The electronic structure of chromite (FeCr
2
O
4
spinel) is described and the orbital ordering, band gap, and charge transfer are analyzed consistently in the framework of density functional theory ...taking into account strong electron correlations (DFT +
U
method). It is shown that the top of the chromite valence band in this model is formed by the ordered
t
2
g
orbitals of iron atoms located at tetrahedral sites, and the formation of hole polarons occurs involving just these orbitals. The nonadiabatic activation barrier determining the hole polaron transport is considered. The results of calculations of the band gap and activation energy are compared to the available experimental data.
A model is proposed that makes it possible to analytically analyze the speed performance of a waveguide
p
–
i
–
n
photodiode with a light-absorbing region representing a multilayered array of quantum ...dots separated by undoped spacers. It is shown that there is an optimal number of layers of quantum dots, as well as an optimal thickness of the spacers, which provide the widest bandwidth. The possibility of achieving a frequency range (at the level of –3 dB) above 20 GHz for waveguide photodiodes based on InGaAs/GaAs quantum well-dots is shown.
The Hall effect in single crystals of topological semimetals WTe
2
and MoTe
2
is studied in the temperature range from 2 to 100 K and in magnetic fields up to 9 T. It is established that the Hall ...resistivity of WTe
2
shows a nonlinear dependence on the magnetic field at temperatures below 100 K. At the same time, the Hall resistivity of MoTe
2
depends linearly on the magnetic field in the temperature range from 2 to 25 K and a nonlinear contribution appears at 50 K. Along with the known mechanism of compensation/decompensation of electron and hole charge carriers, the nonlinear dependence of the Hall resistivity of WTe
2
and MoTe
2
single crystals on the magnetic field is associated with the scattering of charge carriers on the surface.
Abstract
An article is devoted to the study of the strength properties of interlayer adhesion and determination of Young's modulus by the ball instrumental indentation method for samples, made of ...various plastics using additive technology under normal conditions. This production method is chosen as the most appropriate for creating lightly stressed parts of complex geometry (up to 30 MPa) in the shortest possible time. One of the possible options for such products is full-size centrifugal wheels layouts of low power gas turbine units (up to 250 kW) for testing them in model conditions. It will ensure the work of the material in the elastic zone. The samples are considered, obtained by FDM method from various polymers such as: acrylonitrile butadiene styrene thermoplastic resin (ABS+), acrylonitrile butadiene styrene thermoplastic resin with addition of carbon fibers (ABS Carbon), nylon with addition of carbon fibers (Nylon Super Carbon), polyethylene terephthalate glycol (PETG) and a compound based on polylactide (PLA HP). Plastics, made by this method, have anisotropic properties. Therefore, in this work, the strength characteristics of the test samples interlayer adhesion under tension are determined.
The static and dynamic characteristics of waveguide photodetectors with an absorbing region based on InGaAs/GaAs quantum well-dots were studied at room temperature. The absorption band of InGaAs/GaAs ...quantum well-dots is in the spectral range from 900 to 1100 nm. The waveguide photodetectors have a width of 50 μm and a length of the absorbing region from 92 μm to 400 μm. A low dark current density (1.1 and 22 μA/cm
2
at –1 and –20 V) and cut off frequency of 5.6 GHz, limited by the time constant of a parasitic equivalent electric
RC
-circuit, were obtained.
Abstract
In this paper, results are presented on III-V quantum well dot microring diode lasers tested at elevated temperatures. To the best of our knowledge, the first uncooled microdisk lasers with ...diameter of 40 μm with 3-dB bandwidth above 2 GHz at 55
°
C are demonstrated.
The temperature characteristics of ring lasers with a diameter of 480 μm of an original design with an active region based on 10 layers of InAs/InGaAs/GaAs quantum dots are studied. The lasers ...demonstrated a low threshold current density (200 A/cm
2
at 20°C), the characteristic temperature of the threshold current in the range of 20–100°C was 68 K, the maximum lasing temperature was as high as 130°C. These values are only slightly inferior to the parameters of the edge-emitting lasers fabricated from the same epitaxial wafer.
We studied a far-field emission pattern for microlasers with InGaAs/GaAs quantum well-dots in the active region. Angular-resolved electroluminescence spectra measurement revealed various far-field ...patterns depending on current and resonance mode.
The scanning interferometer method is used to measure the line width of microdisk and microring lasers with a diameter of the resonator ranging from 15 to 50 μm and active area based on InGaAs/GaAs ...quantum well-dots. Above the threshold, the spectral width of the line did not exceed 3 pm for all samples under study.
PDF
