Two-stream instability and oscillatory regimes induced in ballistic diodesand field-effect transistors

Two groups of current carriers naturally coexist in ballistic and quasiball istic diodes and field-effect transistors (FETs): (1) traversing ballistic current carriers emitted by a source and absorbed by a drain, and (2) nontr aversing (nonparticipating in a current flow) carriers that: are in equilib rium with the drain carrier reservoir. Therefore, the convective two-stream instability develops in such diodes and FETs with appropriate physical and geometrical parameters. It can result in oscillatory regimes. In this arti cle, we consider development of the two-stream instability in n(+)nn(+) dio des with a doped bulk n-base, n(+)nn(+) diodes with a modulation doped n-ch annel base, and also in diodes with a gated n-channel base (that is in ball istic FETs) where a gate potential controls electron concentration in the c hannel. Since oscillatory regimes in such devices are restricted by pair el ectron-electron interaction between electrons belonging to the two differen t streams and participating in the instability process, we suggest a new ty pe FET with two parallel n channels. Current-carrying electrons from the pr imary channel interact with slow electrons from the parallel additional cha nnel that simultaneously serves as a controlling gate for the primary chann el. In this design, electron streams participating in the two-stream instab ility are spatially separated, and their pair interaction is suppressed. Al ong with analytic estimates, we present results of numerical simulations fo r the ballistic FETs that prove the existence of oscillatory regimes in ter ahertz frequency ranges. (C) 2000 American Institute of Physics. [S0021-897 9(00)01224-X].