  High frequency operation of tunneling real-space transfer transistor (TRSTT)
in the negative differential resistance (NDR) regime is assessed by calculating
the device common source unity current gain frequency (fT) range with a small
signal equivalent circuit model including tunneling. Our circuit model is based
on an In0.2Ga0.8As and delta-doped GaAs dual channel structure with various
gate lengths. The calculated TRSTT fT agrees very well with experimental data,
limiting factor being the resistance of the delta-doped GaAs layer. By
optimizing the gate dimensions and channel materials, we find fT in the NDR
region approaches terahertz range, which anticipates potential use of TRSTT as
terahertz sources.
