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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. [ABSTRACT FROM AUTHOR]

Provides information on a study that examined resonant luminescence in ultrathin InAs quantum-well structures. Sample growth and characterization; Results and discussion on the study.

We report on the unusually large blue shift of electroluminescence spectrum with 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 MOVPE on n-GaSb:Te substrate. The rise of drive current from 20 to 220 mA led to shift of the electroluminescence spectrum maximum towards 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 AlSb/p-GaSb heterointerface. Energy of radiative transition was linearly dependent on applied voltage. In the drive current range of 50–220 mA electroluminescence blue shift was accompanied by the spectrum narrowing by 40 meV and noticeable change of the spectrum shape. With rise in drive current superlinear increase of electroluminescence intensity caused by the nonlinear dependence of tunneling radiative recombination rate on transition energy was observed at 300 and 77 K. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Å2 as compared to 250 Å2 in the optimum structure) in a wide range of electric fields. [ABSTRACT FROM AUTHOR]

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 10kW/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. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

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. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Heterostructures with a single InAs[sub 1-x]Sb[sub x]/AlSb[sub 1-y]As[sub y] quantum well (QW) on (001) GaSb substrates have been grown by MBE and studied using X-ray diffraction, transmission electron microscopy, and photoluminescence (PL) spectroscopy. High-intensity PL was observed at a temperature of 80 K, with a peak half-width of 30-50 meV and a peak wavelength in the range from 2 to 4.5 µm, depending on the QW width, which varied between 4 and 20 nm, respectively. The fundamental absorption edge of such QWs was calculated for a wide range of alloy compositions, x and y. Good correlation between the experimental and calculated dependences of the band gap on the InAsSb/AlSbAs QW thickness was obtained. [ABSTRACT FROM AUTHOR]

Splitting of the cyclotron resonance (CR) line is observed in the electron CR spectra of InAs/GaSb heterostructures containing tunneling-coupled electron and hole layers. This splitting is interpreted to be a manifestation of a hybridization gap arising as a result of anticrossing of the Landau levels of electrons and holes when their wave functions overlap. The energy splitting of the CR lines is correlated with the magnitude of the overlap and agrees with theoretical estimates of the hybridization gap width. © 1999 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the results of an experimental study of molecular-beam epitaxy of ZnSe-based laser heterostructures with a new structure of the active region, which contains a fractionalmonolayer CdSe recombination region in an expanded ZnSe quantum well and a waveguide based on a variably-strained, short-period superlattice are reported. Growth of a fractionalmonolayer CdSe region with a nominal thickness of 2-3 ML, i.e., less than the critical thickness, on a ZnSe surface (Δa/a ∼7%) leads to the formation of self-organized, pseudomorphic, CdSe-enriched islands with lateral dimensions ∼10-30 nm and density ∼2 × 10[sup 10] cm[sup -2], which serve as efficient centers of carrier localization, giving rise to effective spatial separation of defective regions and regions of radiative recombination and, as a result, a higher quantum efficiency. Laser structures for optical pumping in the (Zn, Mg) (S, Se) system with a record-low threshold power density (less than 4 kW/cm² at 300 K) and continuous-wave laser diodes in the system (Be, Mg, Zn) Se with a 2.5 to 2.8-ML-thick, fractionalmonolayer CdSe active region have been obtained. The laser structures and diodes have an improved degradation resistance. [ABSTRACT FROM AUTHOR]

The optical properties of structures with InAs islands and narrow GaAs quantum wells in an AlGaAs host have been investigated. The InAs islands were formed by depositing a layer of InAs with an effective thickness less than one monolayer. The effect of an exciton waveguide and the onset of lasing due to optical pumping in the red spectral range are demonstrated in structures without external optical confinement by layers with a lower refractive index. [ABSTRACT FROM AUTHOR]

A method is proposed to increase the emission wavelength from structures grown on GaAs substrates by inserting a strained InAs quantum dot array into an external InGaAs quantum well. The dependence of the luminescence peak position on the active region design was investigated for structures grown by this method. Room-temperature photo- and electroluminescence spectra in the 1.3-µm wavelength range are compared. [ABSTRACT FROM AUTHOR]

The optical properties of structures with submonolayer inclusions of CdSe in a Zn(S,Se) matrix are studied. The submonolayer coating consists of a group of nanosized (40 Å) islands with a height of one monolayer. The exciton oscillator strength of multiple submonolayer CdSe-ZnSSe structures is substantially increased compared to the case of a uniform quantum well of comparable thickness and composition. In submonolayer structures lasing takes place immediately next to the energy of the ground state of the heavy exciton, in contrast with ordinary quantum wells of ZnCdSe, where it is strongly shifted to longer wavelengths by the energy of a single optical phonon. This effect results from the removal of the momentum selection rules during radiative recombination of excitons in submonolayer structures. [ABSTRACT FROM AUTHOR]

The possibility of locally varying the potential energy of the electrons and holes localized in a quantum well by a quantum-dot array deposited in the immediate vicinity of the quantum well is demonstrated. These changes in the potential energy are induced when a strain arises in the quantum-dot region. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The mechanism of oscillations of the half-width and intensity of the cyclotron resonance (CR) line of electrons in a semimetal quantum well based on an InAs/AlSb/GaSb heterostructure is investigated experimentally and theoretically. It is shown that the oscillations of the CR spectrum are due to mixing of states of the spatially separated two-dimensional electrons and holes. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on AlGaN multiple-quantum-well separate confinement laser heterostructures grown by plasma-assisted molecular-beam epitaxy directly on c-sapphire at low temperatures (<800 °C). Threading dislocation density was reduced down to 109–1010 cm-2 owing to both intentionally introduced strained AlGaN/AlN superlattices and self-organized blocking structures in the AlGaN step-graded buffer layers. The quantum wells were fabricated by a submonolayer digital alloying technique. Calculations of the optical gain and confinement in the optically pumped laser structures yielded its optimum design comprising an asymmetric waveguide. Lasing at 303 nm with the relatively low threshold excitation density of 0.8 MW/cm2 at 295K has been achieved. [ABSTRACT FROM AUTHOR]

We report a time-resolved study of the recombination dynamics in molecular beam epitaxy grown ZnO/ZnMgO single quantum wells (SQWs) of 1.0–4.5 nm width. The SQWs exhibit different emission properties, depending on both the well width and defect density. Stimulated emission has been achieved at room temperature in a separate confinement double heterostructure having a 3 nm wide SQW as an active region. It has been found that a critical parameter for the lasing is the inhomogeneous broadening of both QW and barrier emission bands. [ABSTRACT FROM AUTHOR]

Spin depolarization of a ZnCdSe quantum-well spin detector (SD) in ZnMnSe/ZnCdSe light-emitting quantum structures is investigated by cw and time-resolved optical orientation spectroscopy. It is shown that spin depolarization is governed by three distinct spin relaxation processes with the corresponding polarization decay times of 850, 30, and <10 ps. The dominant and the fastest process is attributed to spin relaxation accompanying energy relaxation of hot excitons (and hot carriers) within the SD, providing evidence that it can be an important source of spin loss, leading to the observed limited efficiency of optical spin injection in the structures. [ABSTRACT FROM AUTHOR]

Asymmetric (6.7–300)-nm-thick InAs quantum wells (QWs) confined between AlAsSb and CdMgSe barriers have been fabricated by molecular-beam epitaxy. A special procedure of the CdMgSe-on-InAs growth initiation, exploiting an ex situ S passivation of InAs and in situ deposition of an ultrathin ZnTe buffer layer, results in the fabrication of high quality structures with a density of extended defects below 106 cm2. QW photoluminescence studies demonstrate a confinement effect and confirm the type I band alignment at the heterovalent InAs/CdMgSe interface mediated by the ZnTe interlayer. Observation of Shubnikov de Haas oscillations of magnetoresistance for an asymmetric 19-nm-thick InAs QW indicates an existence of the two-dimensional electron gas with the low-temperature sheet electron density of 1.3×1012 cm-2 and the mobility as high as ∼10 000 cm2/V s. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Mid-infrared electroluminescence (EL) is observed from multiperiod bilayer type-II InAs/AlGaSb structures with the effective interlayer separation controlled by bias. The emission with powers in the microwatt range is characterized by a linear dependence of the photon energy on the bias. By measuring the temperature and current dependence of EL, we find evidence that the EL emission results from recombination of holes in AlGaSb quantum wells (QWs) with electrons occupying two different quantum states in InAs QWs. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Two-photon absorption of 1.55 gm light in quantum-well InGaAs/InP laser heterostructures has been studied. The highest achieved nonlinear response was 0.78 nA/mW². The minimum detectable peak power of 60 µW allows for the effective use of waveguides of this type as detectors in optical autocorrelators for studying temporal characteristics of low-power signals. [ABSTRACT FROM AUTHOR]

Bulk BeCdSe layer lattice-matched to a GaAs substrate, as well as a BeCdSe/ZnSe quantum well (QW) structure have been grown using the submonolayer digital alloying mode of molecular beam epitaxy. The structures have demonstrated bright photoluminescence up to room temperature and good structural quality. Stimulated emission under optical pumping has been obtained for a 2 nm BeCdSe/ZnSe multiple QW structure at 80 K. The bowing parameter of the energy gap of this ternary alloy has been estimated as about 4.5 eV. [ABSTRACT FROM AUTHOR]

Cyclotron resonance is measured in solitary type-II InAs-AlGaSb quantum wells grown by molecular-beam epitaxy under various growth conditions. Quantum oscillations observed in the cyclotron resonance spectra in InAs-GaSb samples are attributed to scattering by a shortrange potential due to roughness of the heterointerface. A new method based on measurement of the cyclotron resonance spectra is proposed for assessing the quality of the heterointerface. [ABSTRACT FROM AUTHOR]

Spontaneous emission has been observed for the first time as a result of interband transitions of holes and electrons between size-quantization levels in vertically coupled quantum dots and also as a result of transitions from quantum-well states to a quantum-dot level. The spectral range of the emission was in the far-infrared (λ ... 10-20 µm). The long-wavelength emission was only recorded simultaneously with short-wavelength interband emission (λ ... 0.94 µm) in InGaAs/AlGaAs quantum-dot laser structures at above-threshold currents. [ABSTRACT FROM AUTHOR]

The electroluminescent properties of quantum-well diode structures on staggered type-II heterojunctions in the InAs/GaSb system, obtained by molecular-beam epitaxy on InAs substrates, are investigated. Electroluminescence is observed in the spectral range 3-4 µm at T = 77 K. It is found that emission bands due to recombination transitions involving electrons from the size-quantization levels of both the self-matched quantum wells at the InAs/GaSb type-II heterojunction and of the square quantum wells in short-period superlattices. [ABSTRACT FROM AUTHOR]