ULTRAFAST PHOTODETECTION WITH AN ALINAS GAINAS HETEROJUNCTION BIPOLAR-TRANSISTOR/

Femtosecond visible-wavelength optical pulses were injected into unmod ified AlInAs/GaInAs single-heterojunction bipolar transistors with cur rent unity-gain frequencies of approximately 20 GHz. Emitter photocurr ent transients as fast as 2.4 ps, corresponding to a photodetection ba ndwidth in excess of 200 GHz, were measured electro-optically. The res ponsivity was as high as 0.078 A/W at 620 nm. Slow photocurrent compon ents due to photogenerated holes could be canceled with appropriate ba se biasing; measurements of the slow photocurrents provided informatio n about the dynamics of carrier recombination in the base.