Physics of enhanced impact ionization in strained-Si p-channel metal-oxide-semiconductor field-effect transistors

This paper investigates the impact ionization phenomenon in strained-Si p-channel metal-oxide-semiconductor field-effect transistors with different strained-Si cap layer thicknesses at a Ge content of 20%. From the relationship between the impact ionization efficiency and the electric field in the pinch-off region, the strain-induced enhancement of the impact ionization efficiency appears to be quite consistent despite the high hole mobility and considerable scattering in the strained-Si cap layer; this consistent enhancement can be attributed to a decrease in the bandgap energy, regardless of the modification of the mean free path of the holes.