Ballistic and quasiballistic tunnel transit time oscillators for the terahertz range: Linear admittance

Abstract

We have considered interactions between ballistic ͑or quasiballistic͒ electrons accelerated by a dc electric field in an undoped transit space ͑T space͒ and a small ultrahigh frequency ac electric field and have calculated the linear admittance of the T space. Electrons in the T space have a conventional, nonparabolic dispersion relation. After consideration of the simplest specific case when the current is limited by the space charge of the emitted electrons, we turned to an actual case when the current is limited by a heterostructural tunnel barrier ͑B barrier͒ separating the heavily doped cathode contact and the T space. We assumed that the B barrier is much thinner than the T space and both dc and ac voltages drop mainly across the T space. The emission tunnel current through the B barrier is determined by the electric field E(0) in the T space at the boundary B barrier/T space. The more substantial is, the tunnel current limitation the higher the electric field E(0) becomes. We have shown that for a space-charge limited current the change from parabolic dispersion to the nonparabolic branch induces narrowing and closing of the frequency windows of transit-time negative conductance starting with the lowest-frequency windows. These narrowing and closing frequency windows become effective only for very high voltages U across the T space: UӷmV S 2 /2e, where m is the effective mass for the parabolic branch and V S is the saturated velocity for the nonparabolic branch. For moderate voltages U, the effects of nonparabolicity are not very substantial. The tunnel current limitation decreases the space-charge effects in the T space and diminishes the role of the detailed electron dispersion relation. As a result, restoration of the frequency windows of transit-time negative conductance and an increase in the value of this negative conductance occur. The implementation of the considered tunnel injection transit time oscillator diode promises to lead to efficient and powerful sources of terahertz range radiation.

Time-dependent electron tunneling through time-dependent tunnel barriers

“…13 Also, the theory of ballistic TT diodes with a tunnel electron emission has been developed recently. [14][15][16] Such diodes can be designed as THz oscillators.…”

Graphene Tunneling Transit-Time Terahertz Oscillator Based on Electrically Induced p–i–n Junction

“…The tunneling generation through the zero energy gap and propagation of electrons and holes with their directed velocity v x close to the characteristic velocity v W ≃ 10 8 cm/s of the graphene energy spectrum (v x ∼ v W ), can provides significant advantages of G-TUNNETTs in comparison with the existing and discussed TUNNETTs based on the conventional semiconductor materials (see, for instance, Refs. [19,20] and the references therein). Using the developed device model, we calculate the high-frequency characteristics.…”

Phenomenological theory of tunnel emitter transit time oscillators for the terahertz range

“…͑1͒ the required JV-characteristic can be obtained numerically. 8 But the calculation is substantially simplified if the linear dispersion relation Eq. ͑2͒ is valid for the total electron beam across the whole T-space.…”

“…͑18͒ can be solved only numerically. 8 But in the specific case of the linearized relation ͑2͒, Eq. ͑18͒ is substantially simplified since m Ϫ1 (p) ϭ0 and we have…”