IGFET hot electron emission model

Hot electrons emitted from the semiconductor of an IGFET may provide a fundamental limit to IGFET technology. Threshold voltage shifts are observed on interchanging source and drain terminals of devices stressed at junction biases less than avalanche breakdown voltage. A two-dimensional phenomenological model was developed to predict emission levels of electric-field-activated hot electrons from the semiconductor surface of IGFETs. This model predicts reverse threshold voltage shifts using empirical curves for normalized threshold voltage shift as a function of emitted current for a given insulator. Calculated reverse threshold shifts agree with measurements. Calculations of hot electron emission from the IGFET semiconductor are, for the first time, based on a two-dimensional analysis of device electric field and current flow. The probability that channel electrons gain energy greater than the insulator barrier height depends on collision mean free paths, impact ionization threshold energy, and insulator barrier height, in addition to the electric field. Results are given for the emission current´s dependence on channel length, source and drain impurity profile, substrate doping level, and electrical bias. The calculations show where electrons originate in the semiconductor. The region along the semiconductor-insulator interface across which emitted current passes is within a few hundred angstroms of the drain metallurgical junction.