Vol 50, No 10 (2016)

The temperature dependences of the electrical conductivity σ(T), the Hall coefficient R(T), and the thermoelectric coefficient α(T) are investigated in TlIn_1–xYb_xTe₂ (0 < x < 0.10) solid solutions at 80–1000К. From the kinetic parameters, the effective masses of electrons and holes are determined. The obtained experimental data on σ(T) and α(T) are interpreted within the context of a model with one and two types of charge carriers. It is established that, since x = 0.05, the TlIn_1–xYb_xTe₂ solid solutions belong to the class of narrow-gap semiconductors that have high matrix elements of interaction.

The effect of doping on the optical transmittance of germanium single crystals is studied by infrared Fourier spectroscopy. It is established that the introduction of silicon and tellurium additives into germanium doped with antimony provides a means for improving the temperature stability of the optical properties of the crystals.

The room-temperature generation of multiperiod quantum-cascade lasers (QCL) at a wavelength of 5.8 μm in the pulsed mode is demonstrated. The heterostructure of a quantum-cascade laser based on a heterojunction of InGaAs/InAlAs alloys is grown by molecular-beam epitaxy and incorporates 60 identical cascades. The threshold current density of the stripe laser 1.4 mm long and 22 μm wide is ~4.8 kA/cm² at a temperature of 303 K. The maximum power of the optical-radiation output from one QCL face, recorded by a detector, is 88 mW. The actual optical-power output from one QCL face is no less than 150 mW. The results obtained and possible ways of optimizing the structure of the developed quantum-cascade lasers are discussed.

For ZnO films, nanorods, and bulk single crystals doped with Er⁺ ions, it is shown that the effect of codopants introduced into the cation and ion sublattices and the observation of a high-intensity emission band at the wavelength λ_max = 1535 nm are defined by the local environment of the Er⁺ ion. Doping of the films and single crystals with Er⁺ ions by diffusion brings about an infrared (IR) emission band with a low intensity because of an inadequate concentration of impurity ions. The emission intensity of this band can be raised by introducing additional Ag, Au, or N⁺ impurities into the ZnO films. The UV-emission intensity of the Er-doped films and single crystals at λ_max = 368–372 nm is identical to that of the undoped films. ZnO nanorods doped with Er only or together with Al or Ga codopants exhibit only one IR band (at λ_max = 1535 nm), whose intensity decreases upon the introduction of codopants. Doping of the nanorods with the N⁺ gaseous impurity during growth (930 < T < 960°C) and then with the Er⁺ impurity by diffusion does not yield a substantial increase in the IR-emission intensity compared to the that of the corresponding band for nanorods not doped with the N⁺ impurity. In the Er-doped nanorods, whose photoluminescence spectra exhibit a high-intensity band at λ_max = 1535 nm, the UV emission band at λ_max = 372 nm is practically lacking.

For the anisotropic PbSb₂Te₄ single crystal with a high hole concentration (p ≈ 3 × 10²⁰ cm^–3) and high conductivity (σ ≈ 2500 Ω^–1 cm^–1), the reflectance spectrum for a cleavage plane orthogonal to the trigonal axis C₃ is recorded in a wide spectral range from 50 to 50000 cm^–1. It is shown that, in the long-wavelength and mid-infrared regions, the reflectance can be described with consideration for the contribution of plasma vibrations and two crystal-lattice vibrations. The quantitative characteristics of these vibrations are determined. The characteristics are in satisfactory agreement with the electrical parameters. The discrepancies between the values of the hole effective mass calculated by different methods are attributed to the complex structure of the crystal’s valence band.

Photoemission studies of the electronic structure of the Cs/nano-SiC/Si(111)-4° nanointerface are for the first time carried out with the use of synchrotron radiation in the photon energy range 120–450 eV. The in situ experiments are conducted in the case of submonolayer Cs coating of the surface of an epitaxial SiC layer grown on the vicinal surface Si(111)-4° by a new method of substrate-atom substitution. Modification of the valence-band spectra and the C 1s and Si 2p core levels is studied. The appearance of Cs-induced surface states, with binding energies of 1.2 and 7.4 eV, and a sharp change in the spectrum of the C 1s core level with the appearance of two additional modes are found. The evolution of the spectra shows that the Cs/nano-SiC/Si(111)-4° interface is formed due to charge transfer from Cs adatoms to surface atoms at terraces and steps of the vicinal surface. It is found that the structure of the C layer is nontrivial and involves energetically different carbon states.

Planar silicon nanostructures that are formed as a very narrow silicon quantum well confined by δ barriers heavily doped with boron are used to study the dielectric properties of DNA oligonucleotides deposited onto the surface of the nanostructures. The capacitance characteristics of the silicon nanostructures with oligonucleotides deposited onto their surface are determined by recording the local tunneling current–voltage characteristics by means of scanning tunneling microscopy. The results show the possibility of identifying the local dielectric properties of DNA oligonucleotide segments consisting of repeating G–C pairs. These properties apparently give grounds to correlate the segments with polymer molecules exhibiting the properties of multiferroics.

Photovoltaic converters of laser light with a wavelength of λ = 1550 nm are developed using liquidphase epitaxy (LPE), metal-organic chemical-vapor deposition (MOCVD), and diffusion from the gas phase into the n-GaSb substrate. Photocells with an area of S of 4, 12.2, and 100 mm² are fabricated and tested. The characteristics of the samples produced by different methods are compared. The monochromatic efficiency is found to be 38.7% for the best converters (with S = 12.2 mm²) at a laser power of 1.4 W.

A possible mechanism for natural-microplasma turn-off in silicon p–n junctions is studied. It is shown that the turn-off effect is not a random process, but is based on a certain physical mechanism. The mechanism is associated with the formation of graded-gap regions caused by thermoelastic stresses and electric- field redistribution in the microplasma region.

The power characteristics of quantum-well lasers with asymmetric barrier layers, which represent a novel type of injection laser, are calculated on the basis of an extended model taking into account asymmetry in the filling of electron and hole states. The electron–hole asymmetry is shown to have no significant effect on the characteristics of these lasers. Even in the presence of intermediate layers (located between the quantum well and each of the two asymmetric barrier layers), where parasitic electron–hole recombination does occur, the internal differential quantum efficiency of such a laser exhibits only a weak dependence on the pump current and remains close to unity; therefore, the light–current characteristic remains linear up to high pumping levels.

The Postgrowth processing of GaAs/AlGaAs multilayer heterostructures for terahertz quantumcascade lasers (QCLs) are studied. This procedure includes the thermocompression bonding of In–Au multilayer heterostructures with a doped n⁺-GaAs substrate, mechanical grinding, and selective wet etching of the substrate, and dry etching of QCL ridge mesastripes through a Ti/Au metallization mask 50 and 100 μm wide. Reactive-ion-etching modes with an inductively coupled plasma source in a BCl₃/Ar gas mixture are selected to obtain vertical walls of the QCL ridge mesastripes with minimum Ti/Au mask sputtering.

The polarization characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts and a rhomboidal oxide current aperture are studied. It is found that radiation polarization is always directed along the minor diagonal of the rhomboidal aperture (along the [\(\overline 1 \) 10] direction) for all single-mode VCSELs. The numerical simulation of carrier transport does not reveal the significant anisotropy of carrier injection to the active region. Furthermore, an analysis of the spatial distribution of the fundamental mode for two orthogonal polarizations within an effective waveguide model shows close transverse optical-confinement factors. Optical loss anisotropy in the asymmetric microcavity and/or gain anisotropy in the strained active region are the most likely mechanisms responsible for fixing the polarization.

A new method is used to raise the spectral sensitivity of photodiodes based on GaSb/GaInAsSb/GaAlAsSb heterostructures for the spectral range 1.1–2.4 μm. It is shown that, with a profile formed as pits on the metal-free unilluminated rear surface area of the photodiode chip, it is possible to improve the spectral sensitivity of the photodiodes at wavelengths in the range 1.8–2.4 μm. The most pronounced increase of up to 53% at the sensitivity maximum, compared with the sensitivity of conventional photodiodes with a fully metallized rear surface of the chip, is observed for photodiodes with shallow pits 30 μm in radius on their rear surface. These devices can find wide application in systems measuring the amount of water in petroleum products and the moisture content of paper, soil and grain.

The results of experimental studies of the gain properties of “thin” (3.2 nm thick) elastically strained InGaAs/InGaAlAs quantum wells emitting in the near-infrared spectral region near 1550 nm are presented. The results of studying the threshold and gain characteristics of stripe laser diodes with active regions based on “thin” quantum wells with a lattice–substrate mismatch of +1.0% show that the quantum wells under study exhibit a high modal gain of 11 cm^–1 and a low transparency current density of 46 A/cm² per quantum well.

The optimum mode of the in situ plasma-chemical etching of a Si₃N₄ passivating layer in C₃F₈/O₂ medium is chosen for the case of fabricating AlGaN/AlN/GaN НЕМТs. It is found that a bias of 40–50 V at a high-frequency electrode provides anisotropic etching of the insulator through a resist mask and introduces no appreciable radiation-induced defects upon overetching of the insulator films in the region of gate-metallization formation. To estimate the effect of in situ Si₃N₄ growth together with the heterostructure in one process on the AlGaN/AlN/GaN НЕМТ characteristics, transistors with gates without the insulator and with gates through Si₃N₄ slits are fabricated. The highest drain current of the AlGaN/AlN/GaN НЕМТ at 0 V at the gate is shown to be 1.5 times higher in the presence of Si₃N₄ than without it.