An analytical model for the low- emitter-impurity-concentration transistor

The epitaxial transistor model developed by Grung and Warner is adapted for predicting the characteristics of the low-emitter-impurity-concentration (LEC) transistor. The model predicts the following results for the low region (the lightly-doped emitter region): through a given cross section, the minority-carrier drift current is typically larger than the minority-carrier diffusion current. In other words, the model predicts that the conventional low-level minority-carrier diffusion equation is invalid for the low region, especially for typical bias levels. As a result, the effect of the electric field on minority carriers cannot be neglected in the low region of the LEC transistor and (by extension) in the corresponding low regions of such devices as the epitaxial diode and the integrated-injection-logic transistor.