Base-transit-time model considering field dependent mobility for BJTs operating at high-level injection

• Published in: IEEE transactions on electron devices Vol. 53; no. 10; pp. 2532 - 2539
• Main Authors: Hassan, M.M.S., Nomani, Md.W.K.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-10-2006; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Base transit time; bipolar junction transistors (BJTs); Bipolar transistors; Charge carrier density; Charge carrier mobility; Computer simulation; Devices; Diffusion processes; Electronics; Exact sciences and technology; high injection; Junction transistors; Mathematical analysis; Mathematical models; Saturation; Semiconductor device doping; Semiconductor device modeling; Semiconductor devices; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Transistors; Transit time; Transit time; Doping; Doped materials; high injection; Bipolar transistor; bipolar junction transistors (BJTs); Junction transistors; Analytical method; Numerical simulation; Electron density; Base transit time; Base collector junction; Charge carrier injection; Kirk effect
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2006.882269

An analytical model for the base transit time tau b for an exponentially doped base is developed assuming a small change in electron concentration in the base of a bipolar junction transistor at high injection from its low injection value. The model is valid in all levels of injection before the onset of the Kirk effect. In this analysis, bandgap-narrowing effect, high-injection effect, and carrier velocity saturation at the base edge of the base-collector junction, and also doping and field dependence of mobility, are incorporated. The base transit time calculated analytically is compared with simulation and numerical results, and also with experimental data in order to demonstrate the validity of the assumptions made in deriving the expression. The base transit time is found to be different if the field dependent mobility is considered