Non-local impact ionization in silicon devices

In small bipolar and MOS transistors, the electrons gain much less energy than according to the maximum electric field. This is due to nonlocal electron heating and the small width of the E-field peak. The simplified energy balance equation with the energy relaxation length lambda /sub e/ as parameter gives the electron temperature for a given electric field distribution. From a series of MBE (molecular beam epitaxy)-grown bipolar transistors and scaled submicron MOS transistors, lambda /sub e/=650 AA was found. With the calculated temperature distribution and known empirical models for the impact ionization, avalanche (substrate) currents are accurately predicted. This procedure can easily be implemented, as postprocessing, in existing device simulators with hardly any extra computation time. It extends in a consistent way the validity range of these simulators to future device generations.<>