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The phonon modes of quantum-cascade heterostructures based on binary and ternary semiconductor compounds are simulated. The dependences of the frequencies of the structure interface phonon modes on the wave vector in the layer plane and on the phase shift in the superlattice period are calculated. It is found that the range of variation in the quantum energy of phonon modes of the GaAs/Al0.25Ga0.75As structure does not exceed 2 meV. The calculated resulting interband scattering rate in the structure, taking into account the interface and confined modes, barely differs from that calculated in the bulk phonon approximation.

The efficiency of electric pumping of THz quantum-cascade lasers (QCLs) with strip geometry is studied depending on the number and position of contact pads. The numerical simulation of the electric potential distribution in the THz QCL active region is used to determine the required thicknesses of the upper metallisation layers of the THz QCLs to minimize the voltage drop along the laser structure in the case of nonuniform current supply. It is found that the efficiency of electric pumping in the case of a centrally located contact is significantly higher than when the contact pads are located near the laser structure edges. From the calculated dependence of the THz QCL integral power on the thickness of the upper metal layer, it is shown that for effective current injection, the contact pads must be located at a distance of less than 0.5 mm from each other.

We investigate the light-current-voltage characteristics and emission spectra of 2.3 THz quantum cascade laser operating in the negative differential resistance (NDR) region. It was shown that the formation of electric field domains (EFDs) leads to a large number of discontinuities on the current-voltage and the total optical power on current characteristics. Measurements of emission spectra at different current (before the NDR region and in the NDR region) shows that the formation of EFDs results in decrease of the output intensity, but does not influence on Fabry-Perot multi-mode structure of THz QCL. The developed theoretical model predicts the formation of EFDs in the NDR region and qualitatively explain the experimental results.

HgCdTe is promising as a material to solve a problem of the development of semiconductor sources with an operational frequency range of 6–10 THz due to the small optical phonon energies and electron effective mass. In this study, we calculate the dependence of the metal–metal waveguide characteristics on the number of cascades for the 3-well design HgCdTe-based quantum cascade laser at 8.3 THz. It is shown that four cascades are sufficient for lasing at a lattice temperature of 80 K due to the large gain in the active medium. The results of this study provide a way to simplify the fabrication of thin active region HgCdTe-based quantum cascade lasers for operation in the range of the GaAs phonon Reststrahlen band inaccessible to existing quantum cascade lasers.

A model based on a system of balance equations for localised and continuum states is developed to calculate the current − voltage (I − V) and power characteristics of quantum-cascade lasers (QCLs) operating in the terahertz (THz) range. A method for modifying the eigenbasis of the Schrödinger equation by reducing the dipole moments of tunnel-coupled states is proposed to take into account the effect of dephasing on the carrier transport. The calculated and experimental data on the current − voltage characteristics and the dependence of the integrated radiation intensity on current for the THz QCLs lasing at 2.3 THz are compared. The calculated and measured values of the threshold current, lasing current range, and maximum operating temperature T max are found to be in good agreement. It is shown that T max can be increased by 25 % by reducing the thickness of the top contact layer n +-GaAs of the laser structure under study from 800 to 100 nm.

The effect of nonlinear gain mechanisms, such as dynamic heating of carriers by radiation, and burnup of spatial and spectral gaps, on the real and imaginary parts of the refractive index is examined. The dependence of the effective amplitude–phase coupling parameter for nonlinear gain on emission frequency and pump level is established. Dynamic heating is shown to be the main mechanism for the nonlinear gain determining the above parameter.

We propose an electrically pumped laser diode based on multiple HgTe quantum wells with band structure engineered for Auger recombination suppression. A model for accounting for hot phonons is developed for calculating the nonequilibrium temperature of electrons and holes. Using a comprehensive model accounting for carrier drift and diffusion, Auger recombination, and hot-phonon effects, we predict of lasing at [Formula: see text] [Formula: see text]m at room temperature in the 2.1 nm HgTe/Cd[Formula: see text]Hg[Formula: see text]Te quantum well heterostructure. The output power in the pulse can reach up to 600 mW for 100 nanosecond-duration pulses.

We have designed and fabricated 2.3 THz QCL with active module based on 4 QWs GaAs/Al0.15Ga0.85As. The light-current-voltage (L-I-V) characteristics and emission spectra of fabricated THz QCL are investigated. The nonmonotonic behavior of L–I characteristic and a large number of discontinuities in I-V characteristic is observed. Our calculations show that such electric instabilities are associated with the field inhomogeneity across the active region (electric field domains). We investigate transmission spectra of incident radiation of GaAs and AlGaAs/GaAs structures with two highly absorption optical response regions. Thus, to improve the performance and extend the operation frequencies of THz QCLs it is needed to develop new concepts of active region designs for avoiding the formation of electric field domains and employ novel material systems for lasing in the frequency range 8-11 THz.