A. V. Antonov

Study of lifetimes and photoconductivity relaxation in heterostructures with HgxCd1 − xTe/CdyHg1 − yTe quantum wells

Carrier lifetimes in the continuum of the quantum well of a HgxCd1 − xTe/CdyHg1 − yTe hetero-structure were studied by terahertz pump-probe spectroscopy. It is found that the relaxation duration of the transmission signal is ∼65 ps and is independent of the pump power. Such rapid relaxation in these structures is most likely determined by the interaction of holes with acoustic phonons due to a high density of states in the valence band and a larger effective mass compared with electrons. By the obtained data, the times of the interband nonradiative recombination of holes are determined. In this publication, we report the results of numerical calculation of the energy spectrum of the model structure, in which the possibility of obtaining population inversion at specified concentrations of nonequilibrium carriers is analyzed.

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.

Spectra and kinetics of THz photoconductivity in narrow-gap Hg1?xCdxTe (x < 0.2) epitaxial films

Investigation into far infrared photoconductivity (PC) in narrow-gap epitaxial bulk Hg1–xCdxTe (x < 0.2) films grown by molecular beam epitaxy and chemical vapor deposition techniques is presented. A broadband of photosensitivity in terahertz region is found at 4.2 and 77 K. Some long-wavelength peculiarities of spectra are discovered and their origins are discussed. We also study PC relaxation process with nanosecond time resolution. It is found that carrier relaxation is non-radiative and measured lifetimes show that some of the structures are applicable for detecting in very long-wavelength infrared range.

Experimental study of frequency multipliers based on a GaAs/AlAs semiconductor superlattices in the terahertz frequency range

Frequency multipliers based on a GaAs/AlAs semiconductor quantum superlattice have been experimentally studied. The power spectrum of the harmonics in the output signal from a multiplier with an input-signal frequency of 140–160 GHz has been measured. Planar diodes with a small active region (an area of 1–2 μm2) have been used in this study. For fabrication of the diodes, structures of heavily doped superlattices with the miniband width 24 meV have been used, these structures were grown by the molecular-beam epitaxy method. Measurements have been conducted using a BOMEM DA3.36 Fourier spectrometer equipped with a detector based on a bolometer cooled to the temperature of liquid helium. The results of the measurements have been used to plot the dependences of the power of the harmonics on the frequency in the range from 0.4 to 8.1 THz. It has been found that the character of the microwave-power distribution over the number of harmonics is close to the spectrum of a sequence of sign-alternating pulses which appear in the diode circuit when the applied voltage of the input signal exceeds the threshold of the diode. The minimal time of establishment of the pulse front and pulse duration are equal to 123 and 667 fs, respectively.

Electron Transport and Terahertz Radiation Detection in Submicrometer-Sized GaAs/AlGaAs Field-Effect Transistors with Two-Dimensional Electron Gas

The electronic transport and response in the terahertz range are studied in field-effect GaAs/AlGaAs transistors with a two-dimensional high-mobility electron gas. The special interest expressed in such transistors stems from the possibility of developing terahertz-range radiation detectors and generators on the basis of these devices. Measurements of the value and the magnetic-field dependence of the drain-source resistance are used to estimate the electron density and mobility in the transistor channel. Results of magnetotransport measurements are employed to interpret the nonresonant detection observed in transistors with a gate width from 0.8 to 2.5 µm.

SiGe nanostructures with self-assembled islands for Si-based optoelectronics

The effect of structure parameters on the electroluminescence and photoconductivity of multilayer structures with self-assembled Ge(Si)/Si(0 0 1) islands has been studied. The highest intensity of the room-temperature electroluminescence in the wavelength range of 1.3–1.55 µm has been observed for the islands grown at 600 °C. The same diode structures with Ge(Si)/Si(0 0 1) islands have demonstrated room-temperature photoconductivity signals in the wavelength range of 1.3–1.55 µm. The observed overlap of the electroluminescence and photoconductivity spectra obtained for the same structures with Ge(Si) islands makes these structures a promising material for the fabrication of a Si-based optocoupler. Less degradation after neutron irradiation has been observed for the electroluminescence and photoconductivity signals from multilayer structures with Ge(Si) self-assembled islands in comparison with bulk silicon structures. This result is associated with more effective confinement of charge carriers in the multilayer structures with Ge(Si) islands.

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.

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.

Long wavelength stimulated emission up to 9.5 μm from HgCdTe quantum well heterostructures

Stimulated emission from waveguide HgCdTe structures with several quantum wells inside waveguide core is demonstrated at wavelengths up to 9.5 μm. Photoluminescence line narrowing down to kT energy, as well as superlinear rise in its intensity evidence the onset of the stimulated emission, which takes place under optical pumping with intensity as small as ∼0.1 kW/cm2 at 18 K and 1 kW/cm2 at 80 K. One can conclude that HgCdTe structures potential for long-wavelength lasers is not exhausted.

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.