On the effect of the electron distribution in the near-contact region and asymmetry of the resonant-tunneling diode structure on the high-frequency response and the possibility of detecting the quantum amplification mode in an external high-frequency electric field

The conditions of the implementation of the quantum mode of microwave generation in semiconductor resonant-tunneling diode (RTD) structures were theoretically analyzed. The high-frequency response in structures with symmetric and asymmetric barriers was analyzed by numerical simulation methods. The effect of the Fermi distribution of carriers in the near-contact region was studied. It was shown that asymmetric structures with decreased impurity concentrations (10¹⁷ cm^?3) in the emitter region are optimum from the viewpoint of experimental observation of the quantum amplification mode.     

Magnetotunneling spectroscopy of polarons in a quantum well of a resonant-tunneling diode

Resonant tunneling of electrons is thoroughly studied in in-plane magnetic fields. Anticrossing is revealed in a spectrum of two-dimensional electrons at energies of optical phonons. The magnetic field changes the momentum of tunneling electrons and causes a voltage shift of a resonance in the tunnel spectra in accordance with the electron dispersion curve. Anticrossing is clearly observed in second derivative current-voltage characteristics of a resonant tunneling diode made of a double-barrier Al_0.4Ga_0.6As/GaAs heterostructure.     

High-frequency response and the possibilities of frequency-tunable narrow-band terahertz amplification in resonant tunneling nanostructures

The characteristics of the high-frequency response of single- and double-well resonant tunneling structures in a dc electric field are investigated on the basis of the numerical solution of a time-dependent Schrödinger equation with open boundary conditions. The frequency dependence of the real part of high frequency conductivity (high-frequency response) in In_0.53Ga_0.47As/AlAs/InP structures is analyzed in detail for various values of the dc voltage V _dc in the negative differential resistance (NDR) region. It is shown that double-well three-barrier structures are promising for the design of terahertz-band oscillators. The presence of two resonant states with close energies in such structures leads to a resonant (in frequency) response whose frequency is determined by the energy difference between these levels and can be controlled by varying the parameters of the structure. It is shown that, in principle, such structures admit narrow-band amplification, tuning of the amplification frequency, and a fine control of the amplification (oscillation) frequency in a wide range of terahertz frequencies by varying a dc electric voltage applied to the structure. Starting from a certain width of the central intermediate barrier in double-well structures, one can observe a collapse of resonances, where the structure behaves like a single-well system. This phenomenon imposes a lower limit on the oscillation frequency in three-barrier resonant tunneling structures.     

On the amplification of optical signal in structures with quantum dots

We consider a possibility to use structures with quantum dots as media for the amplification of a weak optical signal. It is shown that in such structures a transition from absorption to amplification is possible without creation of the population inversion.     

Study on the current bistability and hysteresis in resonant-tunneling structures

We present a time-dependent quantum-kinetic study for the non-equilibrium electron transport properties of double-barrier resonant-tunneling devices. The approach is based on a self-consistent solution of Wigner equation and Poisson equation. We find intrinsic current fluctuations around the current turning point. These instabilities lead to three current irreversible regions, two current hystereses and one small inverse current change in the valley position of current, for the forward and backward bias sweep. The bias step applied on the device affects the width of each current irreversible regions and the current peak height of the middle region.     

Nonlinear quantum mode of terahertz electromagnetic wave amplification in resonant tunneling heterostructures

An analysis of high-frequency properties of the resonant tunneling diode (RTD) in a strong microwave electromagnetic field showed that the high-frequency current response increasing with the microwave power significantly more rapidly saturates out in the case of classical amplification mode, than in the case of “quantum” amplification mode. This makes the “quantum” mode even more attractive in comparison with the classical mode from the viewpoint of the possibility of amplification and generation in the range of subterahertz and terahertz frequencies and offers new opportunities to advance towards these frequencies.     

On the possibility of detecting superheavy quasimolecules

The formation of superheavy electronic quasimolecules leads to measurable deviations from the Rutherford cross section in heavy ion collisions. For the system ²³⁸₉₂U-²³⁵₉₂U with E_c.m. = 800 MeV we find an average correction of 1.5% for the scattering cross section in forward directions. Additional background contributions like electronic shielding of the nucleus, vacuum polarization, nuclear Coulomb excitation and static deformations of the nuclei are taken into account.     

Temperature dependent nonlinear response of quantum cascade structures

Current response and gain spectrum of a terahertz quantum cascade laser is analyzed at different temperatures by a nonequilibrium Green’s functions approach. The simulations are compared to recent results of time domain spectroscopy. Being able to retrieve higher harmonics of the response function, nonlinear phenomena in quantum cascade lasers are studied theoretically. For different temperatures, gain is simulated under operating conditions and related to the intensity inside the cavity, showing the degradation of performance with temperature. Resolving the electron densities in energy shows the breakdown of inversion at high intensities.     

Energy filtration effect and the possibility of the generation of terahertz radiation in resonant tunneling structures with several quantum wells

The properties of a high-frequency response in resonant tunneling double-well nanostructures have been considered for various energies of electrons arriving to a structure of electrons, various frequencies of the external electromagnetic field, and various features associated with the interaction of electronic states in neighboring quantum wells in double-well nanostructures. The energy filtration effect that is caused by the breaking of the symmetry of the high-frequency response in double-well nanostructures in a static electric field has been revealed. This effect leads to a sharp increase in the gain under conditions of the quantum amplification regime and opens real prospects of a significant increase in the efficiency of solid amplifying and generating devices based on resonant tunneling double-well nanostructure in the subterahertz and terahertz frequency ranges.     

On the possibility of detecting low-energy scalar and pseudo-scalar bosons

The properties of the conversion of “cold” extra-light scalar or pseudo-scalar bosons weakly interacting with material media to photons with energies of 0.001–1.0 meV are analyzed. Various possible experimental schemes including closed resonant cells at low temperatures and highly sensitive receivers of radio-frequency photons are presented. The existence of such elementary particles is predicted in various expansion versions of the “standard model”. Their direct or indirect detection would make it possible to clarify the nature of the “dark matter” phenomenon.