Plasmon absorption reduction in multiple quantum well structures.

The damping of two-dimensional plasmons in structures with several quantum wells due to absorption by free carriers is studied theoretically. Both gate structures and structures without a gate are considered. It is shown by the example of structures with GaAs quantum wells that an increase in the number of quantum wells while maintaining the electron concentration in each of them leads to a decrease in the damping coefficient of two-dimensional plasmons. The physical reasons for the decrease in the absorption of plasmons are discussed. It is shown that an increase in the number of quantum wells should lead to a decrease in the decay of plasmons in systems with a finite gate width as well.

Thin active region HgCdTe-based quantum cascade laser with quasi-relativistic dispersion law.

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.

Terahertz plasmons in doped HgTe quantum well heterostructures: dispersion, losses, and amplification.

We have calculated two-dimensional plasmon energy spectra in HgTe/CdHgTe quantum wells with normal, gapless, and inverted energy spectra with different electron concentrations, taking into account spatial dispersion of electron polarizability and plasmon interaction with the optical phonons. The spectra of the absorption coefficients of two-dimensional plasmons are found. It is shown that an increase of electron concentration in a quantum well leads to a decrease in the plasmon absorption coefficient. We have calculated the probabilities to recombine via the plasmon emission for nonequilibrium holes. The threshold concentrations of the nonequilibrium holes, above which the plasmon amplification is possible, have been calculated for various electron concentrations. It is shown that the presence of equilibrium electrons can significantly reduce the threshold hole concentration required for amplification of plasmon in the terahertz wavelength region. The dependencies of threshold hole concentration on electron concentration for different quantum wells are discussed. Gain spectra of the two-dimension plasmon are calculated.

Possibility of intracavity terahertz difference frequency generation in a two-frequency GaAsP/AlGaAs/GaAs quantum well laser.

We consider the GaAsP/AlGaAs/GaAs laser design with two different quantum wells for simultaneous generation of ${{\rm{TE}}_0}$ and ${{\rm{TM}}_0}$ modes having different frequencies in near-IR range. We theoretically investigate the possibility of effective difference frequency generation in the 7.5-8 and 10.5-11 THz regions in the laser design proposed. Resonant increase of second-order susceptibility in AlGaAs in these ranges provides sufficient generation efficiency. We demonstrate an output power-conversion factor for the difference frequencies in the 7.5-8 THz range to be up to ${{4 {-} 8}}\;{{\rm{MW}}^{- 1}}$ at room temperature in such a laser.

Threshold energies of Auger recombination in HgTe/CdHgTe quantum well heterostructures with 30-70 meV bandgap.

We calculate the threshold energies of Auger recombination in the HgTe/CdHgTe quantum well heterostructures with the bandgap in the 30-70 meV range. It is shown that there is a maximum in the temperature dependence of the threshold energy for Auger process involving two electrons and a hole. For Auger process involving two holes and an electron, in which the hole is in the second valence subband in the final state, the threshold energy decreases down to zero and then increases steeply as temperature grows. The results of calculation can be considered as guidelines for designing the long-wavelength laser structures.

Radiative recombination in narrow gap HgTe/CdHgTe quantum well heterostructures for laser applications.

Radiative recombination is studied in CdHgTe/HgTe QWs with bandgap in the 40-140 meV range using four-band Kane model. Calculated radiative lifetimes agree well with the photoconductivity kinetics measurements. We show that the side maxima in the valence band hinder the radiative recombination at high carrier concentrations and discuss how to overcome this effect for the development of long-wavelength lasers.

Stimulated emission in the 2.8-3.5 µm wavelength range from Peltier cooled HgTe/CdHgTe quantum well heterostructures.

We report stimulated emission in the 2.8-3.5 µm wavelength range from HgTe/CdHgTe quantum well (QW) heterostructures at temperatures available with thermoelectric cooling. The structures were designed to suppress the Auger recombination by implementing narrow (1.5 - 2 nm wide) QWs. We conclude that Peltier cooled operation is feasible in lasers based on such structures, making them of interest for spectroscopy applications in the atmospheric transparency window from 3 to 5 µm.

Electrically pumped InGaAs/GaAs quantum well microdisk lasers directly grown on Si(100) with Ge/GaAs buffer.

In this work we report, to the best of our knowledge, the first quantum well electrically-pumped microdisk lasers monolithically deposited on (001)-oriented Si substrate. The III-V laser structure was epitaxially grown by MOCVD on silicon with an intermediate MBE-grown Ge buffer. Microlasers with an InGaAs/GaAs quantum well active region were tested at room temperature. Under pulsed injection, lasing is achieved in microlasers with diameters of 23, 27, and 31 µm with a minimal threshold current density of 28 kA/cm2. Lasing spectrum is predominantly single-mode with a dominant mode linewidth as narrow as 35 pm.

Terahertz surface plasmons in optically pumped graphene structures.

We analyze the surface plasmons (SPs) propagating along optically pumped single-graphene layer (SGL) and multiple-graphene layer (MGL) structures. It is shown that at sufficiently strong optical pumping when the real part of the dynamic conductivity of SGL and MGL structures becomes negative in the terahertz (THz) range of frequencies due to the interband population inversion, the damping of the THz SPs can give way to their amplification. This effect can be used in graphene-based THz lasers and other devices. Due to the relatively small SP group velocity, the absolute value of their absorption coefficient (SP gain) can be large, substantially exceeding that of optically pumped structures with dielectric waveguides. A comparison of SGL and MGL structures shows that to maximize the SP gain the number of graphene layers should be properly chosen.