High frequency study of nonequilibrium transport in heterostructure bipolar transistors.

We report results of studying non-equilibrium transport in heterostructure bipolar transistors at millimeter-wave band. Increasing the total potential drop in the collector from 0. 88 eV to 1.6 eV changes the measured intrinsic transit delay from 0.32 ps to 0.63 ps due to the increasing importance of intervalley scattering. Both the experimental and calculated data illustrate the role nonequilibrium transport and inter- valley scattering has in determining the fundamental limits to device performance.