Investigation of current transport and charges in graded base HBTs

Abstract
An all injection model for graded-base HBTs (heterojunction bipolar transistors) has been developed and found to agree well with experimental results. The model shows that assuming low injection level and base transit time current independence may not be valid in all cases. Recombination current components have been formulated. The base grading effect on current components and current gain is investigated. The results show that as Al mole fraction increases gain increases to a maximum, then decreases Author(s) Ryum, B.R. Dept. of Electr. Eng. & Comput. Sci., Northwestern Univ., Evanston, IL, USA Abdel-Motaleb, I.M.