressive strain and high Ge contents in the nanowire are speculated as possible causes of the improvement.

Figure: (a) Nanowire device after gate patterning (top) with TEM cross-section image of the nanowire channel. (b) Transconductance, gm, plot (top) and out-put characteristics (bottom) comparing the nanowire device performance with planar reference device.