Using electrons with energy about 15 keV, electron source based on a ferroelectric cathode and GaN/AIN MQW Structures the following values of power of UV-pulse radiation were obtained: $50 \mathrm{~W}(\lambda=240 \mathrm{~nm}, J=2240 \mathrm{~mA}), 69 \mathrm{~W}$ $(\lambda=248 \mathrm{~nm}, J=2500 \mathrm{~mA}), 71 W(\lambda=267 \mathrm{~nm}, J=2340 \mathrm{~mA})$

The paper reports on heterostructures for mid-ultraviolet (UVC) emitters with multiple (up to 400 periods) and single two-dimensional (2D)-GaN/AlN quantum disks/quantum wells with a nominal thickness below the critical thickness of ~2 monolayers (MLs) characterizing the transition of the 2D growth mode to 3D.The structures were grown by plasma-assisted molecular beam epitaxy (PA MBE) using low growth temperatures (~690C) in a wide range of gallium and activated nitrogen flux ratios Ga/N2* = 0.6  2.2 on various AlN/csapphire templates fabricated either by PA MBE or MOCVD.This made it possible to vary the surface topography from a 3D type under nitrogen-rich conditions to various types of 2D topographies in the structures grown under metal(Ga)-rich conditions.The absence of a Stranski-Krastanov transition in the latter structures was confirmed by a streaky RHEED pattern throughout the growth of QWs and barrier layers.The growth runs were monitored also by multi-beam optical stress sensor, which revealed an unusual stress relaxation in the ML-thick GaN/AlN heterostructures.Structural properties of GaN/AlN heterostructures were studied using X-ray diffraction analysis, including measurement of X-ray reflectance curves, atomic force microscopy, and high-resolution transmission microscopy.The results of these studies, together with the measurements of photoluminescence spectra, both cw and time-resolved, made it possible to suggest the formation of twodimensional GaN quantum disks with a thickness of either 1 or 2 ML and different lateral sizes on the stepped surface of the AlN barrier layers, which can lead to effective carrier localization.Moreover, we demonstrate a unique functional property of these atomically thin QW to maintain stable excitons, resulting in a particularly high radiation yield at room temperature.As a result, the emission energy (wavelength) from GaN/AlN 400QW structures could be varied from 5.21 eV (238 nm) to 4.68 eV (265 nm) and was connected with a simultaneous increased of charge carrier localization.Using electron-beam pumping with a plasma cathode ferroelectric electron gun ensuring a maximum pulse current of 2 A at an electron energy of 12.5 keV, a maximum output optical power of 50 W was achieved for the 265 nm structure, while the structure emitting at 238 nm demonstrated a power of 10 W, as shown in Fig. 1.In addition, we discussed the optical properties of cylindrical nanorods with diameters from 50 to 5000 nm, fabricated by the topdown technology from ML-thick GaN/AlN single QWs using a combination of wet and reactive ion etching.Photoluminescence measurements in an ultra-small QW region enclosed in a nanorod revealed narrow lines of individual excitons localized on potential fluctuations attributed to GaN quantum nano-disks 2-3 MLs high, which appear in a QW with an nominal thickness of 1.5 ML.A model that takes into account dark and bright exciton states was used to explain the features in the PL spectra, including their behavior with increasing temperature.This research was funded by

The parameters of radiation of fluorite CaF2 pumped by pulsed electron beam are presented. UV radiation at a wavelength of 300 nm, a pulse power of up to 1W at an electron energy of 39 keV, a beam current of 60 mA with a pulse duration of about 200 ns have been obtained. It is shown that the output radiation power is independent of temperature in the range of 25-100 ° C.

We report the results of a study of an e-beam pumped vertical-external-cavity surface-emitting laser (VECSEL) based on an InGaAs/AlGaAs heterostructure. Metalorganic chemical vapour deposition (MOCVD) is employed to grow two structures of different design, which contain 10 quantum wells (QWs) and a built-in distributed Bragg reflector (DBR) mirror. Under repetitively pulsed electron-beam excitation (50 Hz, 250 ns), a peak output power of 5.5 W is achieved at a wavelength of 2.5 W and an output power of 2.5 W at 1.013 mm with a total convergence angle no larger than 20 mrad.

During the operation of lasers based on an AlGaN/InGaN/GaN structure with electron-beam- and optical pumping, a gradual decrease in the output power is observed. In the first minutes of the operation of optical pumping lasers, a certain increase (by 5–10%) in the output power with a successive gradual decrease can be observed. Upon sample cooling, the rate of output-power degradation decreases. A decrease in the output power during operation of the laser is accompanied by changes in the emission spectrum—the line maximum shifts to the short-wavelength region and additional maxima appear. The observed effects can be explained both by the passivation of the initial defects and the diffusion of atoms of the structure during laser operation. The changes in the emission spectra are apparently associated with competition between two different generation channels.

Parameters of pulsed electron-beam and optically pumped lasers based on ZnCdSe/ZnMgSSe structures with a 2-μm-wide waveguide and an active region shifted towards the structure surface have been studied. It is shown that lasing occurs at the 3rd transverse mode of the optical cavity and the maximum output power could be increased essentially due to the decrease of the optical load on the laser mirrors.

ZnSe-based laser array pumped by a pulsed electron beam with an energy of 5.6 keV has been studied. Output pulse power up to 180 W per one facet at wavelength of about 548 nm was measured at room-temperature.

Ultimate Parameters of infrared, visible and blue-violet electron-beam-pumped lasers and laser arrays based on II-VI, III-V and III-N semiconductor heterostructures, obtained at electron energy below ~10keV are discussed.

The properties of an electron-beam-pumped ZnSe-based laser array consisting of 6 one-dimensional arrays, each comprising 10 single laser elements, have been studied. The peak output power up to 80-100 W at room temperature in "true" green (lambda=547 nm) spectral range has been demonstrated by using for pumping electrons with the accelerating energy as low as 5.6 keV. (C) 2016 WILEY-VCH Verlag GmbH & Co.

The parameters of pulsed blue-violet (lambda approximate to 430 nm at T = 300 K) lasers based on an AlGaN/InGaN/GaN structure with five InGaN quantum wells and transverse electron-beam pumping are studied. At room temperature of the active element, the minimum electron energy was 9 keV and the minimum threshold electron beam current density was 8 A cm(-2) at an electron energy of 18 keV.

The paper presents basic approaches in designing and growing by molecular beam epitaxy of (Zn,Mg)(S,Se)-based laser heterostructures with multiple CdSe quantum dot (QD) sheets or ZnCdSe quantum wells (QW). The method of calculation of compensating short-period ZnSSe/ZnSe superlattices (SLs) in both active and waveguide regions of laser heterostructures possessing the different waveguide thickness and different number of active regions is presented. The method allowing reduction of the density of nonequilibrium point defects in the active region of the II–VI laser structures has been proposed. It utilizes the migration enhanced epitaxy mode in growing the ZnSe QW confining the CdSe QD sheet. The threshold power density as low as P thr ∼ 0.8 kW/cm2 at T = 300 K has been demonstrated for laser heterostructure with single CdSe QD sheet and asymmetric graded-index waveguide with strain-compensating SLs.

The parameters of electron beam pumped RT lasers based on ZnSe-containing MQW structures were studied. Maximum value of output pulse power as high as 82W per laser facet has been demonstrated. Both the high value of Pmax and the threshold of catastrophic degradation in comparison with the earlier results could be explained by the relatively low level of defect density (~104 cm-2) in the laser structure.

It has been demonstrated that after 3 - 5 minutes irradiation of the MBE grown ZnSe-based electron beam pumped laser heterostructures with the light intensity of mercury lamp of 40-60 W/cm2, the luminescence intensity increased by ~20-50 %, whereas the threshold current density reduced by 20-40 %. Evidently, the results could be explained by the annealing (or optical transformation) the initial point defects in the active area of the laser heterostructure induced by low-temperature growth.

Catastrophic degradation of pulsed lasers based on InGaAs/AlGaAs/GaAs structures with different design of the active domain with transverse pumping by the electron beam at T = 300 K is studied. In lasers based on structures with a InGaAs single quantum well and with seven quantum wells, the maximal values of pulsed power are 70–90 and 10–20 W, respectively.

Исследованы характеристики сканирующего импульсного лазера зеленого диапазона на основе ZnSe-содержащих структур с накачкой электронным пучком длительностью 200 нс с энергией 8 кэВ. При комнатной температуре активного элемента при частоте сканирования 20 Гц и частоте следования импульсов 3 кГц средняя мощность излучения составила 1.6 мВт при импульсной мощности 2.7 Вт.

Temperature dependence of threshold current density in the range 50-300 K for lasers based on InGaAs/AlGaAs/GaAs quantum-dimensional heterostructures under electron beam pumping with electron energy in the range 2-11 keV is investigated. Minimal threshold current density value as low as 0.05 A/cm2 at the electron energy of 9-11 keV and temperature 200 K is obtained. Laser generation is obtained at record low electron energies: less than 2.5 keV at T<;150 K and 3.5 keV at T=300 K. The possibility of further reducing of electron energy at T=300 K is discussed.

The gradual degradation of green-range pulse lasers based on ZnSe-containing quantum-well structures with optical and electron-beam pumping has been investigated. The operation of the lasers over several hours without decreasing the output power (with the active elements at room temperature and a pulse repetition rate of 50 Hz) has been shown.