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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]

The lasing of an injection-pumped p-AlGaAsSb/n[SUP0]-InAs/n-CdMgSe double hybrid heterostructure in the mid-IR range is demonstrated for the first time. The lasing wavelength λ is 2.775 μm, and the threshold current density J[SUBth] = 3-4 kA/cm[SUP2] at T = 77 K. The structure grown by two-stage molecular-beam epitaxy is characterized by extremely high (∼1.5 eV) asymmetric potential barriers for electrons and holes in the InAs active region. The output power of spontaneous emission for round-mesa diodes atT = 300 K was no less than 0.3 mW. [ABSTRACT FROM AUTHOR]

Optical properties of GaN layers grown by the molecular-beam epitaxy (MBE) and chloride-hydride vapor-phase epitaxy (CHVPE) have been studied, and the quality of two types of samples has been compared. The photoluminescence spectra have an excitonic nature for both types of layers. To determine precisely the nature of exciton transitions, the reflectance spectra were studied. A key point was the investigation of phonon-assisted exciton luminescence, which provides information on the density distribution of the exciton states. Temperature dependences of the exciton transition energy and the ratio of intensities of one- and two-phonon replicas were studied. The high quality of both types of layers has been confirmed, though the concentration of acceptors in MBE-grown samples is higher than in CHVPE samples. [ABSTRACT FROM AUTHOR]

A ZnSSe/ZnMnSe type-II semimagnetic superlattice was pseudomorphically grown via molecular beam epitaxy on a GaAs substrate. The superlattice-layer thicknesses and compositions were chosen so that compressive strains in the ZnMnSe layer compensated tensile strains in the ZnSSe layer. The photoluminescence spectra in an external magnetic field demonstrate the effect of "giant Zeeman splitting of an exciton". Simulation of the luminescence-line shift in a magnetic field allowed us to determine more accurately the band offsets at the ZnSSe/ZnMnSe interface. [ABSTRACT FROM AUTHOR]

Atomic-force microscopy was applied to compare the topographies of naturally oxidized surfaces of GaAs(100) substrates and those substrates treated with aqueous solutions of sodium sulfide in various stages of their preparation for growth of ZnSe-based heterostructures by molecular beam epitaxy (MBE). It was found that annealing of oxidized substrates strongly disrupts the surface planarity and leads to the appearance of pits with density of 10[sup 10] cm[sup -2]. The pit density can be reduced by two orders of magnitude by treating the substrate surface with an aqueous solution of Na[sub 2]S. Transmission electron microscopy demonstrated that sulfidation of GaAs substrates makes it possible to reduce the number of stacking faults at the ZnSe/GaAs interface to ∼3 × 10[sup 5] cm[sup -2] and, correspondingly, to improve the structural perfection of MBE-grown II-VI layers and heterostructures. [ABSTRACT FROM AUTHOR]

The fabrication of new hybrid AlAsSb/InAs/Cd(Mg)Se heterostructures by molecular beam epitaxy and investigation of their structural, luminescent, and transport properties are reported for the first time. These structures show intense luminescence both in the infrared and in the visible regions of the spectrum. This factor, taken together with structural data, indicates a heterointerface of high quality between the III-V and II-VI layers. A theoretical estimate is made of the relative positions of energy bands in the proposed hybrid structures, indicating that the InAs/CdSe interface is a type-II heterojunction, whereas the InAs/Cd[sub 0.85]Mg[sub 0.15]Se interface is a type-I heterojunction with a large valence band offset ΔE[sub v] ≈ 1.6 eV. The data obtained on the longitudinal electron transport at the InAs/Cd(Mg)Se heterointerface are in good agreement with the theoretical estimate. [ABSTRACT FROM AUTHOR]

The optical properties of structures containing InGaAs quantum dots in GaAs and AlGaAs matrices grown by molecular-beam epitaxy are investigated. It is shown that increasing the In content in the quantum dots has the effect of raising the energy of carrier localization and increasing the energy distance between the ground state and the excited states of carriers in the quantum dots. An investigation of the influence of postgrowth annealing on the optical properties of the structures shows that the formation of vertically coupled quantum dots and the use of a wide-gap AlGaAs matrix enhances the thermal stability of the structures. Moreover, high-temperature (830°C) thermal annealing can improve the quality of the AlGaAs layers in structures with vertically coupled InGaAs quantum dots in an AlGaAs matrix. The results demonstrate the feasibility of using postgrowth annealing to improve the characteristics of quantum dot lasers. [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 influence of the growth conditions during molecular-beam epitaxy and of the degree of lattice mismatch between the epilayer and the substrate on the formation of InGaAs islands on a Si(100) surface is studied. An increase in lattice mismatch (the InAs mole fraction) leads to an increase in the critical thickness corresponding to the onset of island growth, in contrast to the formation of InGaAs islands on GaAs(100). An increase in the deposition temperature also increases the critical thickness, whereas an increase in the arsenic pressure has the opposite effect. Structures containing an array of InGaAs islands in a Si matrix display a luminescence line in the range 1.2-1.3 µm, depending on the mole fraction of InAs. [ABSTRACT FROM AUTHOR]

The effect of partial ordering of impurities (correlated along one direction and uncorrelated along the other) on the kinetic coefficients is considered. It is shown that the geometry of the spatial impurity distribution by itself has no effect on the diffusion coefficient or conductivity for scattering by a spherically symmetric potential, and these coefficients remain the same as for an uncorrelated system of impurities. [ABSTRACT FROM AUTHOR]

A thermodynamic model is given for the molecular-beam epitaxy formation of InSb, GaAs, and AlAs heterointerfaces in (Al, Ga)Sb/InAs heterostructures. The maximum critical temperature of formation of a planar InSb-type heterointerface on an (Al, Ga)Sb layer, T ≈ 390 °C, is determined from a comparison of the pressure of Sb[sub 4] molecules in the external flux with their equilibrium value above a stressed monolayer on a heterointerface and is found to be in good agreement with existing experimental data. In contrast, the critical temperature of formation of a heterointerface of the AlAs (GaAs) type, corresponding to the onset of rapid reevaporation of As, is much higher than the growth temperatures normally used in molecular-beam epitaxy (350-550 °C). [ABSTRACT FROM AUTHOR]

Arrays of strained InAs islands in an (In, Ga)As matrix on an InP(100) substrate are synthesized by molecular-beam epitaxy, and their structural and optical properties are investigated. According to transmission electron microscope and high-energy electron diffraction data, the critical thickness corresponding to the onset of island growth is 3 monolayers. The resulting InAs islands are coherently strained, and their base diameter varies from 20 nm to 90 nm. The formation of islands produces in the photoluminescence spectra a dominant long-wavelength line, which shifts toward lower energies as the effective thickness of the InAs increases. The radiation emitted by the InAs islands spans a wavelength range of 1.65-2 µm. [ABSTRACT FROM AUTHOR]

A thermodynamic description of the molecular-beam epitaxial growth of quaternary III-V compounds with two group-V elements is proposed. A thermodynamic analysis of the growth of the compounds Ga[sub x]In[sub 1-x]P[sub y]As[sub 1-y] and GaP[sub y]As[sub 1-y] is carried out on the basis of the proposed method. [ABSTRACT FROM AUTHOR]

The influence of mismatch stress on the structural, optical, and transport properties of thick InGaAs layers grown on InP(100) substrates by molecular-beam epitaxy is investigated. It is found that layers having tensile stress can be grown with a greater mismatch than compressively stressed layers before plastic relaxation sets in. The critical mismatch for thick InGaAs layers is not described with sufficient accuracy by either the mechanical equilibrium model or the energy balance model. The range of mismatches required to obtain high carrier mobilities and high radiative recombination efficiencies in InGaAs layers grown on InP substrates is much narrower than the pseudomorphic growth range. The maximum mobilities and minimum widths of the photoluminescence peak are attained in layers matched with the substrate in terms of the lattice parameter and also in slightly gallium-enriched layers. The compositional dependence of the width of the band gap is investigated with allowance for the influence of stress. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on structural and optical properties of green (λ∼520 nm) ZnCdSe/ZnMgSSe optically pumped laser heterostructures with a Zn(Mg)SSe/ZnSe graded-index superlattice (SL) waveguide, grown by molecular beam epitaxy. The pseudomorphic 400 nm thick waveguide comprising a set of strained ZnMgSSe/ZnSe and ZnSSe/ZnSe SLs of different periods and barrier-to-well thickness ratios at each side of a ZnCdSe quantum well (QW) active region provides efficient transport of nonequilibrium carriers to the QW. This results in reduction in laser threshold down to the extremely low value of 1.5 kW/cm2 at 300 K and increasing the external quantum efficiency above 44%. [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]

We report on molecular beam epitaxial growth of InSb submonolayer insertions in an InAs matrix, exhibiting intense mid-IR photoluminescence (PL) up to room temperature (RT). The InSb insertions are fabricated by an exposure of InAs surface to an antimony Sb4 flux. The nominal thickness of insertions grown at different temperatures (TS=400–485 °C) ranges from 0.6 to 1.4 monolayer, as estimated from x-ray diffraction measurements of InSb/InAs multiple submonolayer structures. This gives rise to the variation of the emission wavelength within the 3.9–4.3 μm range at RT. An integral PL intensity drop from 77 K to RT does not exceed 20 times. [ABSTRACT FROM AUTHOR]

A mid-IR laser based on a hybrid pseudomorphic AlGaAsSb/InAs/CdMgSe heterostructure with a III-V/II-VI heterovalent interface at the 0.6-µm-InAs active region has been fabricated by molecular-beam epitaxy on p[sup +]-InAs substrate. It provides ∼1.5-eV asymmetric barriers for both electrons and holes in InAs, inhibiting carrier leakage from the active region. Despite a nonoptimal defect density at the CdMgSe/InAs interface (10[sup 6]-10[sup 7] cm[sup -2]), the structure demonstrates lasing at ∼2.78 µm (up to 100 K) under pulse injection pumping with the threshold current density of 3-4 kA/cm². The proposed design is promising for high-power mid-IR lasers operating at room temperature. [ABSTRACT FROM AUTHOR]

Molecular-beam epitaxy with a solid source was used to grow silicon layers enriched with [sup 28]Si and [sup 30]Si isotopes to 99.93 and 99.34%, respectively. Secondary-ion mass spectrometry and Raman scattering spectroscopy were applied to demonstrate the high isotopic purity and crystal perfection of the layers obtained. [ABSTRACT FROM AUTHOR]

A hybrid double heterostructure with large asymmetric band offsets, combining AlAsSb/InAs (as a III-V part) and CdMgSe/CdSe (as a II-VI part), has been proposed as a basic element of a midinfrared laser structure design. The p-i-n diode structure has been successfully grown by molecular beam epitaxy and has exhibited an intense long-wavelength electroluminescence at 3.12 μm (300 K). A less than 10 times reduction of electroluminescence intensity from 77 to 300 K indicates an efficient carrier confinement in the InAs active layer due to high potential barriers in conduction and valence bands, estimated as ΔE[sub C]=1.28 eV and ΔE[sub V]∼1.6 eV. The type of band lineups at a coherent InAs/Cd[sub 1-x]Mg[sub x]Se interface is discussed for 0≤x≤0.15. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It is shown that an array of two-dimensional islands is formed during the growth of ultrathin (∼1.5 monolayers) InSb layers on a GaSb (100) surface by molecular beam epitaxy. After the deposition of several InSb layers separated by narrow barriers, islands of subsequent rows are formed on top of islands of the first row (vertical correlation effect). The formation of islands is confirmed by analysis of the photoluminescence spectra. [ABSTRACT FROM AUTHOR]

Injection heterolasers based on quantum dots grown by molecular-beam epitaxy have been investigated. It is shown that the room-temperature threshold current density can be lowered to 15 A/cm² by decreasing the nonradiative recombination and increasing the degree of carrier localization. The density of states in structures with vertically coupled quantum dots was investigated by the electroabsorption method. [ABSTRACT FROM AUTHOR]

Molecular beam epitaxy was used to fabricate GaAsN/GaAs and InGaAsN/GaAs heterostructures, and the influence of the growth regimes on their characteristics was studied. It is shown that implantation of nitrogen causes a substantial long-wavelength shift of the radiation. The possibility of obtaining 1.4 µm radiation at room temperature was demonstrated using In[sub 0.28]Ga[sub 0.72]As[sub 0.97]N[sub 0.03]/GaAs quantum wells. [ABSTRACT FROM AUTHOR]

It is shown that GaN films can be grown by molecular-beam epitaxy with plasma activation of the nitrogen by a magnetron rf discharge in a specially constructed coaxial source with capacitive coupling. A growth rate of ∼0.1 µm/h is obtained on GaAs and sapphire substrates, and ways are found for optimizing the design of the plasma source in order to increase the growth rate. The electrophysical and luminescence properties of undoped epitaxial films are investigated at temperatures ranging all the way to room temperature. [ABSTRACT FROM AUTHOR]

We apply an exact electrodynamic theory to analyze experimental data on the emission enhancement in epitaxial semiconductor structures, induced by resonant interaction of emitting excitons with plasmons localized in a gold nanoparticle. Near-field scanning optical microscopy was employed to investigate the effect of the gold particle positioned near the surface of a rough InGaN film or a CdSe/ZnSe quantum dot heterostructure fabricated by molecular-beam epitaxy. It is shown that the frequently used quasistatic approximation is unable to explain the experimental data due to the inability to take into consideration the contribution of higher-order multipole plasmon resonances. In particular, it follows from the performed calculations that the observed effect of the emission enhancement owes mainly to the resonant interaction with the quadrupole and octupole plasmon modes in the spherical gold particle. The design of optimized metal-semiconductor structures is proposed. [ABSTRACT FROM AUTHOR]