K. V. Maremyanin

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.

Efficient long wavelength interband photoluminescence from HgCdTe epitaxial films at wavelengths up to 26 μm

Photoluminescence (PL) and photoconductivity (PC) studies of Hg1−xCdxTe (0.19 ≤ x ≤ 0.23) epitaxial films are presented. Interband PL is observed at wavelengths from 26 to 6 μm and in the temperature range 18 K–200 K. The PL line full width at half maximum is about 6 meV (4kT) at 18 K and approaches its theoretical limit of 1.8kT at higher temperatures. Carrier recombination process is also investigated by time resolved studies of PL and PC at pulsed excitation. Radiative transitions are shown to be the dominating mechanism of carrier recombination at high excitation levels.

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.

Time resolved photoluminescence spectroscopy of narrow gap Hg1−xCdxTe/CdyHg1−yTe quantum well heterostructures

Photoluminescence (PL) spectra and kinetics of narrow gap Hg1−xCdxTe/CdyHg1−yTe quantum well (QW) heterostructures grown by molecular beam epitaxy technique are studied. Interband PL spectra are observed from 18 K up to the room temperature. Time resolved studies reveal an additional PL line with slow kinetics (7 μs at 18 K) related to deep defect states in barrier layers. These states act as traps counteracting carrier injection into QWs. The decay time of PL signal from QW layers is about 5 μs showing that gain can be achieved at wavelengths 10–20 μm by placing such QWs in HgCdTe structures with waveguides.

Room-temperature intracavity difference-frequency generation in butt-joint diode lasers

We obtain, for the first time to our knowledge, the room-temperature intracavity difference-frequency generation in the mid-infrared range (around 10 mum wavelength) in a butt-joint GaAs/InGaAs/InGaP quantum-well dual-wavelength laser diode which supports lasing at two closely spaced wavelengths in the near-infrared range close to 1 mum. We employ a special asymmetric waveguide design (which makes it possible the different-order transverse-mode lasing) and a low-doped substrate that minimize mid-infrared losses and phase mismatch for the difference-frequency nonlinear-mixing process. We explain qualitatively the physics of the intracavity mode mixing and describe in detail the design of the butt-joint diode laser. We show how to scale the effect into the far-infrared (terahertz) range, to improve the phase-matching conditions, and to enhance further the difference-frequency generation efficiency (the latter is about 1 W/(kW)2 in our first experiment).

Nonlinear mode mixing in dual-wavelength semiconductor lasers with tunnel junctions

The authors demonstrate and study two- and three-wavelength generations in the semiconductor diode laser with a tunnel junction separating two different quantum-well active regions integrated within a single waveguide. To avoid resonant cross absorption of the modes at different frequencies and achieve phase matching, the laser waveguide is designed to generate the first-order transverse mode at a longer wavelength and the third-order mode at a shorter wavelength. Excellent agreement with the designed and measured device parameters is observed. Intracavity nonlinear mixing leading to sum-frequency and second-harmonic generation is demonstrated.

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.

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.

Features of the persistent photoconductivity in InAs/AlSb heterostructures with double quantum wells and a tunneling-transparent barrier

The spectra of persistent photoconductivity for InAs/AlSb heterostructures with double quantum wells and a separation AlSb barrier with varying thickness between 0.6–1.8 nm are measured at T = 4.2 K. The electron concentrations in the wells at various illumination wavelengths are determined from the Fourier analysis of Shubnikov-de Haas oscillations. The features associated with the tunneling transparency of a separation barrier 0.6 nm thick (two monolayers) are revealed. The performed self-consistent calculations of the energy profile of a double quantum well showed that a symmetric profile is established in the structures in the region of negative residual photoconductivity, while the region of positive persistent photoconductivity has an asymmetric potential profile, which leads to Rashba spin splitting (>2 meV at the Fermi level). It is shown that the introduction of the tunneling-transparent separation barrier increases the Rashba splitting.

Rashba spin splitting and cyclotron resonance in strained InGaAs/InP heterostructures with a two-dimensional electron gas

Cyclotron resonance and magnetic transport in InP/InGaAs/InP heterostructures with axially symmetric quantum wells are studied experimentally at 4.2 K. An increase in the cyclotron mass at the Fermi level from 0.047m0 to 0.057m0 with an increase in the concentration of two-dimensional electrons from 5.5 × 1011 to 2.1 × 1012 cm−3 is shown. The values of the Rashba spin splitting at the Fermi level are determined from Fourier analysis of the beats of Shubnikov-de Haas oscillations. The obtained experimental data are compared with the theoretical results of self-consistent calculations of the energy spectrum and cyclotron masses of 2D electrons performed using the eight-band k · p Hamiltonian.