ELECTRICAL AND OPTICAL-RESPONSE OF A VERY HIGH-FREQUENCY ALGAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTOR/

The current gain cutoff frequency of very high frequency AlGaAs/GaAs h eterojunction bipolar transistors has been measured at 300 and at 20 K using the picosecond optoelectronic technique. These devices showed c utoff frequencies of 72 and 84 GHz at room temperature and at a fixtur e temperature of 20 K, respectively. Optical response measurements wer e also obtained at visible and infrared wavelengths. The visible optic al response shows a FWHM of 14 and 9.5 ps at 300 and 20 K, respectivel y. The infrared (lambda=850 nm) optical response, corresponding to dee per penetration, showed a FWHM significantly larger (>50 ps) than the visible optical response.