ULTRAFAST PHOTODETECTION WITH AN ALINAS/GAINAS HETEROJUNCTION BIPOLAR-TRANSISTOR

Femtosecond visible-wavelength optical pulses were injected into unmodified AlInAs/GaInAs single-heterojunction bipolar transistors with current unity-gain frequencies of approximately 20 GHz. Emitter photocurrent transients as fast as 2.4 ps, corresponding to a photodetection bandwidth in excess of 200 GHz, were measured electro-optically. The responsivity was as high as 0.078 A/W at 620 nm. Slow photocurrent components due to photogenerated holes could be canceled with appropriate base biasing; measurements of the slow photocurrents provided information about the dynamics of carrier recombination in the base.