Vol 55, No 5 (2019)

Ge layers heavily doped by a donor impurity are formed by implanting a p-Ge single crystal by two-charge antimony ions (Sb⁺⁺) with the energy E = 80 keV and the dose Φ = 10¹⁶ cm⁻² with subsequent pulsed annealing of the implanted Ge:Sb layer by powerful ion beams (C⁺, H⁺) of nanosecond duration in a liquid phase regime. The surface morphology and depth profiles of Sb, the crystalline structure of the layer, the concentration of electrically active atoms, and photoluminescence of the Ge:Sb layers are investigated. The data on the Sb depth distribution are compared with the computer simulation results and show good agreement. The obtained results indicate that a high degree of activation of the implanted Sb (up to 100%) and an increase in the direct-gap photoluminescence in the heavily doped layer for 300 K with a peak at 0.77 eV.

Two types of mirror structures with saturable absorption are under consideration: monolithic mirrors grown from semiconductor materials and mirrors with a dielectric reflector, with quantum well containing semiconductor structures transferred to the dielectric. Both types of mirrors manifest high reflectivity in the NIR range of the spectrum: the table width is about 100 nm for semiconductor reflectors and more than 200 nm for dielectric reflectors. It is shown that a maximum depth of absorption modulation from 1 to 40% is possible. The recovery time of the saturable absorber (2 ps) makes these mirrors significantly fit for using in lasers with a pulse repetition rate of 1 GHz.

This paper presents the results of numerical simulation for \(\bar 43m\) crystals and experimental results for azimuthal angular dependences of polarization components of a second harmonic signal reflected from GaAs(013) substrates, CdTe/ZnTe/GaAs buffer layers, and Cd_xHg_1−xTe/CdTe/ZnTe/GaAs structures, sequentially grown on these substrates with normal incidence of probing laser radiation on the sample and azimuthal rotation of its polarization plane. It is revealed from investigating the GaAs(013) substrates and CdTe/ZnTe/GaAs buffer layers that deviations from the base cut (013) relative to angles θ and ϕ turn out to be 1–3° in the GaAs substrates and up to 8° in the CdTe/ZnTe/GaAs buffer layers. The observed asymmetry of the minima of angular experimental dependences of the second harmonic signal in the GaAs substrates is related to stresses. It is assumed on the basis of the experimental data that the values of the components of the nonlinear susceptibility tensor χ_xyz(ω) of the crystalline structure Cd_xHg_1−xTe significantly exceed those of similar tensor components in CdTe and GaAs.

Waveguide microstructures based on strained silicon with the use of silicon carbonitride and silicon nitride films as cladding layers are created. A plasma-enhanced chemical vapor deposition technique is developed, which allows obtaining high values of intrinsic mechanical stresses in films (about 700 MPa). The strained waveguide structures are characterized by micro-Raman spectroscopy during a scanning procedure. It is demonstrated that deposition of silicon carbonitride and silicon nitride films induces compressive stresses in the silicon waveguide, which is proved by the shift of the maximum of the main peak of scattering on LO-phonons of silicon toward higher wave numbers. The compressive stresses in the silicon waveguide clad with silicon nitride and carbonitride layers are estimated as 350 and 250 MPa, respectively, which is sufficient for the emergence of nonlinear optical properties of silicon (Pockels effect).

Terahertz emission spectra of the surface of silicon crystals with different types of conductivity were experimentally recorded upon excitation by femtosecond laser pulses at various temperatures. The observed features in the terahertz spectra of the silicon surface correspond to the energy structure of the impurity centers determining the type of conductivity of the sample. Comparison was made with the results obtained in the case of deposition of gold nanoparticles on a semiconductor surface. The spectral features of the surface with deposited nanoparticles are discussed using the terahertz re-emission mechanism in two-phonon absorption.

The theory of coherent photon-assisted electron transmission through a one-dimensional smooth barrier is successfully used to model the results of measuring the terahertz photoconductivity of a tunneling point contact in a two-dimensional electron gas. For this barrier in a deeper tunneling mode, photon steps in the curve of the transmission coefficient versus initial electron energy were found. Their position is determined by the terahertz photon energy.

A method is proposed for determining the orientation of phospholipid molecules in planar structures from spectra of non-polarized Raman scattering. The method is based on the sensitivity of the intensity of lines of Raman scattering from vibrations of CH₂ groups to the orientation of phospholipid molecules. The validity of the method is illustrated on a planar sample of a saturated phospholipid prepared by drying from a solution. The principal component analysis is demonstrated to be a convenient tool for analyzing the spatial distribution of molecule orientations in the sample.

The absorption spectral characteristics of silicon dioxide films in the IR range (λ = 8–14 µm) were studied to determine the optimal absorber thickness in the matrix structure of Golay microcells in order to design highly sensitive IR detectors. It is shown that the absorbance spectrum of SiO₂ films deposited by electron-beam evaporation has a multipeak structure in the thickness range up to 2 µm and differs from the known absorption spectra of bulk silicon dioxide, which is apparently due to rearrangements in the film stoichiometry at the initial stages of film formation. Experiments have shown that the integrated absorption in deposited films in a given spectral range is close to a linear dependence on thickness and an order of magnitude smaller than the value obtained by calculation based on literature data for bulk SiO₂.

Diffusion of charge carriers in the photosensitive film of infrared mercury—cadmium—tellurium (MCT) focal plane arrays (FPAs) is simulated by the Monte Carlo method for determining the spatial resolution of these FPAs. Calculation results for matrix and linear FPAs with variously designed FPA pixels, including configurations with isolating diodes, are reported. The calculated data are compared with the experimentally measured resolution values of real FPAs.