High-Performance Composite-Collector InP/InGaAs Heterojunction Bipolar Transistors

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This paper describes composite-collector InP/InGaAs heterojunction bipolar transistors that exhibit high current density and good breakdown behavior simultaneously. The collector consists of 150-nm InGaAs and 150-nm lightly $n$-type doped InP. Additionally, a 30-nm-thick InGaAsP layer is sandwiched between them to minimize the accumulation of transit carriers. The proposed structure makes use of the space charge in the collector to reduce the collector-current multiplication coefficient. At high current density, the space charge decreases the electric-field intensity in the narrow-band-gap InGaAs and moves the high-electric-field region into the wide-band-gap InP. The fabricated transistors exhibit flat collector $I$-$V$ curves, high current density of over 4 mA/μm2, and reasonably small knee voltage. They also show a peak $f_{\text{t}}$ of over 200 GHz and a peak $f_{\text{max}}$ of about 350 GHz at a current density of 2 mA/μm2. The ring oscillator IC based on the emitter-coupled-logic gate provides the gate propagation delay of 3.83 ps/stage.
2004-04-15