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

Abstract

We develop an analytic theory based on an earlier model of the admittance of a ballistic transit time diode terahertz oscillator with tunnel emission of electrons into a transit space. The focus of this work is on the actual case when electrons are injected with high enough energy to move from the start with maximal ͑saturated͒ ballistic velocity (ϳ1ϫ10 8 to 2ϫ10 8 cm/s). On the one hand, such diodes have maximal oscillation frequencies and, on the other hand, a simple analytic theory describes them and allows us to avoid a cumbersome numerical procedure, which characterizes the general case. Such a description is analogous to the description of oscillatory diodes with diffusive transport and saturated drift velocity. We have also considered a special case when a small part of the ballistic electrons crossing the transit space scatter into a diffusive subsystem with a small drift velocity. The appearance of such slow-drifting electrons substantially increases space charge in the transit space and influences the static JV-characteristic but the high-frequency admittance is almost invariable.

Time-dependent electron tunneling through time-dependent tunnel barriers

“…3) can differ from the barrier effective mass m (such a situation corresponds to the structure considered in Ref. 16). We also foresee a possible lowering of the conduction band bottom in region 2 (as in Fig.…”

“…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.…”

Wide gap semiconductor microwave devices

“…Transit-time diodes with a tunnel electron emitter are in principle the highestspeed transit-time diodes and are appropriate for the terahertz range oscillatory regime. In contrast to their IMPATT-and BARITT-competitors, they can be completely ballistic devices since the principle of action inherent in them does not require any dissipative processes either in a tunnel barrier or in a transit space [46,47]. Taking into account physical phenomena, accompanying a hybrid regime between the tunnelling effects and avalanche ionization, is also a difficult problem.…”

“…Here we expect an increase in the amplitude of the microwave signal, all other factors being equal. As is well known [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], the negative dynamic resistance (NDR) effects may be enhanced in transit-time devices if the phase lag of the modulation component of the current, which is in anti-phase with the local electric field, is increased. For this reason, the use of SiC is promising also owing to the fact that the charge mobility in the SiC polytypes is rather small, which should lead to an increase in the phase delay between the current and the alternating electric field in the microwave range and, hence, to an increase in the absolute magnitude of NDR and available microwave power (see, for example, figure 11 [36,37]).…”