Profile design considerations for minimizing base transit time in SiGe HBTs for all levels of injection before onset of Kirk effect

• Published in: IEEE transactions on electron devices Vol. 48; no. 8; pp. 1540 - 1549
• Main Authors: Kwok, K.H., Selvakumar, C.R.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2001; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Diffusion coefficient; Doping; Germanium; Germanium alloys; Mathematical analysis; Optimization; Silicon germanides; Simulation; Transit time
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/16.936506

An iteration scheme to calculate the base transit time (/spl tau//sub b/) for a given collector current density is developed in order to determine the optimal doping profile and Ge profile in the neutral base for minimizing the /spl tau//sub b/ of SiGe HBTs under all levels of injection before the onset of the Kirk effect. We adopt a consistent set of SiGe transport parameters, tuned to measurement data, and include important effects such as the electric-field dependency of the diffusion coefficient and plasma-induced bandgap narrowing in our study. The scheme has been verified with simulation results reported in the literature. Our study shows that under both low and high injection, for a given Ge dose, intrinsic base resistance, and base concentration near the emitter, a retrograde doping profile with a trapezoidal Ge profile gives the minimum /spl tau//sub b/.