Investigation of impact ionization using the balance-equation approach for multivalley nonparabolic semiconductors

We study the effect of impact ionization (II) on high-field electron transport in bulk Si with a conduction band composed of ellipsoidal X and L valleys, using the nonparabolic multivalley balance-equation method. The impact ionization process is described by the II-induced effective acceleration A(ii), the II-induced energy-loss rate W-ii, and the II rate g(ii), which are determined self-consistently during the process of the calculation. The calculated results such as average carrier velocity and the II coefficient show good agreement with experimental data and with MC simulation, thus confirming the validity of the model. An empirical relation of the field-and lattice temperature-dependence of the II coefficient is suggested, which may be useful in device simulation with the balance-equation theory. (C) 1998 Elsevier Science Ltd. All rights reserved.