By using an energy transport model, we simulate cutoff frequency fT- versus collector current density Ic characteristics of npn-n AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with various n--collector thickness and n--doping densities. It is found that the calculated fr characteristics show double peak behavior when the n--layer is thick enough and the n--doping is high enough to allow existence of neutral n--region. The mechanism of the double peak behavior is discussed by studying energy band diagrams, electron-energy profiles and electron-velocity profiles. Particularly, we discuss the origin of the second peak (at higher Ic) which is not usually reported experimentally.
ASJC Scopus subject areas
- コンピュータ グラフィックスおよびコンピュータ支援設計