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

Two groups of current carriers naturally coexist in ballistic and quasiballistic diodes and field-effect transistors (FETs): (1) traversing ballistic current carriers emitted by a source and absorbed by a drain, and (2) nontraversing (nonparticipating in a current flow) carriers that are in equilibrium 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 article, we consider development of the two-stream instability in n⁺ nn⁺ diodes with a doped bulk n-base, n⁺ nn⁺ diodes with a modulation doped n-channel base, and also in diodes with a gated n-channel base (that is in ballistic FETs) where a gate potential controls electron concentration in the channel. Since oscillatory regimes in such devices are restricted by pair electron-electron interaction between electrons belonging to the two different streams and participating in the instability process, we suggest a new type FET with two parallel n channels. Current-carrying electrons from the primary channel interact with slow electrons from the parallel additional channel that simultaneously serves as a controlling gate for the primary channel. In this design, electron streams participating in the two-stream instability are spatially separated, and their pair interaction is suppressed. Along with analytic estimates, we present results of numerical simulations for the ballistic FETs that prove the existence of oscillatory regimes in terahertz frequency ranges.