Monte Carlo study of sub-band-gap impact ionization in small silicon field-effect transistors

The observation of impact ionization in small Si FETs at sub-band-gap source-to-drain bias is explained by the presence of high-energy tails in the electron energy distribution around the drain region. These tails are caused by the strong thermalizing effect of dynamically-screened electron-electron interactions. Under these bias conditions, a larger band-gap, enhanced dielectric screening, and reduced high-energy tails in the distribution function at the source cause a reduction of impact ionization at lower lattice temperatures.