Reduction of f/sub t/ by nonuniform base bandgap narrowing
- 1 August 1989
- journal article
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Electron Device Letters
- Vol. 10 (8), 341-343
- https://doi.org/10.1109/55.31750
Abstract
Analytical and simulation results are presented to illustrate qualitatively the effect of doping on base transit time. Nonuniform base bandgap narrowing (BGN) in silicon bipolar transistors can give rise to an electric field that is comparable to and against the built-in field. The base transit time tau is subsequently increased, leading to a deterioration of the cutoff frequency f/sub 1/. It is shown that the BGN effectively reduces the impurity profile grading factor K and subsequently the transit-time coefficient eta . Physically, the minority carriers can be thought of as moving in a new profile characterized by a reduced eta but in the absence of BGN. Unlike earlier investigations which also consider effective BGN dopings but ignore the field effects, this treatment includes their impact on the minority-carrier base transit time. For a steep exponential profile with strong BGN, an increase of eta by a factor 3.57 at 300 K is calculated. Device simulations predict a smaller f/sub t/ reduction factor of 1.5 for more general profiles.Keywords
This publication has 5 references indexed in Scilit:
- A unified electrothermal hot-carrier transport model for silicon bipolar transistor simulationsSolid-State Electronics, 1989
- The importance of surface recombination and energy-bandgap arrowing in p-n-junction silicon solar cellsIEEE Transactions on Electron Devices, 1979
- Factors limiting current gain in power transistorsIEEE Transactions on Electron Devices, 1977
- Theoretical effects of surface diffused region lifetime models on silicon solar cellsSolid-State Electronics, 1977
- Measurements of bandgap narrowing in Si bipolar transistorsSolid-State Electronics, 1976