The effect of hot-electron injection energy (Ei) into the base on the high-frequency characteristics of In0.52(Ga1-xAlx)0.48As/InGaAs abrupt heterojunction bipolar transistors (HBT’s) is investigated by changing the composition of the emitter. It is found that there exists an optimum Ei at which a maximum current gain cutoff frequency (fT) is obtained. Analysis of hot-electron transport in the base and collector by Monte Carlo simulation is carried out to understand the above phenomenon. The collector transit time (t c) increases with Eibecause electrons with higher energy transfer from the T valley into the upper L and X valleys. At first, the base transit time (Tb) decreases with Eiat the low Ei region. However, rbdoes not decrease monotonically with Eifor high Ei, because of the large nonparabolicity in the energy-band structure of InGaAs. Consequently, there exists a minimum in the sum of Tband Tc’in other words a maximum fT, at an intermediate value of Ei.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Electrical and Electronic Engineering