A mechanism for impact ionization of Si n-channel MOSFETs

Abstract

Cross-gap excitation by the collision of a conduction electron and a valence electron in the drain junction of an Si n-channel MOSFET is discussed on the basis of substrate current characteristics and light emission spectra. The characteristic curve of the logarithm of substrate current relative to drain current vs drain voltage is represented by a "refracted" straight line. The refraction in the characteristic curve can be related to electron-hole pair creation by an indirect interband transition along the Δ-axis of the Brillouin zone. A broad peak is found around 2-2.5 eV in the light emission curve above the drain voltage of 5 V. This peak is due to radiative recombination along the Δ-axis, superimposed on a monotonic emission curve due to bremsstrahlung. The indirect interband transition along the Δ-axis plays a significant role in impact ionization in a high electric field. © 1992.