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Quantum dots (QDs) formed on GaAs(100) substrates by InAs deposition followed by (Al,Ga)As or (In,Ga,Al)As overgrowth demonstrate a photoluminescence (PL) peak that is redshifted (up to 1.3 μm) compared to PL emission of GaAs-covered QDs. The result is attributed to redistribution of InAs molecules in the system in favor of the QDs, stimulated by Al atoms in the cap layer. The deposition of a 1 nm thick AlAs cover layer on top of the InAs-GaAs QDs results in replacement of InAs molecules of the wetting layer by AlAs molecules, leading to a significant increase in the heights of the InAs QDs, as follows from transmission electron microscopy. This effect is directly confirmed by transmission electron microscopy indicating a transition to a Volmer-Weber-like QD arrangement. We demonstrate an injection laser based on this kind of QDs. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Composite InGaN/GaN/InAlN quantum dots (QDs) have been formed and studied. The structural properties of thin InAlN layers overgrown with GaN have been analyzed, and it is shown that 3D islands with lateral sizes of ∼(20-30) nm are formed in structures of this kind. It is demonstrated that deposition of a thin InGaN layer onto the surface of InAlN islands overgrown with a thin GaN layer leads to transformation of the continuous InGaN layer to an array of isolated QDs with lateral sizes of 20-30 nm and heights of 2-3 nm. The position of these QDs in the growth direction correlates with that of InAlN islands. [ABSTRACT FROM AUTHOR]

GaN-based structures with InGaN quantum dots in the active region emitting in the near-ultraviolet region are studied. In this study, two types of structures, namely, with InGaN quantum dots in a GaN or AlGaN matrix, are compared. Photoluminescence spectra are obtained for both types of structures in a temperature range of 80–300 K and at various pumping densities, and electroluminescence spectra are obtained for light-emitting (LED) structures with various types of active region. It is shown that the structures with quantum dots in the AlGaN matrix are more stable thermally due to the larger localization energy compared with quantum dots in the GaN matrix. Due to this, the LED structures with quantum dots in an AlGaN matrix are more effective. [ABSTRACT FROM AUTHOR]

Mechanisms of InGaA1As solid solution decomposition stimulated by a purposely deposited layer of InAs quantum dots are studied. Decomposition of the solid solution results in an increase in the effective quantum dot size and the shift of the photoluminescence line to as far as 1.3 μm. When aluminum atoms are added to the solid solution, the effect of In atom "conservation" within the dots is observed, which also causes an increase in the effective dot size. [ABSTRACT FROM AUTHOR]

When an array of strained InAs nanoislands formed on a GaAs surface is overgrown by a thin (1-10 nm) layer of an indium-containing solid solution, stimulated decomposition of the solid solution is observed. This process causes the formation of zones of elevated indium concentration in the vicinity of the nanoislands. The volume of newly formed InAs quantum dots increases as a result of this phenomenon, producing a substantial long-wavelength shift of the photoluminescence line. This effect is enhanced by lowering the substrate temperature, and it depends weakly on the average width of the band gap of the solid solution. The indicated approach has been used successfully in achieving room-temperature emission at a wavelength of 1.3 µm. [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]

The modification produced in the structural and optical properties of vertically coupled In[sub 0.5]Ga[sub 0.5]As quantum dots in a GaAs matrix by increasing the number of deposited layers of quantum dots has been investigated. It was shown that the deposition of a sequence of In[sub 0.5]Ga[sub 0.5]As quantum-dot planes separated by narrow (of the order of the height of the quantum dots) GaAs layers gives rise to an interaction between neighboring vertically coupled quantum dots. This interaction shifts the photoluminescence line due to the recombination of nonequilibrium carriers via states of the quantum dots into the region of lower photon energies. [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]

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]

Conditions are investigated for the injection of arsenic into gallium nitride layers grown by metalorganic vapor-phase epitaxy. It is shown that the deposition of GaAs on a GaN surface relieves stresses in the GaN layer. The high-temperature overgrowth of a thin GaAs layer by a GaN layer causes As atoms to diffuse into the GaN, produces a thick, homogeneously doped GaN:As region, and creates a bright band in the photoluminescence spectrum with a maximum at ∼2.5 eV. [ABSTRACT FROM AUTHOR]

Structures having a set of planes with submonolayer InAs inclusions in an AlGaAs matrix were fabricated and studied. Lasing was observed as a result of optical excitation. It is shown that lasing takes place via the ground state of excitons localized at InAs islands and may be achieved without external optical confinement of the active region by wide-gap layers of lower refractive index. The low threshold excitation density shows that these structures may be used to develop low-threshold injection lasers in the visible range, exciton waveguides, and self-contained microcavities. [ABSTRACT FROM AUTHOR]

The photoluminescent properties of quantum dots formed in the deposition of an InSb thin film (1–3 monolayers) on GaAs(100) and GaSb(100) surface are investigated. The results indicate the importance of As–Sb substitution reactions in the formation of quantum dots on a GaAs surface. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

we present the results of fabrication of flip-chip LEDs with removed substrate from AlInGaN heterostructures grown on SiC/Si substrates synthesized by vacancy-matching atom substitution. It is shown that SiC/Si substrates are optimal from the viewpoint of matching lattice parameters, thermal conductivity, and optical characteristics of the material at a significantly lower cost. Therewith, the procedure of cutting wafers into individual chips and removal of the opaque silicon part of the substrate becomes easier, and the transparent SiC part of the substrate remaining on the chip surface creates a relief that facilitates light output. [ABSTRACT FROM AUTHOR]

Structural and optical properties of InAlN/GaN distributed Bragg reflectors grown by MOCVD on sapphire substrates are studied. The influence of growth conditions and thicknesses of the InAlN layers on structural properties of distributed Bragg reflectors is studied. It is shown that optimization of the conditions of epitaxial growth makes it possible to design InAlN/GaN distributed Bragg reflectors with a reflectance of more than 99% and a reflection maximum in the wavelength range of 460–610 nm. [ABSTRACT FROM AUTHOR]

The structural and optical properties of ultrathin Ge insertions in an Si matrix were studied. Transmission electron microscopy revealed the spontaneous formation of arrays of disk-shaped quantum dots (QDs) with a small lateral size (3-10 nm) at a nominal Ge insertion thicknesses, from submonolayer to nearly critical, for the transition to 3D growth by the Stranski-Krastanow mechanism. Optical study revealed type-I band alignment in these structures, which results from the strong contribution of the electron-hole Coulomb interaction overpowering the repulsion potential for an electron existing in the Ge conduction band. The small lateral size of QDs lifts the selection rule prohibiting indirect recombination in the inverse k space. At the same time, the high surface density of QDs (10[sup 12]-10[sup 13] cm[sup -2]) and the possibility of their stacking with the use of ultrathin Si spacers allows the obtainment of an ultrahigh volume density of QDs (up to 10[sup 19] cm[sup -3]), which is necessary to achieve stimulated emission in Si. A sample with stacked QDs formed by 0.7-nm-thick Ge insertions exhibited a superlinear increase of the photoluminescence (PL) intensity, accompanied by narrowing of the PL line. The doping of Ge-Si structures with donors allows for a drastic increase in the PL intensity at high temperatures, which prevents depletion of the active region in weakly localized electrons. [ABSTRACT FROM AUTHOR]

Structures with In(Ga)As quantum dots in the GaAs matrix obtained using molecular-beam epitaxy are investigated using photoluminescence (PL) measurements and transmission electron microscopy. The structures were subjected in situ to the procedure of the selective thermal elimination of defect regions. Based on the results of the analysis of luminescence properties, a method for evaluating the crystalline quality of structures using the measurements of PL intensity for the GaAs matrix at high temperatures (as high as 400 K) is suggested. Procedures for the elimination of defects are investigated, namely, the single-stage selective elimination of InAs defect islands at 600°C and a two-stage procedure. The latter procedure additionally includes selective overgrowth with a thin AlAs layer and high-temperature (650-700°C) heat treatment. The optimal conditions of the process, which permit the obtaining of structures with a relatively low defect density without a considerable decrease in the density of coherent quantum dots, are found. [ABSTRACT FROM AUTHOR]

Optical properties of structures with vertically coupled quantum dots grown by the combined submonolayer molecular-beam epitaxy were investigated. It is shown that the formation of the laterally coupled conglomerates of quantum dots are possible in upper rows for certain parameters of growth, with the corresponding photoluminescence emission being in the wavelength range of 1.3-1.4 µm at room temperature. [ABSTRACT FROM AUTHOR]

Light-emitting III–N heterostructures are grown by gas-phase epitaxy from organometallic compounds on SiC/Si (111) templates (substrates) formed using matched atomic substitution. Investigations of the optical and structural properties of heterostructures are carried out in order to reveal the formation of defects in the structures. It is shown that such heterostructures exhibit specific features of the growth of the (Al,Ga)N buffer layer associated with the presence of pores in Si under the SiC/Si interface. The use of an optimized buffer layer design makes it possible to significantly reduce the dislocation density and form an active region with good structural quality. [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]

The behavior of threading dislocations in AlGaN and InGaN layers incorporated into GaN-based heterostructures is studied. It is shown that InGaN layers with an intermediate composition can be used as the most effective dislocation filters. Estimations of the stresses generated by dislocations and nanodomains show good agreement between the theory and experiment. [ABSTRACT FROM AUTHOR]

AlGaN/AlN/GaN and InAlN/AlN/GaN structures with 2D electron gas have been grown on sapphire substrates by metal-organic vapor-phase epitaxy. The suppression of the parasitic conductivity of buffer GaN layers was provided either by intentionally raising the density of edge dislocations or by doping with iron (GaN:Fe). It was shown that using GaN buffer layers with a better crystal perfection and more planar surface results in the electron mobility in the 2D channel for carriers becoming 1.2-1.5 times higher. [ABSTRACT FROM AUTHOR]

The results of the study of structural and optical properties of short-period InGaN/GaN superlattices synthesized by MOCVD on sapphire substrates are presented. To form the superlattices, the method of periodic interruption of the growth of the InGaN layer with hydrogen supply into the reactor was used. It is shown that, with the use of the suggested method, an InGaN/GaN periodic structure with the developed interfaces and regions of joining the neighboring InGaN layers not correlated in a vertical direction is formed. The formation of such regions leads to a heavy dependence of the shape of the emission spectra of the super-lattices on the number of periods in the range of 400–470 nm. [ABSTRACT FROM AUTHOR]

Structures with InGaN nanolayers within GaN and AlGaN matrices, which constitute active regions of light-emitting devices, have been studied. Spectra and relative intensities of photoluminescence (PL) in the temperature range 20–300 K and the dependence of the position of the PL peak on the energy of the excitation photons have been measured. It is shown that, to account for the temperature dependence of the PL intensity, it is necessary to take into consideration, in addition to the nonradiative recombination via defects in the matrix and in the residual quantum well (RQW), an additional recombination channel with low activation energy, which is presumably associated with defects located close to quantum dots. It is demonstrated that structures with the AlGaN matrix show a larger decrease in the PL intensity upon an increase in temperature from 50 to ∼200 K, compared with structures with the GaN matrix. Analysis of the temperature dependence of the PL intensity in terms of the model that considers these three channels of nonradiative recombination shows that this dependence is associated with a decrease in the carrier’s localization energy relative to the ground state in the RQW. Such a decrease is due to suppression of the phase separation in InGaN layers grown within the AlGaN matrix. This behavior is confirmed by PL measurements at different excitation photon’s energies and leads, in addition to the lower localization energy, a decrease in the concentration of recombination centers is observed for these samples. [ABSTRACT FROM AUTHOR]

We have studied the pyrolysis of trimethylaluminum (TMA) in a nitrogen-containing atmosphere of a vapor phase epitaxy reactor. It is established that, in the presence of gallium nitride coatings in the reactor, the main product of TMA pyrolysis in a nitrogen-hydrogen atmosphere is aluminum nitride. Using this process (without introducing ammonia), we obtained perfect epitaxial aluminum nitride layers. [ABSTRACT FROM AUTHOR]

InGaN quantum dot (QD) formation in a wide pressure range MOCVD reactor was studied. The existence of QDs and their lateral size (2–5 nm) were demonstrated using transmission electron microscopy and high spatial resolution (~ 100 nm) near-field magneto-photoluminescence spectroscopy. We found that an increase of the reactor pressure from 400 to 1000 mbar leads to an order of magnitude increase in light emission efficiency of the InGaN/GaN QDs accompanied by ~ 100 meV redshift of the emission wavelength. We explored stimulated phase separation (SPS) to control carrier localization and emission wavelength. The SPS was achieved by adding In in the matrix material. This leads to formation of extremely deep InGaN/InGaN QDs having energy localization up to ~ 0.8 eV, which was revealed from selectively excited far-field photoluminescence (PL) spectra. Without SPS the QD activation energy is found to be below 0.2 eV. A nonequilibrium carrier population strongly suppresses the temperature-induced shift of the PL emission in deep InGaN QDs. [ABSTRACT FROM AUTHOR]

Electronic and optical properties of ensembles of quantum dots with various energies of activation from the ground-state level to the continuous-spectrum region were studied theoretically and experimentally with the InGaN quantum dots as an example. It is shown that, depending on the activation energy, both the quasi-equilibrium statistic of charge carriers at the levels of quantum dots and nonequilibrium statistic at room temperature are possible. In the latter case, the position of the maximum in the emission spectrum is governed by the value of the demarcation transition: the quantum dots with the transition energy higher than this value feature the quasi-equilibrium population of charge carriers, while the quantum dots with the transition energy lower than the demarcation-transition energy feature the nonequilibrium population. A model based on kinetic equations was used in the theoretical analysis. The key parameters determining the statistic are the parameters of thermal ejection of charge carriers; these parameters depend exponentially on the activation energy. It is shown experimentally that the use of stimulated phase decomposition makes it possible to appreciably increase the activation energy. In this case, the thermal-activation time is found to be much longer than the recombination time for an electron-hole pair, which suppresses the redistribution of charge carriers between the quantum dots and gives rise to the nonequilibrium population. The effect of nonequilibrium population on the luminescent properties of the structures with quantum dots is studied in detail. [ABSTRACT FROM AUTHOR]

GaN-based structures with InGaN quantum dots in the active region, which emit in the blue and green spectral ranges, are studied. The structures grown by both the conventional method and with the use of special procedures of the growth of the active region were compared. The use of these special growth modes stimulates the activated phase decomposition, which leads to the formation of quantum dots with substantially larger localization depth of electrons. It is shown that the formation of such deep quantum dots, like the formation of larger inhomogeneities of the active region, substantially suppresses the lateral carrier transport. This effect improves the characteristics of light-emitting diode structures at a low injection level and increases the temperature stability of quantum efficiency. [ABSTRACT FROM AUTHOR]

Structures with InGaN/GaN quantum dots have been studied using photocurrent spectroscopy. The dynamic range of measurements is found to amount to four orders of magnitude under preservation of the signal-to-noise ratio at a level higher than ten. Within the experimental accuracy, the shape of the spectrum is independent of an applied reverse external bias, whereas the spectrum itself shifts to shorter wavelengths, which is attributed to the Franz–Keldysh effect. Variation of the temperature brings about a change in the spectrum shape. This effect is found to be different for structures grown under different conditions. This behavior can be attributed to homogeneous broadening of the electronic states, the statistics of charge carriers at the levels of quantum dots, and the effect of temperature on the position of these levels. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Under study is the photoluminescence of two types of MBE-grown heterostructures with quantum-confined InGaAsN/GaAs layers: (1) conventional InGaAsN quantum wells (QWs) in GaAs, and (2) heterostructures with an active region consisting of a short-period GaAsN/InGaAsN superlattice that has an InGaAsN QW with a submonolayer InAs insertion at its center. At room temperature, the structures under study emit light in the range from ∼1.3 to ∼1.55μm. In the second type of heterostructure, emission with a wavelength larger than 1.5μm can be obtained at lower nitrogen and indium concentrations than in a conventional QW. This leads to a significant depression of the effects related to decomposition of an InGaAsN solid solution, thus improving the radiative efficiency of the InGaAsN QWs. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The carrier statistics in LED structures with ultrathin multilayer InGaN insertions in a GaN matrix was studied. The optical data obtained indicate that an array of quantum dots (QDs) is formed in these structures. The QDs are scattered in size, which leads to an inhomogeneous broadening of the energy spectrum of carriers localized in the QDs. It is shown that, despite the suppressed transport of carriers between QDs, carriers are distributed among the levels of the QD array quasi-statistically at temperatures of about room temperature and higher. This makes it possible to describe the carrier injection and recombination in the device structures studied in terms of quasi-Fermi levels for electrons and holes. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The electrical and optical properties of light-emitting devices with an active region containing several layers of InGaN/GaN quantum dots (QDs) separated by GaN spacers are studied. It is shown that the overgrowth of the QD layer with an InGaN layer that has a reduced In content at higher temperatures raises the confinement energy of carriers in QDs. Furthermore, inhomogeneous carrier injection, predominantly into regions with higher confinement energy, is observed. The electrical and optical properties of p–n junctions and the effect of the inhomogeneities on these properties are studied in detail. It is shown that the shifts of photoluminescence and electroluminescence lines, which are observed when changing the experimental conditions, are related to these properties of the inhomogeneities in the p–n junction. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Optical properties of MBE-grown ultrathin GaAsN insertions in a GaAs matrix have been studied, with the goal of deriving methods for the intentional formation of carrier localization regions in GaAsN layers. In the case of a short-period GaAs/GaAsN superlattice, an additional long-wavelength line is observed in the photoluminescence spectrum. Comparison of the optical data with the transmission electron microscopy data shows that this line is related to the emission from the formed regions enriched with nitrogen (up to 8.5%). The characteristic size of these nitrogen-enriched regions in upper layers of the superlattice is larger than in lower ones, and it increases with the number of the deposited layers increasing. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The dependence of properties of quantum dot (QD) arrays in an InAs/GaAs system on the InAs growth rate has been investigated theoretically and experimentally. The derived kinetic model of the formation of coherent nanoislands allows the calculation of the average size, surface density of islands, and wetting layer thickness as functions of the growth time and conditions. Optical properties of InAs/GaAs QDs have been studied for the case of two monolayers (ML) of the material deposited at different growth rates. Predictions of the theoretical model are compared with the experimental data. It is shown that with two ML of the deposited material the characteristic lateral size of QDs decreases and the thickness of the residual wetting layer increases with rising growth rate. [ABSTRACT FROM AUTHOR]

Structural and optical properties of InAs quantum dots (QDs) grown in a wide-bandgap (Al[SUB0.3]Ga[SUB0.7]As matrix is studied. It is shown that a high temperature stability of optical properties can be achieved) owing to deep localization of carriers in a matrix whose band gap is wider than that in GaAs. Specific features of QD formation were studied for different amounts of deposited InAs. A steady red shift of the QD emission peak as far as ∼1.18μm with the effective thickness of InAs in Al[SUB0.3]Ga[SUB0.7]As increasing was observed at room temperature. This made it possible to achieve a much higher energy of exciton localization than for QDs in a GaAs matrix. To obtain the maximum localization energy, the QD sheet was overgrown with an InGaAs layer. The possibility of reaching the emission wavelength of ∼1.3μm is demonstrated. [ABSTRACT FROM AUTHOR]

InAs/InGaAsN quantum dots have been grown by molecular beam epitaxy on GaAs substrates. Transmission electron microscopy shows the increase in the island size as compared to the InAs/InGaAs quantum dots. Room temperature photoluminescence at 1.55 μm has been demonstrated whose intensity was comparable to that of the InGaAsN/GaAs quantum wells emitting at 1.3 μm. The effect of nitrogen concentration on the PL peak position and intensity has been studied. [Copyright &y& Elsevier]

Diode lasers based on several layers of self-organized quantum dots (QD) on GaAs substrates were studied. The lasing wavelength lies in the range λ = 1.25-1.29 μm, depending on the number of QD layers and optical losses. A record external differential efficiency of 88% and the characteristic temperature of threshold current, 145 K, were obtained. The internal losses, and also threshold and spectral characteristics, are correlated with the optical gain and radiative recombination efficiency, which are strongly dependent on the design of the active region and growth modes. [ABSTRACT FROM AUTHOR]

The optical properties of GaAsN/GaAs heterostructures grown by molecular-beam epitaxy with different nitrogen content in the layers have been studied. The optical properties of GaAsN layers in the growth conditions under study are defined by the carrier recombination via localized states related to a strong composition inhomogeneity in the solid solution. The increasing of the nitrogen content raises the composition inhomogeneity and the carrier localization energy. [ABSTRACT FROM AUTHOR]

Various structures with optical microcavities and active layers based on InGaAs/GaAs quantum dots MBE-grown on GaAs substrates were studied theoretically and experimentally. LEDs for the 1.3 µm spectral range with narrow spectral characteristics and low light beam divergence were fabricated. Vertical lasing at 1.3 µm was obtained in a structure with oxidized AlO/GaAs mirrors under injection pumping. [ABSTRACT FROM AUTHOR]

A method is proposed for growing stacked InAs/InGaAs self-organized quantum dots on GaAs substrates. The technique allows fabrication of structures exhibiting intense and narrow-line photoluminescence in the 1.3 µm wavelength region. The influence of growth conditions on structural and optical characteristics was studied. The proposed structures show promise in developing vertical-cavity surface-emitting devices. [ABSTRACT FROM AUTHOR]

InGaN/GaN structures with dense arrays of InGaN nanodomains were grown by metallorganic chemical vapor deposition. Lasing in vertical direction occurs at low temperatures, indicating ultrahigh gains (∼10[sup 5] cm[sup -1]) in the active region. Fabrication of an effective AlGaN/GaN distributed Bragg reflector with reflectivity exceeding 90% enables vertical lasing at room temperature in structures with a bottom distributed Bragg reflector, despite the absence of a well-reflecting upper mirror. The lasing wavelength is 401 nm, and the threshold excitation density is 400 kW/cm². [ABSTRACT FROM AUTHOR]

The mechanism for heteroepitaxial growth in the InAs/Si system is studied by reflection highenergy electron diffraction, scanning tunnelling microscopy, and photoluminescence. For certain growth conditions, InAs nanostructures are found to develop on the Si surface immediately during the growth process in the course of molecular beam epitaxy. The range of substrate temperatures that lead to formation of nanosized islands is determined. InAs quantum dots grown on a buffer Si layer with a silicon layer of thickness 50 nm grown on the top produced photoluminescence lines at a wavelength of 1.3 μm at 77 K and 1.6 μm at 300 K. [ABSTRACT FROM AUTHOR]

The feasibility of lasing at a wavelength close to 1.3 µm is demonstrated in InAs quantum-dot structures placed in an external InGaAs/GaAs quantum well. It is shown that the required wavelength can be attained with the proper choice of thickness of the InAs layer deposited to form an array of three-dimensional islands and with a proper choice of mole fraction of InAs in the InGaAs quantum well. Since the gain attained in the ground state is insufficient, lasing is implemented through excited states in the temperature interval from 85 K to 300 K in a structure based on a single layer of quantum dots. The maximum attainable gain in the laser structure can be raised by using three rows of quantum dots, and this configuration, in turn, leads to low-threshold (70 A/cm²) lasing through the ground state at a wavelength of 1.26 µm at room temperature. [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 analytical form of the dependence of the gain on pump current density for lasers with an active region based on self-organized quantum dots is derived in a simple theoretical model. The proposed model is shown to faithfully describe experimental data obtained for laser diodes based on InGaAs quantum dots in an AlGaAs/GaAs matrix, as well as InAs quantum dots in an InGaAs/InP matrix. The previously observed gain saturation and switching of the lasing from the ground state to an excited state of the quantum dots are studied. The influence of the density of quantum-dot arrays on the threshold characteristics of lasers based on them is examined on the basis of this model. [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 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]

Lasing is discovered in the direction perpendicular to the surface in quantum-size InGaN/GaN multilayer heterostructures grown by vapor-phase epitaxy. At high excitation densities one of the modes in the luminescence spectrum, which is modulated by modes of the Fabry-Pérot cavity formed by the GaN/air and GaN/sapphire-substrate interfaces, is sharply amplified and begins to dominate the spectrum. The dependence of the luminescence intensity on pump density has a clearly expressed threshold character. The threshold excitation density in the vertical direction is 5-6 times greater than the stimulated-emission threshold for observation from an end surface of the structure. The gain coefficient in the active region at the threshold for surface-emitting lasing is estimated as 2 × 10[sup 5] cm[sup -1]. The interaction between the cavity modes and the gain spectrum is detected in the form of displacement (by up to 2.6 nm) of modes on the short-wavelength edge of the luminescence spectrum toward higher photon energies. The characteristic temperature (T[sub 0]) measured in the range from 16 to 120 K is 480 K. At higher temperatures T[sub 0] = 70 K. [ABSTRACT FROM AUTHOR]

Capacitance-voltage measurements are used to obtain profiles of the free carrier distribution in Schottky barriers grown on uniformly doped n-GaAs hosts containing layers of selforganized InAs quantum dots. It is found that electrons accumulate at a depth of 0.54 µm, which corresponds to the depth of the quantum-dot layer. As the temperature drops below 90 K, a second peak appears in the concentration profile at 0.61 µm, which becomes dominant as the temperature continues to decrease. It is shown that the appearance of the second peak in the concentration profile is not due to electron density redistribution over the structure, but rather is observed when the rate of thermal emission of electrons from the quantum dots is slower than the angular frequency of the capacitance measurement signal. [ABSTRACT FROM AUTHOR]