Self-aligned high-frequency InP/InGaAs double heterojunction bipolar transistors (DHBT's) have been fabricated on a Si substrate for the first time. A current gain of 40 was obtained for a DHBT with an emitter dimension of 1.6 × 19 μm2. The S parameters were measured for various bias points. In the case of Ic= 15 mA, fTwas 59 GHz at VCE= 1.8 V, and fmax was 69 GHz at VCE = 2.3 V. Due to the InP collector, breakdown voltage was so high that a high VCEof 3.8 V was applied for Ic = 7.5 mA in the S-parameter measurements to give an fTof 39 GHz and an fmax of 52 GHz.
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