Impact Ionization Generation occurs when, for example, an energetic electron undergoes a collision in which it loses sufficient energy to promote an electron in the valence band to the conduction band, resulting in an additional electron hole pair being produced. It is the mechanism responsible for avalanche breakdown. Select this option from the Generation–Recombination submenu.

The values of αn and αp can be user defined or can be related to the material properties in the following manner:

where E||,n and E||,p are the components of the electric field parallel to the electron and hole currents respectively and Tref, an, ap, bn, bp, cn, cp, dn, and dp are material properties.

If the check box is selected, then additional degrees of freedom are created for the generation rate. This allows the use of the Previous Solution node in the solver sequence to delay the update of the generation rate, which helps convergence at the expense of the accuracy of the solution (take smaller steps to check the accuracy).

The default Impact Ionization model is Okuto–Crowell model. For User defined, enter a desired value or expression in the input field for the values of αn and αp.

For the Okuto–Crowell model, the default Temperature reference Tref is 300 K. Two Okuto–Crowell ionization parameters n0 and m0 are set to 1 and 2, respectively, as default values. Change these values to adapt to a different model, for example, n0 = 0 and m0 = 1.

For the Okuto–Crowell model, the defaults for the following are all taken From material. For User defined, enter a different value or expression in the text field.