The microwave operation and modulation (3GHz) of an InGaPGaAs heterojunction bipolar transistor (HBT) laser is reported. The HBT layer structure is in the form of an optical waveguide (with cleaved ends) that also includes an InGaAs recombination quantum well in the p-type base region to improve the recombination radiation properties. The shift in HBT laser operation from spontaneous to stimulated emission is manifest as a distinct change in the HBT current–voltage characteristics, specifically a decrease in the common-emitter current gain (βdc=ICIB) and the occurrence of even a more striking peak in the small signal (ac) gain βac=ΔICΔIB.

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