Numerical simulation of hot-carrier transport in silicon bipolar transistors

Conventional numerical simulations of bipolar transistors assume that the carrier transport processes in the device can be described by the semiconductor equations with electric-field dependent mobility and the Einstein relation between the mobility and diffusion coefficient. These assumptions are not generally valid for the large electric fields, current densities, and concentration gradients present in advanced bipolar transistors. In this work, we present a new numerical bipolar device simulation which provides a better description of the carrier transport processes in these devices. Specifically, the carrier mobilities and diffusion coefficients are treated as functions of the average carrier energy and the thermoelectric current resulting from spatial variations in the carrier energies is included. The required carrier energies are calculated using energy balance equations. The results of this simulation are compared with those calculated using a conventional bipolar-device simulation, and the differences are discussed.