High-frequency study of nonequilibrium transport in heterostructure bipolar transistors

We report results of studying nonequilibrium transport in heterostructure bipolar transistors at a millimeter-wave band. Increasing the total potential drop in the collector from 0.88 to 1.6 eV changes the measured intrinsic transit delay from 0.32 to 0.63 ps due to the increasing importance of intervalley scattering. Both the experimental and calculated data illustrate the role nonequilibrium transport and intervalley scattering have in determining the fundamental limits to device performance.