A. V. Ikonnikov

Cyclotron resonance and interband optical transitions in HgTe/CdTe(0 1 3) quantum well heterostructures

Cyclotron resonance spectra of 2D electrons in HgTe/CdxHg1−xTe (0 1 3) quantum well (QW) heterostructures with inverted band structure have been thoroughly studied in quasiclassical magnetic fields versus the electron concentration varied using the persistent photoconductivity effect. The cyclotron mass is shown to increase with QW width in contrast to QWs with normal band structure. The measured values of cyclotron mass are shown to be systematically less than those calculated using the 8 × 8 Kane model with conventional set of HgTe and CdTe material parameters. In quantizing pulsed magnetic fields (Landau level filling factor less than unity) up to 45 T, both intraband (CR) and interband magnetoabsorption have been studied at radiation wavelengths 14.8 and 11.4 µm for the first time. The results obtained are compared with the allowed transition energies between Landau levels in the valence and conduction bands calculated within the same model, the calculated energies being again systematically less (by 3–14%) than the observed optical transition energies.

Cyclotron resonance in HgTe/CdTe-based heterostructures in high magnetic fields

AbstractCyclotron resonance study of HgTe/CdTe-based quantum wells with both inverted and normal band structures in quantizing magnetic fields was performed. In semimetallic HgTe quantum wells with inverted band structure, a hole cyclotron resonance line was observed for the first time. In the samples with normal band structure, interband transitions were observed with wide line width due to quantum well width fluctuations. In all samples, impurity-related magnetoabsorption lines were revealed. The obtained results were interpreted within the Kane 8·8 model, the valence band offset of CdTe and HgTe, and the Kane parameter EP being adjusted.

Terahertz spectroscopy of quantum-well narrow-bandgap HgTe/CdTe-based heterostructures

The energy spectra of quantum-well narrow-bandgap Hg1 − yCdyTe/CdxHg1 − xTe heterostructures have been studied. The dependences of the effective cyclotron mass on the density (in classical magnetic fields) and the transition energy (in quantizing fields) have been obtained from the cyclotron resonance measurements. These dependences confirm the near-linear dispersion law for the electrons with small mass at the band bottom (the minimum cyclotron mass measured is 0.003 m0). The interband photoconductivity of the CdHgTe-based structures with the long-wavelength photoresponse edge lower than 6 meV has been demonstrated.

Spin Splitting in HgTe/CdHgTe (013) Quantum Well Heterostructures

The electron transport and cyclotron resonance in a one-sided selectively doped HgTe/CdHgTe (013) heterostructure with a 15-nm quantum well with an inverted band structure have been investigated. The modulation of the Shubnikov-de Haas oscillations has been observed, and the spin splitting in zero magnetic field has been found to be about 30 meV. A large Δmc/mc ≃ 0.12 splitting of the cyclotron resonance line has been discovered and shown to be due to both the spin splitting and the strong nonparabolicity of the dispersion relation in the conduction band.

Exchange enhancement of the g factor in InAs/AlSb heterostructures

The evolution of the Shubnikov-de Haas oscillations in InAs/AlSb heterostructures with twodimensional electron gas in InAs quantum wells 12–18 nm wide with considerable variation in the electron concentration (3–8) × 1011 cm−2 due to the effect of negative persistent photoconductivity is studied. The values of the effective Landé factor for electrons g* = −(15–35) are determined. It is shown that the value of the g* factor increases as the quantum well width increases.

Temperature-driven single-valley Dirac fermions in HgTe quantum wells

We report on the temperature-dependent magnetospectroscopy of two HgTe/CdHgTe quantum wells below and above the critical well thickness dc. Our results, obtained in magnetic fields up to 16 T and s temperature range from 2 to 150 K, clearly indicate a change in the band-gap energy with temperature. A quantum well wider than dc evidences a temperature-driven transition from topological insulator to semiconductor phases. At a critical temperature of 90 K, the merging of inter- and intraband transitions in weak magnetic fields clearly specifies the formation of a gapless state, revealing the appearance of single-valley massless Dirac fermions with a velocity of 5.6×105ms−1. For both quantum wells, the energies extracted from the experimental data are in good agreement with calculations on the basis of the eight-band Kane Hamiltonian with temperature-dependent parameters.

Cyclotron resonance study in InAs/AlSb quantum well heterostructures with two occupied electronic subbands

We report on the cyclotron resonance (CR) study in InAs/AlSb (001) quantum well (QW) heterostructures with two occupied electronic subbands. Experimental results are compared with the CR energy calculations in the self-consistent Hartree approximation. Our theoretical approach is based on the 8-band k · p Hamiltonian and takes into account the band nonparabolicity, lattice-mismatch deformation, and spin-orbit coupling. We find out a large splitting of CR line associated with a difference in cyclotron energies in the first and second electronic subbands. The results of CR study in InAs/AlSb QW heterostructures reveal pronounced effect of the “built-in” electric field on CR spectra in the samples with two occupied electronic subbands.

Long-wavelength injection lasers based on Pb1–x Sn x Se alloys and their use in solid-state spectroscopy

Diffusion lasers based on Pb1–xSnxSe alloys for a wide spectral range (7–40 μm) are developed. The emission spectra of these lasers in the temperature range of 18–80 K are investigated. It is shown that the laser-emission wavelength can be widely tuned by varying the operation temperature, which allows a spectral range of 7–26 THz to be covered. The possibility of using these lasers for the spectroscopy of solids, and, in particular, for the magnetooptical spectroscopy of narrow-gap semiconductor structures based on HgCdTe, is demonstrated.

Specific features of the spectra and relaxation kinetics of long-wavelength photoconductivity in narrow-gap HgCdTe epitaxial films and heterostructures with quantum wells

The spectra and relaxation kinetics of interband photoconductivity are investigated in narrow-gap Hg1 − xCdxTe epitaxial films with x = 0.19–0.23 and in structures with HgCdTe-based quantum wells (QWs), having an interband-transition energy in the range of 30–90 meV, grown by molecular-beam epitaxy on GaAs (013) substrates. A long-wavelength sensitivity band caused by impurities or defects is found in the spectra of the structures with quantum wells in addition to the interband photoconductivity. It is shown that the lifetimes of nonequilibrium carriers in the structures with QWs is less than in bulk samples at the same optical-transition energy. From the measured carrier lifetimes, the ampere-watt responsivity and the equivalent noise power for a film with x = 0.19 at a wavelength of 19 μm are estimated. When investigating the relaxation kinetics of the photoconductivity at 4.2 K in high excitation regime, it is revealed that radiative recombination is dominant over other mechanisms of nonequilibrium-carrier recombination.

Spectra of persistent photoconductivity in InAs/AlSb quantum-well heterostructures

Persistent photoconductivity at T = 4.2 K in AlSb/InAs/AlSb heterostructures with two-dimensional (2D) electron gas in InAs quantum wells is studied. Under illumination by IR radiation (ℏω = 0.6–1.2 eV), positive persistent photoconductivity related to the photoionization of deep-level donors is observed. At shorter wavelengths, negative persistent photoconductivity is observed that originates from band-to-band generation of electron-hole pairs with subsequent separation of electrons and holes by the built-in electric field, capture of electrons by ionized donors, and recombination of holes with 2D electrons in InAs. It is found that a sharp drop in the negative photoconductivity takes place at ℏω > 3.1 eV, which can be attributed to the appearance of a new channel for photoionization of deep-level donors in AlSb via electron transitions to the next energy band above the conduction band.