Current gain and transit-time effects in HBTs with graded emitter and base regions

Author

Zhang, Q.M. ; Tan, G.L. ; Xu, Jing Ming ; Day, D.J.

Author_Institution

Dept. of Electr. Eng., Toronto Univ., Ont., Canada

Volume

11

Issue

11

fYear

1990

Firstpage

508

Lastpage

510

Abstract

Two-dimensional simulations of the combined effects of emitter and base grading on the current gain and cutoff frequency f/sub t/ of heterojunction bipolar transistor (HBT) devices are presented. At low bias, the highest current gain was found to be obtained with an abrupt emitter and reduced by base grading, with f/sub t/ proportional to the collector current. At high bias, current gain was found to be enhanced by emitter grading, while base grading was found to reduce current gain if without emitter grading. Anticipated grading effects of lower band spikes and base transit time are found to be greatly modified by the changes of carrier density, lifetime, diffusion potential, and series resistance with bandgap.<>

Keywords

heterojunction bipolar transistors; semiconductor device models; 2D simulations; HBT; abrupt emitter; bandgap; base transit time; carrier density; carrier diffusion; carrier lifetime; collector current; current gain; cutoff frequency; diffusion potential; graded base regions; graded emitter; heterojunction bipolar transistor; high bias; low bias; lower band spikes; series resistance; transit-time effects; Analytical models; Bipolar transistors; Charge carrier density; Cutoff frequency; Heterojunction bipolar transistors; Numerical simulation; Photonic band gap; Radiative recombination; Semiconductor devices; Smoothing methods;

fLanguage

English

Journal_Title

Electron Device Letters, IEEE

Publisher

ieee

ISSN

0741-3106

Type

jour

DOI

10.1109/55.63015

Filename

63015