Z. S. Gribnikov

TUNNEL-JUNCTION-CONNECTED DISTRIBUTED-FEEDBACK VERTICAL-CAVITY SURFACE-EMITTING LASER

An injection distributed-feedback vertical-cavity surface-emitting laser (VCSEL) with tunnel junctions served as quasi-Ohmic intercontacts (tunnel-junction-connected distributed-feedback VCSEL) is proposed. A periodic structure of vertically stacked double-heterostructure laser diodes connected by low-resistance tunnel junctions forms a vertical distributed-feedback (DFB) laser medium. To minimize the threshold, the DFB structure is placed in a Fabry–Perot cavity designed to match gain layers with the maximums of the optical mode, and the tunnel junctions—with its minimums. The passive regions with tunnel junctions provide effective vertical injection into each active region of this multiple-active-region laser. This DFB VCSEL is expected to have an improved performance, specifically, reduced threshold current and heightened output power.

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

We have considered interactions between ballistic (or quasiballistic) electrons accelerated by a dc electric field in an undoped transit space (T space) 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 barrier) 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 ...

Two mechanisms of the negative-effective-mass instability in p-type quantum well-based ballistic p+pp+-diodes: Simulations with a load

There exist two regimes of the negative-effective-mass (NEM) instability in ballistic p+pp+-diodes with two-dimensional hole gas in the p-base: the instability of homogeneous NEM-hole distribution in a quasineutral plasma region, and the instability of a thin accumulation layer, which forms inside a depletion region and contains NEM holes. Both instabilities lead to the development of terahertz oscillatory regimes. The regimes’ simulation in the inductance-loaded diodes with base lengths 0.05–0.15 μm demonstrates that such loads substantially enlarge the voltage range of the second regime and give rise to oscillatory regimes, which do not appear in unloaded diodes at all. Efficiencies of different oscillatory regimes are estimated.

Gated negative-effective-mass ballistic terahertz generators

We consider gate control of terahertz generation in planar ballistic diodes with a negative-effective-mass section in a dispersion relation of current carriers in a current-conducting channel. Such a generation in ballistic p+pp+ or n+nn+ diodes occurs as a result of plasma instability development and self-organization of a regular oscillation regime. Conditions of existence and oscillation frequencies are calculated. The gate can also serve as an oscillation-collecting electrode. We consider double-gate designs, side by side with conventional single-gate designs. The double-gate devices allow us to separate circuits for direct and high-frequency currents.

Negative-effective-mass ballistic field-effect transistor: Theory and modeling

We consider p+pp+ diodes, in which the middle p region (base) consists of a p-type quantum well current-conducting channel that is controlled by a gate potential. Hole concentrations in the channel are assumed to be such that a ballistic current flows only in the lowest quantized subband. This subband contains a negative-effective-mass (NEM) section in the dispersion relation. We carry out numerical simulation for realistic designs of this ballistic field-effect transistor (FET) and compare them to simple analytical estimates. We show that three types of self-organized terahertz current oscillations appear in these FETs. Two of these types originate from the NEM instability, while the third arises from the two-stream instability, predicted before for conventional ballistic diodes and FETs. Frequencies of the NEM oscillations are controlled effectively by a gate potential. They are substantially higher than frequencies of two-stream oscillations. The NEM oscillation frequencies exceed 2.5 THz for large enh...

Generation of Terahertz Electric Oscillations by Ballistic Quantized Holes with Negative Effective Mass

The dispersion relation for the ground subband of quantized holes in a quantum well (QW) of zink-blende-like semiconductors contains an extensive section with negative effective mass (NEM). Under certain biases, stationary concentration distributions of the ballistic quantized holes in p+pp+-structures hold a self-organized region where holes with NEM predominate. The existence of such region causes a global instability of the entire stationary regime and the appearance of an oscillatory regime. We describe the dependence of the oscillatory regime on material and geometric parameters of the structure and consider factors that influence the oscillation frequency. The typical frequencies for 0.1 μm-structures are in the terahertz range (1-2 THz). The ballistic NEM-diodes have been classified as short, medium and long diodes depending on their oscillatory portrait. A new high-voltage region of oscillations that was not analytically predicted in early works is revealed in the so-called medium and long diodes. The region appears side by side with the stable stationary regime at high voltages. Switching between oscillatory and stationary regimes is studied.We also discuss the feasibility of ballistic transport of quantized holes in GaAs/AlAs p-QWs and substantiate a method of computer plotter of characteristics for a description of nonstationary processes.

Negative effective mass mechanism of negative differential drift velocity and terahertz generation

The negative-differential-drift-velocity instability, which forms the basis of Gunn high-frequency generators, can originate from Ridley-Watkins-Hilsum or negative effective mass (NEM) mechanisms. The first mechanism is dissipative by nature. The second is mainly drift-related. Therefore, the second mechanism promises to be more effective. We show the existence of stationary oscillatory regimes in the ballistic NEM p/sup +/ p p/sup +/-diodes, which have a base in the form of a periodic system of parallel p-type quantum-well channels with base length up to 30 nm. An oscillation frequency, which depends on the base length, doping, and spatial period, as well as loads and voltage across the diode, ranges from /spl les/1 to 5 THz. We propose an additional combined quantum GaAs-AlGaAs-heterostructure, which can be overgrown on a cleaved edge of a specially grown wafer. This structure is intended to obtain electron dispersion relations with NEM sections in the useful energy range of 0.1-0.25 eV.

The tunnel diode as a thyristor emitter

Abstract We propose a tunnel switching mechanism for a thyristor. This mechanism can be realized if a tunnel pn-junction is used as the thyristor emitter. The switching current is fully determined by a junction peak tunnel current and weakly depends on temperature. Thus stabilization of the thyristors switching and holding currents can be accomplished in a new way. The device voltage exhibits discontinuities as the device turns on. Results of numerical simulation of the tunnel emitters effects on the thyristors I – V characteristics are presented.

Quantum real-space transfer in a heterostructure overgrown on the cleaved edge of a superlattice

A dispersion relation for an electron in a two-layer (and also multilayer) quantum well (QW) is formed as a result of a certain combination of initial dispersion relations for each of the forming layers. Such a combination can be used to engineer new dispersion relations with desirable properties. The same relates to a two-dimensional electron gas (2DEG) induced in a multilayer medium. In this study, we consider first such a 2DEG in a specific two-layer structure where a superlattice (SL) plays the role of the second half-infinite layer, and electrons with large wave numbers along the SL vector spread from the first ordinary QW layer to this SL. As a result of such a quantum (dynamic) real-space transfer, electrons become heavier, and the dispersion relation achieves an additional negative effective mass (NEM) section. Such NEM dispersion relations were studied for several different material systems, including the two most interesting three-material systems: (1) an isomorphic Al0.15Ga0.85As//GaAs/Al0.5Ga0...

Stacked PIN diode structures for microwave switching

A diode structure consisting of several stacked PIN diodes with tunnel junctions serving as quasi-Ohmic intercontacts is proposed. This structure is preferable if a microwave switch is required to have both high breakdown voltage and very small switching time. In this case a conventional (single-base) PIN switch has too large forward voltage drop across the base at suAciently high current densities, because the base length is much greater than the bipolar diAusion length. This leads to high electric fields in the base and the development of unwelcome hot-electron eAects. The replacement of the long base with several narrow bases connected in series by heavily doped p + n + tunnel inserts solves this problem eAectively. Direct numerical calculations have shown that this stacked structure exhibits a substantially smaller DC forward voltage drop at the same switching times (or substantially smaller switching times at the same DC forward voltage drops). At the microwave frequency range, the resistance of the stacked structure can be decreased drastically because all the newly formed pn-junctions are shorted by their large capacitances. # 1999 Elsevier Science Ltd. All rights reserved.