III-N ring microlasers on a silicon substrate with InGaN/GaN active layers emitting near 420 nm were investigated. The growth conditions and fabrication steps were optimized to realize stable lasing under optical pumping in cavities with a diameter of 6-10 mu m. Chemically sensitive transmission electron microscopy images indicate that InGaN layers present in form of isolated islands. Between these InGaN islands, large areas of GaN are visible, forming barriers to lateral transport of free charge carriers in the active region and preventing their nonradiative surface recombination. For the first time, temperature stability of InGaN/GaN microring lasers characteristics are studied and lasing up to 100 degrees Celsius is demonstrated with the wavelength shift less than 1 nm. At room temperature, the threshold pump power is as low as 220 kW/cm(2). The obtained results significantly expand the potential areas of application of III-N microlasers.

We consider n-type gallium nitride crystals heavily doped with hydrogen-like donors (silicon or germanium atoms) and weakly to moderately compensated by hydrogen-like acceptors (magnesium atoms). Donor and acceptor concentrations correspond to the metallic side of the insulator-metal concentration phase transition (Mott transition). The shift of the conduction band (CB) electron mobility edge into the bandgap, caused by electrostatic fluctuations in the interaction energy between electrons and impurity ions, is taken into account. Within the relaxation time approximation for electron quasi-momentum, the dependences of stationary (DC) electrical resistivity and drift mobility on the concentration of CB electrons in n-GaN crystals are calculated. Each act of elastic Coulomb scattering of a CB electron by a donor or acceptor ion is assumed to occur within a spherical volume of the crystal matrix associated with a single ion. Electron scattering on phonons is considered according to Matthiessen's rule. The calculation results, obtained using the proposed formulas without fitting parameters, quantitatively agree with experimental data over a wide range of CB electron concentrations. From analysis of experimental data, a new approximation formula for drift mobility at room temperature is obtained. The results using the new approximation and the proposed theoretical formula are consistent.

Lasing under pulsed optical pumping for AlGaN/AlGaN whispering gallery mode microlasers on sapphire is demonstrated in the temperature range of 20-195 degrees C. The lasers diameter ranges from 2 to 4 mu m. The lasing wavelength is about 255 nm at room temperature with the temperature-induced shift as small as 0.043 nm/K highlighting the potential of these devices for compact UV-C photonic applications.

Technological progress makes it possible to significantly reduce the size of semiconductor laser emitters to microscales and sizes commensurate with the emission wavelength. Extreme laser miniaturization can be achieved using disk or ring resonators supporting high-Q whispering gallery modes (WGM). WGM lasers are interesting not only due to small sizes (small mode volume) but also for their long times of light-matter interaction, unique capabilities of sensing and studying of quantum chaos and so on. On the other hand, small losses for the output of emission in high-Q resonators can negate the practical benefits of the laser or even completely hide the peculiarities of the light physics inside the cavity. In this review, we attempted to summarize the published data on the achieved optical output power in different III-V injection microlasers and analyzed the key characteristics that limit the maximum output power, especially influence of the active region self-heating at cw operation and impeded light extraction out of WGM cavities. We compared various III-V materials and fabrication methods developed for improving emission output. We also observe very low relative intensity noise in microdisk lasers and harmonics of the resonance frequency in the relative intensity noise spectrum.

In this paper, CaGa2S4:3%Nd,5%Yb; CaGa2S4:5%Yb; CaGa2S4:3%Nd compounds were synthesized, and their photoluminescence (PL) spectra, PL excitation (PLE) spectra and PL decay properties were studied at room temperature under one-photon and multi-photon excitation in a wide range of excitation intensities. The synthesis of the CaGa2S4 compound was carried out by a solid-phase reaction of a stoichiometric mixture of CaS and Ga2S3 powders in a quartz ampoule. Yb and Nd doping was carried out during the synthesis process using YbF3 and NdF3. PLE spectra were studied in the wavelength range from 250 to 850 nm, and PL spectra in the range of 400-1500 nm. It has been shown that after introducing Yb3+ ions into thiogallate crystals with Nd3+ ions, a new band near 488 nm is formed and the PL intensity increases by 1-2 orders of magnitude. The anti-Stokes PL spectra of CaGa2S4: Nd, Yb crystals in the visible region of the spectrum (400-700 nm) were studied when excited by continuous wave laser radiation with a wavelength of 975 nm. The kinetics of PL decay of all types of compounds at different wavelengths of single- and multi-photon excitation were determined. Depending on the PLE conditions, wavelength and intensity of the exciting radiation, monoexponential and non-monoexponential decay kinetics were observed with decay times in the range of 20-90 mu s. Possible mechanisms of PLE and PL of CaGa2S4 crystals doped with neodymium and ytterbium ions are discussed.

The aim of the work was to study the structure and defects of a channel transistor with two types of conductivity (p and n), the submicrostructures based on nickel silicide films, and the seed layers based on AlN using atomic force microscopy (including conductive or electric force method, which allow one to study the electrical conductivity of the material surface). The influence of the manufacturing technology and local oxide formation on the relief and structure of the pand n-type transistor was established. The local oxide is necessary for the electrical isolation of the transistors from each other. The surface roughness is higher on the surface and outside the p-channel transistor than on the n-channel transistor. When examining the AlN layers both in the topography mode and in the adhesion mode, defects in the form of pores were revealed, which are places of electrical breakdowns, which worsens the properties of the such heterostructures. With an increase in the temperature and time of nitriding, the defects of the AlN layers significantly decrease. The conductive areas on the surface of the nickel silicides after rapid thermal treatment at 300 and 400 °C using electric force microscopy were detected, which shows incomplete formation of nickel silicide during the treatment. Thus, the efficiency of the atomic force microscopy method using a specialized conductive technique as a method for monitoring microelectronic components was demonstrated.

An application of compact benchtop X-ray diffractometer for investigation of thin film semiconductor structures was demonstrated. A depth-dependent qualitative phase analysis of multilayer polycrystalline CuInGaSe2-based solar cell structure was performed. The independent goniometer allowed determination of residual stress values in the molybdenum layer of the solar cell. Grazing-incidence X-ray diffractometry was used to estimate polycrystallinity degree of AlN layers grown by molecular beam epitaxy and correlate it with the growth temperature. X-ray reflectometry measurement were also performed for nucleation AlN layer.

A study was carried out on the luminescence excitation spectra and photoluminescence (PL) spectra as well as the luminescence kinetics of low-density polyethylene composites with different contents of CaGa2S4:Eu2+ phosphor filler. The phospholuminescence was attributed to the 4f65d → 4f7 transition of the Eu3+ ion and was greatest when the filler concentration was 7 vol.

The effect of irradiation with different doses of 4-MeV electrons on radiative recombination of nonequilibrium charge carriers in Cu(In,Ga)(S,Se)2 thin films of solar cells was studied. Near-edge photoluminescence (PL) in the energy range 0.9–1.2 eV in nonirradiated and irradiated direct-gap Cu(In,Ga)(S,Se)2 solid solutions was caused by optical interband transitions and radiative recombination through energy levels of acceptor- and donor-type structure defects in the presence of strong potential fluctuations. PL spectra measured in the temperature range 5–300 K exhibited energy shifts of the near-edge PL band maxima and redistributions of their intensities in thin films after irradiation with different doses of electrons. The activation energies of nonradiative recombination were determined from the quenching of PL band intensities. The possible nature of structural defects in nonirradiated and electron-irradiated Cu(In,Ga)(S,Se)2 solid solutions was discussed.

Dependences of the morphology and optical properties of silicon nanostructures on the laser ablation synthesis conditions, namely, the laser focusing conditions, laser pulse repetition rate, and temperature and composition of the solution, were established. The obtained regularities were used to develop a method for formation of Si–Ag and Si–Ag–Cu hybrid metal–silicon nanostructures. The obtained broadband absorption of the Si–Ag–Cu nanoparticles is promising for application in nanofluids for photothermal energy conversion of solar radiation.

Al x Ga1−x N layers (x = 0.6−0.75) grown using plasma‐assisted molecular beam epitaxy with alternating metal‐enriched stoichiometric conditions using an off‐centered nitrogen flux demonstrate sharp compositional modulation with the formation of monolayer (ML)‐thick Ga‐enriched quantum disks embedded in a Ga‐depleted AlGaN matrix. These structures have a constant modulation period of ≈3 ML over the entire surface of a 2‐inch substrate, and the modulation amplitude increases from zero to maximum with distance from the center of the substrate. This is confirmed experimentally by conventional and scanning transmission electron microscopes, as well as studies of optical absorption and photoluminescence (PL) mappings. The PL measurements also show a high efficiency of ultraviolet‐C (UVC) radiative recombination at room temperature in these layers with an atomically smooth surface topology, emitting in the spectral range 250–290 nm with the maximum ratio of PL intensities measured at high (310 K) and low(10 K) temperatures up to 58%. Moreover, these layers demonstrate stimulated emission with the lowest threshold optical power density of 240 kW·cm−2 (at 287 nm) for the Al0.6Ga0.4N layer with the highest degree of compositional modulation. The results obtained can be used to develop technologies for growing ML‐scale heterostructures in (Al,Ga)N material system.

A compact reference UVC source based on commercially available LED has been developed. The article presents the design and results of the study of the optical characteristics of the radiation of the reference UVC LED source. The source provides a power density of radiation up to 400 μW/cm 2 on area of 3×3 mm with inhomogeneity of 1.5 %.The emission band of a source with a maximum of 265 nm is predominantly 97 % in the UV-C spectrum region, and a small part of it is inUV-B and UV-A regions, 2.7 % and 0.3 %, respectively. The use of ComboSource for laser diodes allowed to precisionally stabilize the injection current and temperature of the LED. It is shown that overheating of the active region of the selected UV LED is only 10°C - 25°C at the recommended injection currents due to the peculiarities of its design. This results in a low degradation rate of the UV LED. Possible ways to improve the characteristics of the reference UVCsource are discussed.

The capabilities of liquid-assisted laser ablation technique with additional laser irradiation of solutions for the synthesis of SiC nanocrystals (NCs) have been investigated. Nanocrystalline particles of silicon carbide were synthesized by laser irradiation of the mixture of Si and C colloidal solutions using nanosecond and femtosecond laser radiation. For optimization of the conditions for the binary nanoparticles (NPs) formation, the characterization of inner structure, phase composition and morphology was performed by means of high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), X-ray photoelectron (XPS), Raman and Fourier-transform infrared (FTIR) spectroscopy and correlation of NPs properties with laser irradiation conditions were found. The characterization results proved the formation of near-spherical SiC NCs which exhibited photoluminescence (PL) in the broad spectral region of 350–600 nm. The origin of the observed photoluminescence is attributed to quantum confinement in small NCs, radiative recombination of photogenerated charge carriers, surface defects or silicon oxycarbide phases. The developed simple approach enables synthesis of colloidal SiC NPs that potentially satisfy the requirements of good dispersibility, stability and efficient PL for applications in biological labeling.

Представлены результаты исследования спектров излучения кристаллов и тонких пленок CuInSe 2 при непрерывном (2 Вт/см 2 ) и наносекундном импульсном лазерном возбуждении в диапазоне плотности мощности возбуждения ~1–100 кВт/см 2 и температурах 10–160 К. Обнаружено, что в кристаллах CuInSe 2 стимулированное излучение возникает в спектральной области 1,033 эВ с минимальным уровнем пороговой накачки 9,8 кВт/см 2 , а при уровнях накачки 36–76 кВт/см 2 наблюдается лазерное излучение. Установлено, что для тонких пленок CuInSe 2 , сформированных на стеклянных подложках с предварительно осажденным на стекло слоем молибдена (структура CuInSe 2 /Mo/стекло), характерно появление только стимулированного излучения в области энергий 1,014–1,097 эВ с минимальным уровнем пороговой накачки 30 кВт/см 2 при температуре 10 К. Обсуждаются механизмы возникновения стимулированного и лазерного излучения в соединении CuInSe 2 .

We investigated the radiative properties of InGaN/GaN heterostructures with multiple quantum wells (MQWs) grown on silicon substrates with different thicknesses of quantum wells at optical excitation. The correlation of laser and photoluminescent properties with the surface morphology of the gallium nitride coating layers and the density of V-defects has been established. It is shown that, with a growth in the density of V-defects, the threshold power density of the excitation of the generation of InGaN/GaN heterostructures with MQWs increases.

The photoluminescence (PL) of CaGa2S4:Pr3+ chalcogenide semiconductor compound is studied. The PL spectrum consists of a set of intense sharp lines at 494, 631, 654, and 741 nm, formed by intra-4f transitions of Pr3+ ions. The energy level diagram of CaGa2S4:Pr3+ is proposed. A broad structural band in the PL excitation spectra in the range of 270–360 nm is assumed with superposition of host related and 4f2 → 4f15d1 direct excitation transition bands whereas a sharp line at 456 nm—with 3H4 → 3P2 direct excitation. The PL decays at intensive emission lines at room temperature were found to obey nonexponential law with time constant in the range of 1.1–2.1 μs for fast decay component and of 4.5–6.3 ms for slow one. Thermal quenching by only 50% and 75% of the PL intensity of CaGa2S4:Pr3+ with 7 and 3 at. % Pr3+ ions concentration, respectively, was obtained in the range of 10–300 K. Extreme stability of PL spectra and efficiency of CaGa2S4:Pr3+ compound up to 105 W/cm2 of excitation power density was achieved.

Spontaneous and stimulated emission (SE) of thin Cu(In,Ga)Se 2 films, deposited on sodium-containing glass substrates and irradiated by protons with an energy of 2.5 keV and doses of 10 14 –10 17 cm –2 , were investigated upon excitation by nanosecond laser pulses with the power density from 5 to 100 kW/cm 2 . An increase in the intensity and a decrease in the SE appearance threshold were found for the films irradiated by protons with doses of 10 14 –10 15 cm –2 , in comparison with nonirradiated films. An increase in the SE threshold and a decrease in the intensity of SE and spontaneous emission were observed at the irradiation dose of 10 16 cm –2 . After a dose of 10 17 cm –2 the intensity of emission decreased sharply and the SE threshold was not reached. Possible reasons of the observed effects are discussed.

The influence of dislocations on luminescence of InGaN/GaN multiple quantum wells was investigated by temperature-dependent and time-resolved room-temperature photoluminescence measurements and analyzed via localized-state ensemble model. The results show that dislocations decrease non-radiative recombination time and do not affect either radiative recombination time or non-radiative recombination mechanism. Moreover, dislocation-related broadening, increasing linearly with increased dislocation density, was found to take place. However, a significant part of spectral width (∼55 meV) is not defined by either dislocation-induced or alloy- and thermally-induced broadening, revealing the existence of other broadening mechanisms (e.g. carrier–carrier scattering-induced broadening).

The structure and strength properties of vacuum aluminum condensates alloyed with iron in the concentration range of 0.1 – 3.2 at. % is studied in the paper. It is shown that up to a concentration of about 2 at. % Fe, the grain size decreases, the strength properties increase and the lattice parameter values of these objects remain unchanged. It is found that at an iron concentration of up to ~ 2 at. % its atoms are concentrated in the grain boundaries of the aluminum matrix metal in the form of grain boundary segregation. At high concentrations, the structure of condensates is a supersaturated solution of iron in the FCC crystal lattice of aluminum. Highly dispersed Al13Fe4 intermetallic compounds are present at the grain boundaries and within the volume of grains. It has been found that the Hall-Petch coefficient for one-component aluminum condensates is 0.04 MPa·m1/2, which is typical for this metal. For Al-Fe condensates, a positive deviation from the Hall-Petch dependence is observed and the coefficient k increases to 0.4 MPa·m1/2 for a structure with grain boundary segregations and to 0.14 MPa·m1/2 for condensates containing intermetallic compounds. The obtained experimental results are explained by the different structural-phase state of the grain boundaries of the aluminum matrix.

Excitonic quality CuInSe 2 crystals were studied using low-temperature (10 K) photoluminescence (PL) excited by continuous wave and nano-second pulsed lasers at power densities from 0.01 to 76kW/cm 2 . Increasing the excitation power density level to 26 kW/cm 2 resulted in the appearance of a stimulated emission SE-band in the PL spectra at 1.035eV. Further increase in the excitation level to 39kW/cm 2 generated on the top of the SE band, a structure of equidistant sharp lines attributed to laser emission.