Cryogenic temperature performance of modulation-doped field-effect transistors

We report S-parameter measurements of AlInAs/GalnAs/ InP modulation-doped field-effect transistors (MODFETs) at cryogenic temperatures. The current gain at 80 K is 3dB higher than at 300 K, and the current gain cutoff frequency fT increases from 32 GHz at 300 K, to 42 GHz at 80 K, which is the first observation of higher fT by direct measurement.