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

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.