Injection-induced bandgap narrowing and its effects on the low-temperature operation of silicon bipolar transistors

Abstract

The authors present evidence that injection-induced bandgap narrowing plays an important role in determining the low-temperature properties of silicon bipolar transistors. This phenomenon occurs when large concentrations of minority-carrier charge are injected into the quasi-neutral base region of the device under high-current conditions. A significant enhancement in the low-temperature transistor current gain in the high-current regime is produced that is unaccounted for in conventional device theory. Comparison of theoretical calculations as well as phenomenological modeling results to measured data supports the authors' claims. The analysis suggests that an understanding of injection-induced bandgap narrowing is required for accurate modeling of bipolar transistors, particularly when they are used in low-temperature applications.