AlGaAs/GaAs P-n-p HBTs with high maximum frequency of oscillation

An investigation of P-n-p HBTs (heterojunction bipolar transistors) with an f/sub max/ of 39 GHz and an f/sub t/ of 19 GHz is presented. Power-added efficiency of 31% was obtained in an amplifier at 10 GHz. The design of the high-speed AlGaAs/GaAs P-n-p HBTs takes account of the large degeneracy in the heavily n-type GaAs base. This doping-dependent degeneracy can induce gradients in the valence-band edge to improve the base transit time. High injection efficiency can be maintained in spite of the large degeneracy by increasing the aluminum content of the emitter. HBTs with emitter aluminum contents of 40% and 75% are described.<
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