Coherent Emission in the Vicinity of 10 THz due to Auger-Suppressed Recombination of Dirac Fermions in HgCdTe Quantum Wells

Abstract

The discovery of Dirac fermions in a number of 2D and 3D materials boosted the solid-state research in an unprecedented way. Among the many hopes of using their exceptional physical properties, it has been argued that their reduced nonradiative losses would allow graphene to compete with quantum cascade lasers (QCLs) in the race for terahertz (THz) emitters. Unfortunately, the nonradiative Auger recombination (AR) process is still active for massless fermions in gapless graphene. However, for massive Dirac fermions, AR can be entirely suppressed below a certain threshold of the carrier’s kinetic energy that depends on the nonparabolicity and the symmetry of the electron and hole dispersions. In this work, by finely tuning the band structure of HgCdTe quantum wells hosting massive Dirac fermions, we set the electronic system below this threshold and demonstrate that the carrier recombination is purely radiative. A coherent interband emission reaching 9.6 THz, that is to say outside the spectral range of current QCLs, is measured under these conditions, opening the way to lossless interband THz emitters.

Photoluminescence spectroscopy of HgCdTe quantum well heterostructures in the 15-30 μm wavelength range

“…Studies with excitation by a pulsed CO 2 laser did not allow obtaining SE in this structure. On the other hand, it has been experimentally confirmed that SE at wavelength of ∼ 30 µm can be obtained under similar experimental conditions in structures with Auger process threshold of ∼ 20 meV [10]. Note that in both cases the threshold energy is much higher than the lattice temperature 8 K (which corresponds to the energy ∼ 1 meV), which should lead to strong suppression of Auger recombination if the carrier temperature is close to the lattice temperature.…”

“…Knowing the QW parameters, one can use numerical methods to estimate the efficiency of Auger recombination, which is one of the main factors hindering the production of long-wavelength SE. As was shown in the works [9,10], the efficiency of Auger recombination correlates with the value of the so-called threshold energy of the Auger process, which is uniquely determined by the band spectrum of the structure under study. The threshold energy is defined as the minimum kinetic energy, in which case a system of three particles can participate in the Auger process [11].…”

“…In this case, the energies of both transitions between the ground and excited states correspond to the PC spectra. The high content of Cd in the QW, as well as the use of relatively narrow-bandgap barriers (x Cd = 0.58), leads to the fact that the threshold Auger recombination is only 8 meV, which is practically 2 times less than in the structure described in the work [10].…”

“…The array (10 QWs) of HgCdTe quantum wells separated by wide-band CdHgTe light-blocking layers, which are the active region of the structures, is placed in waveguide layers. The active area is located at the antinode of the TE 0 -mode, localization of which occurs due to the gradient of the refractive index between the waveguide layers and between the waveguide layers and air [10].…”

Temperature dependence of the Fermi level in HgCdTe narrow-gap bulk films at different mercury vacancy concentrations

“…At the same time, the focus in the studies of such structures shifted to the area of effects caused by the law of dispersion of charge carriers and inversion of bands, in particular, the occurrence of the state of a topological insulator in two-dimensional [7] and three-dimensional structures [8] were shown, the presence of pseudo-relativistic particlesmassless Dirac fermions in massless QWs [9] and Kane fermions in volume CHT films [10][11][12]. CHT-based structures may prove to be a promising material for the creation of detectors and radiation sources in the far and medium infrared range, in particular, for designing of interband lasers [13,14] and for applications in the field of absorption and heterodyne spectroscopy with time resolution in long-wavelength part of the medium IR range (radiation wavelength is 9−30 µm).…”