Strained-Si single-gate versus unstrained-Si double-gate MOSFETs

Self-consistent full-band Monte Carlo simulations are employed to compare the performance of nanoscale strained-Si single-gate (SG) and unstrained-Si double-gate (DG) MOSFETs for a gate length of 25 nm. Almost the same on-current as in the DG-MOSFET can be achieved by strain in a SG-MOSFET for the same gate overdrive. This is due to the compensation of the higher electron sheet density in the two inversion channels of the DG-MOSFET by the higher strain-enhanced velocity in the channel of the SG-MOSFET. The on-current of the strained-Si SG-MOSFET is almost 10% larger for a channel orientation along the crystallographic 〈100〉 direction than for the 〈110〉 direction. This confirms that the on-current is determined by quasi-ballistic transport, because the maximum enhancement of the in-plane velocity in bulk (001)-strained Si in the 〈100〉 direction is 5% at medium electric fields (the low-field mobilities and saturation velocities are the same and the difference in the thermal injection velocities is negligibly small), whereas the transient bulk velocity overshoot peak is 30% larger in the 〈100〉 direction.