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Pulsed radiative characteristics of high-power semiconductor lasers based on an asymmetric InGaAs/AlGaAs/GaAs heterostructure with an active region including two quantum wells and a gradient waveguide on the side of the p-emitter are studied. It is shown that the use of the proposed design allows efficient laser operation under pumping by 100-ns current pulses in the temperature range 25 – 90 °C. The lasers with a Fabry – Perot cavity 2900 μm long demonstrated peak powers of 62 W (injection current 123 A) and 43 W (122 A) at temperatures of 25 and 90 °C, respectively. It is found that at room temperature and currents of ∼50A, a decrease in the cavity length to 600 μm does not cause a decrease in the output power with respect to the power of lasers with a long (2900 μm) cavity. An increase in temperature to 90 °C at high injection currents leads to a sharp decrease in the radiative efficiency of lasers with a short (600 μm) cavity and to the change of their operation regime to the two-band lasing.

Longitudinal spatial hole burning (LSHB) in high-power semiconductor lasers is analysed by numerically solving one-dimensional (1D) rate equations. Calculations are performed for GaAs-based lasers operating at a wavelength of 1.06 μm. It is shown that the LSHB-induced decrease in output power can be accounted for by two mechanisms: build-up of spontaneous recombination and decrease in slope efficiency, equivalent to a rise in internal optical loss. We analyse the influence of different laser chip parameters on the magnitude of the LSHB effect. In particular, it is shown that to suppress LSHB it is preferable to increase the optical confinement factor Γ. We examine the relationship between LSHB and other mechanisms capable of reducing the output power.

Forster resonance energy transfer in inhomogeneous dense arrays of epitaxial CdSe/ZnSe quantum dots is demonstrated by time- and space-resolved photoluminescence spectroscopy. The specific feature of this process is the dipole–dipole interaction between the ground exciton levels of small quantum dots and the excited levels of large dots. This interaction brings efficient energy collection and spectral selection of a limited number of emitters. Results of theoretical modeling of optical transitions in spheroidal quantum dots with a Gaussian potential profile agree with the observed features of optical spectra induced by the change of the dominant energy transfer mechanism.

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.

A significant (by up to a factor of 7) increase in the internal quantum efficiency of luminescence is achieved at room temperature in semiconductor-metal-insulator hybrid structures fabricated by the successive deposition of gold and Si3N4 over an array of InGaN nanoblocks, grown by molecular-beam epitaxy. The observed effect can be accounted for by the resonant interaction of excitons localized in InGaN nanoblocks with localized surface-plasmon modes in gold intrusions embedded into InGaN and Si3N4.

Small-signal-controlled optical modulator structure capable of operation at several wavelengths is suggested. It is shown that the application of spectrally selective mirrors makes it possible to develop optically integrated cavities that provide lasing at prescribed discrete wavelengths and a control section that can vary the internal optical loss. The main relationships between the lasing-mode switching conditions and optical-modulator structure parameters are determined. Optical modulators for the 1060–1080 nm spectral range, with a distributed Bragg reflector as one of the mirrors, are developed and experimentally investigated. It is shown that small-signal control by a forward current can switch the lasing between optically integrated Fabry-Perot cavities at a 5–20 ns rate.

The electrophysical properties of InSb/AlInSb/AlSb heterostructures with a high electron concentration are reported. We have observed anisotropy of the electron concentration and mobility measured at a low magnetic field in the [110] and \(\left[ {1\bar 10} \right]\) crystallographic directions. It has been established by analysis of Shubnikov-de Haas oscillations that the conductivity through the two-dimensional electron channel InSb/AlInSb quantum well (QW) does not depend on the crystallographic direction. However, the magnetic-field dependences of the Hall coefficient and resistivity of the structures reveal a strong influence of the crystallographic directions. This has allowed one to conclude that the anisotropy of the electron transport parameters in the QW structures measured at low magnetic fields correspond to parasitic conductivity through the Al0.09In0.91Sb buffer layer with two pronounced anisotropic contributions: the influence of metallic In nanoclusters inhomogeneously distributed within the buffer layer and conductivity of the near-interface layer with a high anisotropic density of extended defects.

We report on the unusually large blue shift of the electroluminescence spectrum with an increase of the drive current at 77 K in a double-barrier nanoheterostructure with a deep AlSb/InAs0.83Sb0.17/AlSb quantum well grown by metal-organic vapor phase epitaxy on the n-GaSb:Te substrate. The rise of the drive current from 20 mA to 220 mA led to a shift of the electroluminescence spectrum maximum toward higher photon energies by 100 meV. It was shown that this effect is due to indirect (tunneling) radiative transitions between electrons in InAsSb quantum well and heavy holes localized near the AlSb/p-GaSb heterointerface. The energy of radiative transition was linearly dependent on the applied voltage. In the drive current range of 50–220 mA, an electroluminescence blue shift was accompanied by spectrum narrowing by 40 meV and a noticeable change of the spectrum shape. With a rise in the drive current, a superlinear increase of the electroluminescence intensity caused by the nonlinear dependence of tunneling radiative recombination rate on transition energy was observed at 300 K and 77 K.We report on the unusually large blue shift of the electroluminescence spectrum with an increase of the drive current at 77 K in a double-barrier nanoheterostructure with a deep AlSb/InAs0.83Sb0.17/AlSb quantum well grown by metal-organic vapor phase epitaxy on the n-GaSb:Te substrate. The rise of the drive current from 20 mA to 220 mA led to a shift of the electroluminescence spectrum maximum toward higher photon energies by 100 meV. It was shown that this effect is due to indirect (tunneling) radiative transitions between electrons in InAsSb quantum well and heavy holes localized near the AlSb/p-GaSb heterointerface. The energy of radiative transition was linearly dependent on the applied voltage. In the drive current range of 50–220 mA, an electroluminescence blue shift was accompanied by spectrum narrowing by 40 meV and a noticeable change of the spectrum shape. With a rise in the drive current, a superlinear increase of the electroluminescence intensity caused by the nonlinear dependence of tunneling...

A method for the fabrication of 2D periodic structures by contact optical photolithography with image inversion is reported. The optical properties of photonic crystals and Bragg gratings for mid-IR and terahertz emitters are considered. The possibility of raising the integral emission intensity of light-emitting diodes for the mid-IR spectral range is demonstrated. The requirements to gratings for the output of terahertz emission generated by surface plasmons excited in layers of narrow-gap degenerate semiconductors with an accumulation layer are determined.

Approaches to the development of laser heterostructures with a broadened single-mode waveguide are studied theoretically and experimentally. It is shown that the use of n- and p-type emitters with different refractive-index values ensures lasing in the fundamental mode only, if the thickness of the waveguide layer is 2 μm. The studied semiconductor lasers fabricated using the developed heterostructure feature internal optical losses amounting to 0.6 cm−1; the divergence in the plane perpendicular to the p-n junction is 23°. In the continuous lasing mode at room temperature, a linear power-current characteristic is obtained at an output optical power as high as 7 W.

Low-temperature (

AlInSb layers are grown on highly lattice-mismatched GaAs (100) substrates by molecular-beam epitaxy (MBE) and studied in situ by reflection high-energy electron diffraction and ex situ by scanning and transmission electron microscopy (SEM and TEM). It is shown that one feature of AlInSb/GaAs heterostructure features is a high probability of forming microtwins; methods for decreasing their concentration are proposed. To initiate AlInSb growth on GaAs substrates under high lattice-mismatch (∼14.5%) conditions and to stimulate the transition to 2D growth, the GaAs layer surface was preliminarily exposed to an antimony flux followed by deposition of an intermediate AlSb buffer layer. The optimization of initial MBE growth stages of Sb-containing layers on the GaAs surface allows a decrease in the defect density in the GaAs/AlInSb heterostructures more than by two orders of magnitude, including a drastic decrease in the microtwin density. Optimal MBE growth conditions for Al x Al1 − x Sb are determined in a wide composition range (0 < x < 0.3). The TEM and SEM studies confirm the high structural quality of grown GaAs/AlInSb heterostructures. Hall-effect measurements showed the dependence of the carrier mobility and concentration on the aluminum content in AlInSb layers and allowed preliminary conclusions on scattering mechanisms.

The fracture patterns of active elements of pulsed green lasers with transverse electron-beam pumping, based on ZnSe-containing quantum-size structures, have been investigated. The fracture in the form of thin (∼1 μm) and long (to 100–150 μm) filaments can be explained by the self-focusing of the intrinsic laser radiation in the semiconductor structure.

Comparative study of growth kinetics of the Al x Ga 1-x N (x=0-1) layers grown by plasma-assisted molecular beam epitaxy (PA MBE) under different growth conditions (group III to activated nitrogen and Al to Ga flux ratios) is presented. The strong influence of elastic stress on the surface morphology, growth rate and Al content in Al x Ga 1 -x N (x= 0-1) layers is most pronounced for the Al x Ga 1- x N films with high Al-content grown atop of the 2D-AlN buffer layer at near the unity flux ratio F III /F N ~1. The use of strong Ga-rich growth conditions with F III /F N ~ 1.6-2 for the growth of Al x Ga 1- x N/2D-AlN with high Al-content (x > 0.25) allows one to reduce the strain effect as well as provide smooth surface morphology and precise control of Al content in the Al x Ga 1-x N (x=0-1) layers by employing a simple ratio x=F Al F N .

Exciton photoluminescence spectra, photoluminescence excitation spectra, and magnetophotoluminescence spectra of single (GaAs/AlGaAs/ZnMnSe) and double (GaAs/AlGaAs/ZnSe/ZnCdMnSe) heterovalent quantum wells formed by molecular beam epitaxy are studied. It is shown that the exciton absorption spectrum of such quantum wells mainly reproduces the resonant exciton spectrum expected for usual quantum wells with similar parameters, while the radiative exciton recombination have substantial distinctions, in particular the additional localization mechanism determined by defects generated by heterovalent interface exists. The nature of these localization centers is not currently clarified; their presence leads to broadening of photoluminescence lines and to an increase in the Stokes shift between the peaks of luminescence and absorption, as well as determining the variation in the magnetic g factor of bound exciton complexes.

We have demonstrated optically pumped room-temperature pulse lasing at 300.4 nm from an AlGaN-based multiple-quantum-well (MQW) structure grown by plasma-assisted molecular beam epitaxy on a c-sapphire substrate. The lasing was achieved at the threshold peak power of similar to 12 MW/cm(2). The MQW structure involved AlGaN/AlN short-period super-lattices to decrease the threading dislocation densities from 10(11) down to 10(9)-10(10) cm(-2). Studies of time-resolved photoluminescence (TRPL) spectra and cw PL temperature dependences (10-300K) of different MQW structures, as well as numerical calculations of the optical gain and confinement in the laser structure allowed us to conclude about the optimum design of AlGaN-based MQW structures for the lower threshold UV lasing.

The violet-green laser converter based on a molecular-beam-epitaxy (MBE) grown CdSe quantum dot (QD) laser heterostructure pumped by a commercial InGaN laser diode (LD) emission has been fabricated and studied in detail. The optimized II-VI laser heterostructure consists of asymmetrical ZnSe/ZnSSe superlattice (SL) waveguide and active region comprising five CdSe QD sheets (QDS) placed in the centre of 2-nm-thick ZnSe quantum wells. The new laser structure design provides both a high homogeneity of optical pumping of the CdSe QDS due to tunnelling of charge carriers between the QDS separated by 5-nm-thick ZnSe/ZnSSe/ZnSe barriers and high optical confinement factor. Optimization of both cavity length of the II-VI laser and parameters of optical focusing system to obtain a narrow stripe with the length slightly exceeding the cavity length has been performed. As a result, the maximum achieved quantum efficiency and pulse output power in green have been as high as 8% and 65 mW, respectively.

An increase in the rate of spontaneous recombination of excitons localized in films of InGaN solid solution due to interaction with a plasmon localized in a gold nanoparticle was experimentally observed. The particle is positioned near the surface with the help of a near -field scanning optical microscope or in the result of chemical precipitation from a colloidal solution. Precise positioning of a plasmonic particle allows single excitons with 1—2 meV-wide radiation lines to be revealed and amplified.

Pulsed heating of an active element of a low-threshold electron-beam-pumped laser based on nanostructures of II–VI compounds is measured and calculated. It is shown that the observed heating by ∼18°C agrees satisfactorily with the numerical calculation results and is explained by the heat removal during the pump pulse to a highly heat-conducting substrate.

We report on the spectroscopic magnetooptical studies of spin dynamics in diluted magnetic semiconductor (DMS) GaAs / AlGaAs / ZnSe / ZnCdMnSe heterovalent double quantum wells (QW). The transients of circularly polarized photoluminescence in an external magnetic field are detected in the structures with different widths of the GaAs QW. The analysis of the data, performed within the rate-equation model, has allowed separate estimations of the spin relaxation rate of localized electrons and holes. The spin flip of the electrons confined in the DMS ZnCdMnSe QW is faster than 20 ps, whereas the spin flip of the heavy hole localized in the GaAs QW is as long as ~9 ns. The long spin flip of the holes is presumably governed by their strong 3-dimensional localization.

Lasers that emit in the 1.3 μm wavelength range and include the active region based on InAs quantum dots were grown by the method of molecular-beam epitaxy and have been studied. The cavity includes a multilayer interference reflector, which brings about the fact that a large factor of optical confinement and low leakage losses are obtained only for the light propagating at some angle and, consequently, having a strictly definite wavelength. It is shown that, due to the use of such a waveguide structure, the temperature shift of the lasing wavelength is 0.2 nm/K, which is 2.5 times smaller than this shift in the lasers with quantum dots and with a conventional structure of the waveguide. The lasers with the stripe-contact width W = 10 μm exhibited the spatially single-mode emission, which verifies the advantages of the suggested nonconventional structure of the optical waveguide.

Al-rich AlGaN layers and quantum well (QW) structures with a reasonable structural quality have been grown by plasma-assisted molecular beam epitaxy (PA-MBE) under metal-rich stoichiometric conditions directly on c-sapphire. The bowing parameter of 1.1 eV for the compositional dependence of AlGaN band gap energy has been determined using an electron-probe microanalysis, Raman spectroscopy and optical transmission spectroscopy. A successful application of a sub-monolayer digital-alloying (SMDA) technique in PA-MBE for fabrication of AlGaN-based multiple QW structures, including deep-UV MQW light-emitting diodes, has been demonstrated for the first time. These structures exhibit both photo- and electroluminescence in the spectral range of 300–320 nm at room temperature.

Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al x Ga1 − x N/Al y Ga1 − y N quantum wells. Structural and optical properties of the Al x Ga1 − x N layers in the entire range of compositions (x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al2O3 substrates, heterostructures for light-emitting diodes with Al x Ga1 − x N/Al y Ga1 − y N quantum wells (x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm.

Emission characteristics of an electron-beam-pumped Cd(Zn)Se/ZnMgSSe semiconductor laser are studied. The laser’s active region consists of a set of ten equidistant ZnSe quantum wells containing fractional-monolayer CdSe quantum-dot inserts and a waveguide formed by a short-period superlattice with the net thickness of ∼0.65 μm. Lasing occurs at room temperature at a wavelength of 542 nm. Pulsed power as high as 12 W per cavity face and an unprecedentedly high efficiency of ∼8.5% are attained for the electron-beam energy of 23 keV.

Electron beam pumped (EBP) semiconductor lasers using ZnSe-based structures as active elements look very promising for the development green lasers because of no requirements of both p-n junction and low-resistivity contacts. Another advantage of EBP lasers is that the maximum conversion efficiency of electron beam energy to light is of ~30%. The possibility of using ZnSe-based quantum-size heterostructures for EBP green lasers demonstrated during last decade. Thus, room-temperature lasing at Ee

Experimental and theoretical studies of triple-quantum-well structures implementing a prototype active element for a novel type of unipolar laser were carried out. Such a laser, whose design was suggested by us previously, is based on highly asymmetric quantum wells (with barriers of noticeably different heights). It is shown that application of an external electric field to the structures under study leads to an effect similar to the dimensionality-switching effect in a structure with optimum parameters. Despite the fact that barrier thicknesses in the structures under study exceed considerably the values corresponding to the optimum structure, the matrix-element product that determines the gain remains sufficiently large (175–200 A2 as compared to 250 A2 in the optimum structure) in a wide range of electric fields.

High concentration of two types of P donors up to 1017 cm-3 in SiC enriched with 30Si after neutron transmutation doping (NTD) has been achieved. It was established that annealing at sufficiently low temperature of 1300oC, that is 500-600°C lower compared with annealing of NTD SiC with natural isotope composition, gives rise to the EPR signal of shallow P donors, labeled sPc1, sPc2 and sPh. The correlated changes of the EPR spectra of the three sP centres in all the experiments and the qualitative similarities with spectra of shallow N donors prove that these centres have shallow donor levels and a similar electronic structure and belong to different lattice sites. The annealing at 1700°C results in a transformation of one type of P donors (sPc1, sPc2 and sPh) into another type having low temperature EPR spectra labeled dP.

In x Ga 1-x N epilayers (0

We report on the molecular beam epitaxy growth of optically pumped Cd(Zn)Se/ZnMgSSe laser heterostructures with CdSe/ZnSe quantum dots in the active region, emitting in the green spectral range. The lasing threshold as low as 2.5 kW/cm 2 and the external quantum efficiency of 43%, maximum pulse power of 22.35 W is demonstrated.

The technique of preparation of nanostructures with InSb quantum dots in an InAs(Sb) matrix, emitting in the mid-IR range upon optical and injection pumping, by molecular beam epitaxy is considered and the structural and optical properties of these nanostructures are investigated. The characteristics of the first injection lasers based on III–V/II–VI hybrid heterostructures with InSb/InAs(Sb) quantum dots in the active region are reported.

Electron spin resonance (ESR) is used to study the neutron transmutation doping of silicon crystals enriched with 30Si isotope: phosphorus donors and radiation defects produced in the course of transmutational doping are observed. The ESR signals related to the phosphorus uncontrolled impurity in 30Si before transmutational doping (the P concentration is ∼1015 cm−3) and phosphorus introduced by neutron irradiation with doses ∼1 × 1019 cm−2 and ∼1 × 1020 cm−2 (the P concentrations are ∼5 × 1016 and ∼7 × 1017 cm−3, respectively) are studied. As a result of drastic narrowing of the phosphorus ESR lines in 30Si, the intensity of lines increased appreciably, which made it possible to measure the phosphorus concentration in the samples with a small volume (down to 10−6 mm−3). The methods for determining the concentration of P donors from hyperfine structure in the ESR spectra of isolated P atoms, exchange-related pairs, and clusters that consist of three, four, and more P donors are developed. In the region of high concentrations of P donors, in which case the hyperfine structure disappears, the concentration of P donors was estimated from the exchange-narrowed ESR line.

Phosphorus-doped silicon 30Si monoisotope samples with a highly homogeneous impurity distribution at a concentration of 5 × 1016 cm−3 were obtained for the first time by means of neutron transmutation doping.

The degradation of blue light emitting diodes (LEDs) with different structural disorder based on MQW InGaN/GaN grown by MOCVD on sapphire has been investigated. New approach to analyze the degradation has been used. It takes into account the structural disorder determined by the extended defect system relaxation and related with poor coalescence of the mosaic structure domains. The results obtained leads to assumption that the migration and segregations of Ga on domain dislocation boundaries of the mosaic structure and the change of energy activation of Mg related centers are important reasons of degradation for all types of LEDs The fastest degradation for poor ordered LEDs was observed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

MBE growth and study of optical and structural properties of (ZnSe/MgS)/ZnCdSe distributed Bragg reflectors with λ = 520 nm and Rmax = 97% are presented. The samples were grown pseudomorphically on GaAs (001) substrate using ZnS as a sulphur source. The details of MBE growth of such structures are discussed. Scanning electron microscopy, X-ray diffraction and optical measurements demonstrate good optical and structural characteristics of the Bragg reflectors. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence (PL), PL excitation (PLE) spectra as well as internal laser characteristics of CdSe quantum dots (QDs) in ZnSe matrix grown by molecular beam epitaxy (MBE) and multi-cycle migration enhanced epitaxy (MEE) were investigated. The peak PL intensity of the CdSe QDs grown by MEE in an asymmetric waveguide is by one order of magnitude more than that of the CdSe QDs grown by MBE in a symmetric waveguide. As a result, the laser characteristics have been significantly improved. The internal laser parameters were estimated to be: ΓG0 ∼ 66 cm–1, ηi ∼ 13–17%, αi ∼ 5–15 cm–1 for MBE CdSe QDs and ΓG0 ∼ 69 cm–1, ηi ∼ 42%, αi ∼ 2–10 cm–1 for MEE CdSe QDs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

It was found that in the Cd(Zn)Se/ZnMgSSe heterostructures with QD-like CdSe insertions in the lasing regime the structure changes take place manifesting itself, first, in the irreversible blue shift of the laser radiation spectra. This process depends on excitation intensity and on the cavity length, correlating with the inherent radiation density in the cavity. At excitation densities above 250 kW/cm2, the reduction of the radiative efficiency was observed. The second process is the increase of radiation intensity during laser operation under certain excitation conditions caused by the self-annealing of the laser structure induced by the inherent laser light and resulting in a decrease of the laser threshold by about 15–20%. Choosing the appropriate excitation regime, one may prolong the lifetime of this type of lasers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Plasmonic resonances in In-enriched nano-particles, spontaneously formed during growth, can dramatically modify optical properties of InN. Experimental support for this is provided from detailed studies of absorption and infrared emission in InN. In particular, thermally detected optical absorption and photoluminescence excitation spectroscopy reveal a peak below the region of strong absorption in InN. A higher-energy part of the infrared emission having a noticeable p-polarization is markedly enhanced with excitation along the surface. These peculiarities are discussed in terms of the Mie resonances, arising in metallic spheroids with different aspect ratio, and their coupling with recombining states, whose strength depends on energy separation between the states and the resonances.

MBE growth and studies of structural, photoluminescence and laser characteristic of Cd(Zn)Se/ZnMgSSe quantum disk optically-pumped laser heterostructures of a modified design are presented. The design changes include more homogeneous CdSe quantum-disk-sheet active region grown by modified migration enhanced epitaxy, rising the thickness and band gap of ZnMgSSe cladding layers, and a choice of proper place for the active region in the superlattice waveguide. Minimum laser threshold, maximum external quantum efficiency and maximum output power of 4.8 kW/cm2, 32%, and 21 W from both facets, respectively, have been achieved at 300 K. The laser internal loss has been estimated as small as 1–2 cm–1. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

InN is a unique material with a tendency for spontaneous formation of metallic indium particles during growth. To elucidate peculiarities related to plasmonic effects, the InN films have been grown either with or without such particles by molecular beam epitaxy using different growth regimes. Studies of the films have demonstrated that their optical properties are influenced by both absorption and electromagnetic enhancement related to the metallic clusters. Basic optical parameters of InN with the metallic inclusions are considered in relation to a cluster shape and orientation with respect to the electric field vector. The origin of infrared emission is discussed.

Molecular beam epitaxial growth of InSb sub-monolayer insertions in an InAs matrix, exhibiting intense mid-IR photoluminescence (PL) up to room temperature, is reported. The InSb insertions are fabricated by an exposure of the InAs surface to an antimony Sb 4 flux. The nominal thickness of the insertions grown at different temperatures (400-485 °C) changes in the 0.6-1 monolayer range, resulting in the emission wavelength variation from 3.9 to 4.3 μm at 300 K. An integral PL intensity drop from 80 to 300 K does not exceed 20 times. The laser emission at a wavelength of 3.08 μm (T=60K) with the threshold current density of 3-4kA/cm 2 under pulse injection pumping has been demonstrated in a hybrid p-AlGaAsSb/InAs/n-CdMgSe double heterostructure with the multiple type II InSb/InAs nanostructures in the active region.

The conclusion which is drawn from the EPR line broadening and narrowing of the N shallow donor in an isotope enriched and non-enriched 4H-SiC and 6H-SiC crystals along with previous ENDOR results shows that the spin-density distribution over the C and Si nuclei differs between the 4H-SiC and 6H-SiC polytypes. The main part of the spin density in 4H-SiC is located on the Si sublattice. In contrast, in 6H-SiC the main part of the spin density is located on the C sublattice. An explanation for the difference in the electronic wave function of the N donor in 4HSiC and 6H-SiC can be found in the large difference in the band structure of two polytypes and in the position of the minima in the Brillouin zone.

We demonstrate that nonstoichiometry is one of the main reason of strong deviation of the InN optical gap in the 0.7 – 2 eV range, with N/In 1 corresponding to the lower and higher energies, respectively. The phenomenon is discussed in terms of atomic orbital energies, which are strongly different for indium and nitrogen, therefore both excess atom incorporation and elimination could change the optical gap. We estimate such trends using the approximation of the empirical nearest-neighbor tight binding theory. It is also demonstrated that resonant absorption in In-enriched regions is an additional factor lowering an effective absorption edge. InN is an artificial material, whose thin films are formed by modern high-purity technologies. No bulk crystals of reasonable optical quality exist so far. In spite of recent breakthroughs in its study, debates on the basic properties of InN continue. Among these, is the exceptional variation of its experimental gap energy over a huge spectral range from ~0.7 up to 2 eV. The theoretical band-gap values, being strongly dependent on the model used, are also varied in the wide range. In particular, 2 eV [1], 1.55 eV [2] and ~0.7 eV [3] had been reported. At present the 0.7 eV value is commonly accepted, although the narrowgap InN possesses some unusual properties, such as disagreement with the common cation/anion rule [4], extraordinary position of the universal hydrogen acceptor/donor crossover level [5], superconductivity [6], high carrier mobility in layers with a huge defect density >10

We report on room temperature operation of green electron beam pumped semiconductor lasers based on multiple ZnSe quantum wells with CdSe quantum disk sheets, embedded in the ZnSSe/ZnSe alternately-strained superlattice waveguide. An efficiency of 4% per facet at electron beam energies of 18–21 keV was achieved. The output pulse power up to 12 W was detected. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the molecular beam epitaxy (MBE) growth and luminescence properties of tensile-strained type II GaAs/GaSb 1− x As x (0 x 1− y Sb y alloyed quantum wells (QWs) or self-organized formation of quantum dots (QDs). Both QW and QD nanostructures exhibit bright photoluminescence in the 1.5–2.2 μm range. AlGaSbAs laser diodes with GaAs/GaSb nanostructures in the active region have also been fabricated. The laser diode incorporating a 1.1 ML-GaAs/13 ML-GaSb superlattice in the active region shows room-temperature lasing at a wavelength of 1.85 μm under pulsed mode operation.

Characteristics of a scanning pulsed green laser based on heterostructures containing ZnSe pumped by an electron beam with 200-ns duration and 8-keV energy are studied. If the active element is at room temperature, the scanning frequency is 20 Hz, and the repetition rate is 3 kHz, the average power of laser radiation is 1.6 mW, provided that the pulsed power is 2.7 W.

Photoluminescence and lasing at a wavelength of λ=510–530 nm (green spectral region) in Cd(Zn)Se/ZnMgSSe structures with a different design of the active region are studied in a wide range of temperatures and nitrogen laser pump intensities. A minimal lasing threshold of 10 kW/cm2, a maximal external quantum efficiency of 12%, and a maximal output power of 20 W were obtained for the structure with the active region composed of three ZnSe quantum wells with fractional-monolayer CdSe inserts. The lasers exhibited a high temperature stability of the lasing threshold (characteristic temperature T0=330 K up to 100°C). For the first time, an integrated converter composed of a green Cd(Zn)Se/ZnMgSSe laser optically pumped by a blue InGaN/GaN laser that is grown on a Si (111) substrate and incorporates multiple quantum wells is suggested and studied.

We report on a close correlation between the growth conditions of InN/Al2O3 (0 0 0 1) epilayers grown by plasma-assisted molecular beam epitaxy (MBE), their optical properties in the IR range, and the In clustering in the layers. High-spatial resolution techniques, namely micro-cathodoluminesesence, back-scattered electron imaging and energy dispersive X-ray analysis, were used to establish this correlation. The In-rich growth conditions, achieved by increasing either the growth temperature or the effective In/N flux ratio, causes the In clustering in InN, responsible in our samples for the 0.7-0.8 eV luminescence and IR optical absorption. Growth under In/N = 1: 1 conditions slightly shifted to the N-rich side generally produces InN layers without visible In clusters, having an optical absorption edge around 1.4 eV. A possible mechanism of In cluster formation is suggested on the basis of thermodynamic considerations for InN MBE growth. (C) 2004 Elsevier B.V. All rights reserved.

In the cyclotron resonance (CR) spectra of two-dimensional (2D) electrons in InAs quantum wells, the CR line splitting is observed. The splitting is found to be an oscillating function of magnetic field. The oscillations do not correlate with the filling factor. The experimental results are interpreted in terms of the spin-orbit splitting in the presence of a built-in electric field appearing due to the asymmetry of the quantum-well potential. From the splitting of the CR line, the spin-orbit coupling constant αso is determined. The resulting value agrees well with the value obtained for the same sample from the Shubnikov-de Haas oscillations. The role of the resonance interaction of charge carriers in the well with the interface donor states is discussed.