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Quantum dots of indium gallium arsenide buried in a thin layer of aluminum gallium arsenide were grown by means of molecular-beam epitaxy. The influence of silver nanoparticles grown on the surface of the semiconductor structure by vacuum thermal evaporation on photoluminescence of quantum dots was investigated. Photoluminescence spectra of quantum dots were obtained under stationary and pulsed excitation. The influence of silver nanoparticles exhibiting plasmon resonances on spectral distribution and kinetics of luminescence of the epitaxial quantum dots was studied.

We study a disorder-induced transformation of the resonant optical reflection from a nearly periodic system of quasi-2D excitons in the InGaN quantum wells arranged as a resonant Bragg structure (RBS). We show that there is a critical deviation from the exact periodicity when the reflection by a single super-radiant exciton–polariton mode is transformed into a multimode spectrum. This critical disorder appears to be inversely proportional to the number of periods in the RBS. Using a numerical model which describes the experimentally observed optical spectra, we found the critical standard deviation from exact periodicity to be 1.76%, 1.0%, and 0.45% for InGaN-based RBS with 60, 100, and 200 periods, respectively.

Photoluminescence, optical reflectance and electro-reflectance spectroscopies were employed to study an AlGaAs/GaAs multiple-quantum-well based resonant Bragg structure, which was designed to match optical Bragg resonance with the exciton-polariton resonance at the second quantum state in the GaAs quantum wells. The structure with 60 periods of AlGaAs/GaAs quantum wells was grown on a semi-insulating substrate by molecular beam epitaxy. Broad and enhanced optical and electro-reflectance features were observed when the Bragg resonance was tuned to the second quantum state of the GaAs quantum well excitons manifesting an enhancement of the light-matter interaction under double-resonance conditions. By applying an alternating electric field, we revealed electro-reflectance features related to the x(e2-hh2) and x(e2-hh1) excitons. The excitonic transition x(e2-hh1), which is prohibited at zero electric field, was allowed by a DC bias due to brake of symmetry and increased overlap of the electron and hole wave functions caused by electric field.

The optical reflection from periodic structures based on a semiconductor AlGaAs matrix containing 2D arrays of plasmonic AsSb nanoinclusions is studied. The number of nanoinclusion layers is 12 or 24, and the nominal spatial periods are 100 or 110 nm, respectively. In the experimental spectra of the optical reflection coefficient at normal incidence, we observe resonant Bragg diffraction with the main peaks at wavelengths of 757 or 775 nm (1.64 or 1.60 eV), depending on the spatial period of the nanostructure. The magnitudes of the resonance peaks reach 22 and 31% for the systems of 12 and 24 AsSb–AlGaAs layers, while the volume fraction of the nanoinclusions is much less than 1%. In the case of light incident at inclined angles, the Bragg-diffraction pattern shifts according to Wulff–Bragg’s law. Numerical simulation of the optical reflection spectra is performed using the transfer-matrix method by taking into account the spatial geometry of the structures and the resonance characteristics of the plasmonic AsSb layers.

The optical reflectance and transmittance spectra of a periodic InGaN/GaN semiconductor heterostructure with 60 quantum wells are studied at room temperature. The period of the structure was chosen such that, at some angles of incidence of light, the energy of a photon resonantly reflected from the Bragg structure coincides with the excitation energy for quantum-well excitons in quantum wells. The parameters of these excitons are determined by fitting the spectra measured at two different angles of incidence, 30° and 60°. We take into account the resonant exciton transitions in quantum wells as well as the transitions into the continuous spectrum. The radiative decay parameter is determined to be (0.20 ± 0.02) meV.

The photoluminescence of InAs semiconductor quantum dots overgrown by GaAs in the low-temperature mode (LT-GaAs) using various spacer layers or without them is studied. Spacer layers are thin GaAs or AlAs layers grown at temperatures normal for molecular-beam epitaxy (MBE). Direct overgrowth leads to photoluminescence disappearance. When using a thin GaAs spacer layer, the photoluminescence from InAs quantum dots is partially recovered; however, its intensity appears lower by two orders of magnitude than in the reference sample in which the quantum-dot array is overgrown at normal temperature. The use of wider-gap AlAs as a spacer-layer material leads to the enhancement of photoluminescence from InAs quantum dots, but it is still more than ten times lower than that of reference-sample emission. A model taking into account carrier generation by light, diffusion and tunneling from quantum dots to the LT-GaAs layer is constructed.

Localization of carriers in a self-organized quantum dot is a problem of quantum mechanics to be solved with the localizing potential for electrons and holes determined by the geometry, chemical composition, and built-in mechanical stress–strain field. We show that changes in the aspect ratio of a buried pyramidal quantum dot result in a substantial redistribution of the mechanical field components, which in turn provides certain non-trivial conditions for the strongest carrier localization at any given volume of the quantum dot.

Optical extinction in a metal–semiconductor metamaterial based on a AlGaAs matrix, which contains random arrays of AsSb plasmon nanoinclusions, is studied. The metamaterial is grown by molecular beam epitaxy at a low temperature. A system of nanoinclusions of various sizes is formed by annealing at temperatures 400, 500, and 600°C. Investigation of the sample’s microstructure by transmission electron microscopy shows that the average size of nanoinclusions at the used annealing temperatures is 4–7, 5–8, and 6–9 nm, respectively. It is shown experimentally that AsSb nanoparticle arrays in the AlGaAs matrix cause the resonant absorption of light. It is established that the plasmon-resonance parameters found in the metamaterial are almost independent of the sizes of the AsSb nanoinclusions. The plasmon-resonance energy is (1.47 ± 0.01) eV, while its full width at half maximum is (0.19 ± 0.01) eV.

A single molecular-beam epitaxy process is used to produce GaAs-based heterostructures containing two-dimensional arrays of InAs semiconductor quantum dots and AsSb metal quantum dots. The twodimensional array of AsSb metal quantum dots is formed by low-temperature epitaxy which provides a large excess of arsenic in the epitaxial GaAs layer. During the growth of subsequent layers at a higher temperature, excess arsenic forms nanoinclusions, i.e., metal quantum dots in the GaAs matrix. The two-dimensional array of such metal quantum dots is created by the δ doping of a low-temperature GaAs layer with antimony which serves as a precursor for the heterogeneous nucleation of metal quantum dots and accumulates in them with the formation of AsSb metal alloy. The two-dimensional array of InAs semiconductor quantum dots is formed via the Stranski–Krastanov mechanism at the GaAs surface. Between the arrays of metal and semiconductor quantum dots, a 3-nm-thick AlAs barrier layer is grown. The total spacing between the arrays of metal and semiconductor quantum dots is 10 nm. Electron microscopy of the structure shows that the arrangement of metal quantum dots and semiconductor quantum dots in the two-dimensional arrays is spatially correlated. The spatial correlation is apparently caused by elastic strain and stress fields produced by both AsSb metal and InAs semiconductor quantum dots in the GaAs matrix.

We study the coherent dynamics of localized excitons in 100-periods of 2.5 nm thick (In,Ga)N/GaN quantum wells with 7.5% indium concentration, measured with spectroscopic resolution through two-pulse and three-pulse photon echoes at the temperature of 1.5 K. A long-lived coherent exciton dynamics is observed in the (In,Ga)N quantum wells: When the laser photon energy is tuned across the 43 meV-wide inhomogeneously broadened resonance line, the coherence time T2 varies between 45 and 255 ps, increasing with stronger exciton localization. The corresponding narrow homogeneous linewidths ranging from 5.2 to 29 {\mu}eV as well as the relatively weak exciton-phonon interaction (0.8 {\mu}eV/K) confirm a strong, quantum dot-like exciton localization in a static disordered potential inside the (In,Ga)N quantum well layers., Comment: 4 figs

Optical lattices of excitons in periodic systems of InGaN quantum wells with GaN barriers are designed, implemented, and investigated. Due to the collective interaction of quasi-two-dimensional excitons with light and a fairly high binding energy of excitons in GaN, optical Bragg reflection at room temperature is significantly enhanced. To increase the resonance optical response of the system, new structures with two quantum wells in a periodic supercell are designed and implemented. Resonance reflection of 40% at room temperatures for structures with 60 periods is demonstrated.

Electron-microscopy studies of GaAs structures grown by the method of molecular-beam epitaxy and containing arrays of semiconductor InAs quantum dots and metallic As quantum dots are performed. An array of InAs quantum dots is formed using the Stranski-Krastanow mechanism and consists of five layers of vertically conjugated quantum dots divided by a 5-nm-thick GaAs spacer layer. The array of As quantum dots is formed in an As-enriched GaAs layer grown at a low temperature above an array of InAs quantum dots using postgrowth annealing at temperatures of 400–600°C for 15 min. It is found that, during the course of structure growth near the InAs quantum dots, misfit defects are formed; these defects are represented by 60° or edge dislocations located in the heterointerface plane of the semiconductor quantum dots and penetrating to the surface through a layer of “low-temperature” GaAs. The presence of such structural defects leads to the formation of As quantum dots in the vicinity of the middle of the InAs conjugated quantum dots beyond the layer of “low-temperature” GaAs.

A stack of five layers of epitaxial InAs QDs with GaAs barriers was grown by molecular-beam epitaxy. The upper layer of QDs was capped by 3nm-GaAs/3nm-AlAs/4nm-GaAs layer sequence. Then, a thin silver layer was added via physical vapor deposition. After annealing isolated silver nanoparticles were formed above the layer of buried InAs quantum dots. We studied interplay of the exciton resonance in InAs QDs and plasmon resonance in Ag nanoparticles. In particular, we observed more than twofold enhancement of the exciton photoluminescence intensity from the InAs QDs when they were coupled to the silver nanoparticles.

The optical absorption in a metal-semiconductor metamaterial based on the AlGaAs matrix has been investigated. The key feature of this material is the presence of random arrays of metallic AsSb nanoinclusions modifying its dielectric properties. It has been shown that the presence of such arrays in the material leads to resonance absorption of light by surface plasmons in AsSb nanoinclusions in the incident photon energy range from 1.37 to 1.77 eV. The experimental spectrum of the extinction coefficient at an energy of 1.48 eV exhibits a resonance peak with the half-width equal to 0.18 eV. The extinction coefficient for AsSb nanoinclusions in the AlGaAs matrix has been calculated in terms of the Mie theory. The calculated spectrum of the extinction coefficient also includes a resonance peak with the energy and half-width equal to 1.48 and 0.18 eV, respectively. The calculated plasma energy for free-standing nanoinclusions in vacuum is 7.38 eV.

The effect of exciton-polariton resonance on the optical properties of periodic heterostructures with double InGaN quantum wells in a GaN matrix has been studied. It has been found that the light reflection is amplified at the frequency corresponding to the exciton energy when it coincides with the frequency of the Bragg resonance. This effect is observed to be twice as large as that in a similar system of single quantum wells.

Electron microscopy studies of GaAs-based structures grown by molecular beam epitaxy and containing arrays of semiconductor InAs quantum dots and metal As quantum dots are performed. The array of InAs quantum dots is formed by the Stranski-Krastanov mechanism and consists of vertically coupled pairs of quantum dots separated by a GaAs spacer 10 nm thick. To separate the arrays of semiconductor and metal quantum dots and to prevent diffusion-induced mixing, the array of InAs quantum dots is overgrown with an AlAs barrier layer 5 or 10 nm thick, after which a GaAs layer is grown at a comparatively low temperature (180°C). The array of As quantum dots is formed in an As-enriched layer of the low-temperature GaAs by means of post-growth annealing at 400–760°C for 15 min. It is established that the AlAs barrier layer has a surface profile corresponding to that of a subbarrier layer with InAs quantum dots. The presence of such a profile causes the formation of V-shaped structural defects upon subsequent overgrowth with the GaAs layer. Besides, it was obtained that AlAs layer is thinned over the InAs quantum dots tops. It is shown that the AlAs barrier layer in the regions between the InAs quantum dots effectively prevents the starting diffusion of excess As at annealing temperatures up to 600°C. However, the concentration of mechanical stresses and the reduced thickness of the AlAs barrier layer near the tops of the InAs quantum dots lead to local barrier breakthroughs and the diffusion of As quantum dots into the region of coupled pairs of InAs quantum dots at higher annealing temperatures.

The optical properties of metal-semiconductor metamaterials based on an AlGaAs matrix are studied. The specific feature of these materials is that there are As and AsSb nanoinclusion arrays which modify the dielectric properties of the material. These nanoinclusions are randomly arranged in the medium or form a Bragg structure with a reflectance peak at a wavelength close to 750 nm, corresponding to the transparency region of the matrix. The reflectance spectra are studied for s- and p-polarized light at different angles of incidence. It is shown that (i) As nanoinclusion arrays only slightly influence the optical properties of the medium in the wavelength range 700–900 nm, (ii) chaotic AsSb nanoinclusion arrays cause strong scattering of light, and (iii) the spatial periodicity in the arrangement of AsSb nanoinclusions is responsible for Bragg resonance in the optical reflection.

GaAs samples grown by molecular-beam epitaxy at low (230°C) temperatures are investigated. One of the samples is subjected to aftergrowth annealing at 600°C. Using an unconventional pump-probe scheme for measuring the dynamic variation in the light refractive index, the nonequilibrium charge-carrier lifetime (275 ± 30 fs before annealing) is determined. Such a short carrier lifetime in the unannealed material is due to the high concentration of point defects, mainly AsGa antisite defects. According to X-ray diffraction and steady-state optical absorption data, the AsGa concentration in the samples is 3 × 1019 cm−3, which corresponds to an arsenic excess of 0.26 at %. Upon annealing at 600°C, the superstoichiometric As defects self-organize and form As nanoinclusions in the GaAs crystal matrix. It is shown that in this case the nonequilibrium charge-carrier lifetime increases to 452 ± 5 fs. This lifetime is apparently ensured by the capture of non-equilibrium charge carriers at metal As nanoinclusions.

The optical reflectance and transmittance of GaAs structures grown by molecular-beam epitaxy at a low temperature and periodically δ-doped with antimony or phosphorus are studied. The periodicity of the doping corresponded to the Bragg condition for light with a free-space wavelength of ∼1.4 μm. The structures were subjected to annealing at different temperatures in the range from 400 to 760°C. Annealing brings about the formation of a three-dimensional chaotic system of As metal nanoinclusions (quantum dots) inside the GaAs epitaxial layer as well as the formation of two-dimensional layers of AsSb metal nanoinclusions (quantum dots) on the Sb δ layers. The P δ layers have no significant effect on the formation of the system of As nanoinclusions. No features that might be attributed to a disordered three-dimensional system of As nanoinclusions are detected in the optical transmittance and reflectance spectra. The periodic system of two-dimensional layers of AsSb metal nanoinclusions manifests itself as a resonance peak in the optical reflectance and absorption spectra. The resonance reflectance and absorption coefficient increase, as the dimensions of the AsSb nanoinclusions increase. The resonance wavelength depends on the angle of light incidence in accordance with Bragg’s law.

The optical reflection spectra of periodic structures with two quantum wells in the unit cell are investigated. The dependences of the features of Bragg reflection and exciton-polariton reflection on the angle of incidence and polarization of light and the sample temperature are studied. Analysis of the experimental data shows that a 60-period structure acts as a distributed Bragg reflector with a peak reflectivity exceeding 90% and a spectral band width as large as 16 meV.

Elastic fields in a system consisting of a surface coherent axisymmetric quantum dot-island on a massive substrate have been theoretically studied using the finite element method. An analysis of the influence of the quantum dot shape (form factor) and relative size (aspect ratio) δ on the accompanying elastic fields has revealed two critical quantum dot dimensions, δc1 and δc2. For δ > δc1, the fields are independent of the quantum dot shape and aspect ratio. At δ ≥ δc2, the quantum dot top remains almost undistorted. Variation of the stress tensor component σzz (z is the quantum dot axis of symmetry) reveals a region of tensile stresses, which is located in the substrate under the quantum dot at a particular distance from the interface. Using an approximate analytical formula for the radial component of displacements, model electron microscopy images have been calculated for quantum dot islands with δ > δc1 in the InSb/InAs system. The possibility of stress relaxation occurring in the system via the formation of a prismatic interstitial dislocation loop has been considered.

Peculiarities of the measurement of femtosecond lifetimes of free charge carriers in gallium arsenide grown by the method of molecular beam epitaxy are considered. The carrier lifetime is determined by a variant of the pump-probe method in which the pumping and probing radiation beams are incident onto the semiconductor sample surface at the Brewster angle. The proposed variant ensures the detection of a change in the induced refractive index even in the case of very small response signals, thus providing for a high sensitivity of measurements. It is shown that the relative signal changes near the Brewster angle reach a maximum level.

Photoluminescence and optical-reflection spectra of a periodic structure consisting of 60 tunneling-isolated GaAs quantum wells separated by AlGaAs barriers are studied. The structure is designed so that, for a certain angle of incidence (∼23°), the Bragg resonance condition is satisfied for light with a photon energy equal to the energy of heavy-hole excitons at the second quantum-confinement level in the wells. It is established experimentally that, under the conditions of double exciton-polariton and Bragg resonance, a superradiant optical mode is formed. Dependences of Bragg and exciton-polariton reflection on the angle of incidence and polarization of light and the temperature are investigated.

Epitaxial GaAs layers containing InAs semiconductor quantum dots and As metal quantum dots are grown by molecular beam epitaxy. The InAs quantum dots are formed by the Stranskii-Krastanow mechanism, whereas the As quantum dots are self-assembled in the GaAs layer grown at low temperature with a large As excess. The microstructure of the samples is studied by transmission electron microscopy. It is established that the As metal quantum dots formed in the immediate vicinity of the InAs semiconductor quantum dots are larger in size than the As quantum dots formed far from the InAs quantum dots. This is apparently due to the effect of strain fields of the InAs quantum dots upon the self-assembling of As quantum dots. Another phenomenon apparently associated with local strains around the InAs quantum dots is the formation of V-like defects (stacking faults) during the overgrowth of the InAs quantum dots with the GaAs layer by low-temperature molecular beam epitaxy. Such defects have a profound effect on the self-assembling of As quantum dots. Specifically, on high-temperature annealing needed for the formation of large-sized As quantum dots by Ostwald ripening, the V-like defects bring about the dissolution of the As quantum dots in the vicinity of the defects. In this case, excess arsenic most probably diffuses towards the open surface of the sample via the channels of accelerated diffusion in the planes of stacking faults.

The structure of low-temperature grown superlattices of GaAs with delta-layers of Sb and P was studied by analysis of the X-ray diffraction curves, which was accompanied by optical absorption measurements and transmission electron microscopy. The obtained structural parameters included the periods of structure, thicknesses of the Sb and P δ-layers, amount of excess As in the as-grown state. Variations of these parameters were documented when samples were annealed and the excess As transformed from antisite defects into As nanoinclusions.

Evidence given by electron microscopy of dislocation relaxation of stresses near InAs quantum dots buried into GaAs is presented. It was found that dislocation defects not emerging to the film surface are formed in some buried quantum dots. This suggests that stress relaxation occurs in the buried state of the quantum dot, rather than at the stage of the formation and growth of an InAs island on the GaAs surface. Models of internal dislocation relaxation of buried quantum dots are presented.

High-resolution X-ray diffractometry is used to study the GaAs structures grown at a low temperature (LT-GaAs) by molecular beam epitaxy. The feature of the studied structures is the presence of thin (about 1 monolayer) layers δ-doped with isovalent Sb and P impurities and formed at a low epitaxial temperature. The δ-doped layers periodically arranged in the bulk of the epitaxial film form the X-ray diffraction pattern containing a large number of interference peaks, whose quantitative analysis allows one to extract the information on the thickness, chemical composition, and abruptness of layer boundaries. Such an analysis was performed before and after annealing of the studied samples, and this annealing gives rise to a system of As nanoinclusions (quantum dots) in the bulk of the epitaxial film. The variations in the parameters of diffraction curves that characterize the process of formation of the As quantum dots are revealed. It is established that the formation of the system of As quantum dots in LT-GaAs (δ-Sb) causes enhanced damping of super-lattice satellite peaks, which is probably associated with an increase in the roughness and diffusion spreading of the layers δ-doped with Sb. A similar phenomenon was not observed in LT-GaAs (δ-P), which is most probably caused by the absence of heterogeneous precipitation of As in the layers δ-doped with P and lower effective coefficients of diffusion intermixing As-P compared with As-Sb. For the samples with a combined system of the layers δ-doped with Sb and P, the diffraction curves quantitatively confirmed the formation of superlattices containing the system of As quantum dots, in which the mismatch with respect to the GaAs substrate by the average lattice parameter is less than 0.0001%.

Contactless optical electroreflectance measurements at different temperatures are used to study exciton states in a structure involving a periodic system of 36 GaAs quantum wells separated by tunneling-nontransparent AlGaAs barriers with thickness 104 nm. In the structure, the width of 32 of the quantum wells is 15 nm, while the width of the remaining four quantum wells, numbered 5, 14, 23, and 32, is 20 nm. The periodicity of the structure corresponds to the Bragg interference condition at the excitonic frequency in quantum wells at the angle of incidence of light ∼43°. From the quantitative analysis of the shape of the contactless electroreflectance line, the parameters of the exciton ground states and excited states are determined for both types of quantum wells. It is established that, for the system of four 20-nm-wide quantum wells separated by a distance of 830 nm, the size-quantization energy in the ground state is 8.4 ± 0.1 meV, and the parameter of broadening of the excitonic peak is 1.8 ± 0.1 meV at 17 K and increases with temperature up to 2.0 ± 0.1 meV at 80 K. For the system of 32 wells with the width 15 nm, the quantum confinement energy in the ground state is 14.9 ± 0.1 meV, and the parameter of broadening of the excitonic peak is 2.2 ± 0.1 and 2.6 ± 0.1 meV at 17 and 80 K, respectively. The possible causes of radiative and nonradiative broadening of exciton states in the systems are discussed.

We studied optical reflection (OR) and contactless electroreflection (CER) from a periodic system of multiple GaAs/AlGaAs quantum wells (QWs). The QW width was 15 or 20 nm and the barriers were 104 nm thick. In this system the electromagnetic resonance of Bragg reflection occurs at the frequency that coincides or is close to the frequency of the exciton–polariton resonance in the wells. The optical measurements were made at various temperatures, angles of the light incidence and polarization. The optical reflection spectra have been found to be a result of the interplay of three different contributions, namely (i) the reflection from the air/semiconductor interface, (ii) the Bragg reflection due to periodic modulation of the background indices of refraction being different for the wells and barriers and (iii) the resonant reflection from the periodic system of exciton–polaritons in quantum wells. The latter contribution was separately studied by CER technique in the spectral range covering ground states of the heavy-hole and light-hole excitons. A quantitative analysis of the experimental CER line shape has been done along with quantum-mechanical calculations, which revealed the characteristic energies and broadening parameters for different exciton–polariton levels. In particular, the systems of four and 32 QWs exhibit spectral features with the characteristic broadening of 1.8 meV and 2.2 meV at 17 K, respectively. By comparison with theoretical calculations we discuss the radiative and non-radiative contributions to the total broadening.

Optical reflection and electroreflection for the AlGaAs layers containing the periodically arranged GaAs quantum wells of different thickness are studied at photon energies ranging from 1 to 2 eV. It is established that the spectral dependence of the reflectance involves three different contributions made by (i) the reflection from the medium-air interface; (ii) the interference reflection due to the periodically modulated refractive index, since the materials of the wells and barriers have different refractive indices; and (iii) the reflection produced by the interaction of electromagnetic waves with the excition states in the quantum wells. Analysis of the reflection spectra shows that these contributions are characterized by different behavior with variations in temperature, angle of incidence of light, and polarization; however, quantitative separation of the spectra into individual contributions presents a rather difficult problem. To separate the contribution originating from the interaction of light with the exciton states from the optical spectra, a special approach based on contactless measurements of the optical electroreflectance over a certain spectral region is developed. It is shown that this method provides a means for determining the parameters of the exciton states in the quantum wells.

The problem of defect formation in the GaAs and InGaAs layers grown by low-temperature molecular-beam epitaxy is discussed. The effect of growth conditions (temperature and flux ratio between the elements of groups III and V) on the morphology of growth surface, internal structure, type, and concentration of electrically-and optically active defects is analyzed. A comparison is made between the defect formation processes occuring during the epitaxial growth and post-growth annealing of the layers.

The optical reflectance spectra of resonant Bragg quantum-well structures are studied theoretically. The existence of two special frequencies in the spectra at which the reflectance depends only weakly on the number of quantum wells in the structure is explained analytically. The effect of nonradiative exciton damping on the reflectance spectra in the vicinity of the special frequencies is analyzed. It is shown that the inclusion of the dielectric contrast leads to the appearance of a third special frequency, at which the contributions to the reflectance due to the dielectric contrast and exciton resonance completely cancel each other.

Transmitting electron microscopy and X-ray diffractometry are used to study the GaAs layers undoped or doped uniformly with phosphorus (2.3 mol %) and grown at a temperature of 250°C and then annealed isochronously at 400, 500, 600, or 700°C. It is ascertained that doping with phosphorus reduces the amount of excess arsenic captured in the layer in the course of growth and also brings about a retardation of precipitation during subsequent annealing. The concentration of excess arsenic in undoped samples amounted to ∼0.2 at %; clusters were observed after annealing at a temperature of 500°C. The concentration of excess arsenic amounted to 0.1 at % in the samples containing phosphorus; in this case, the clusters were observed only after a heat treatment at 600°C. The average size of clusters in doped samples is smaller than that in undoped samples at the same heat-treatment temperatures.

International audience; Electron traps in GaAs grown by MBE at temperatures of 200–300°C (LT-GaAs) were studied. Capacitance deep level transient spectroscopy (DLTS) was used to study the Schottky barrier on n-GaAs, whose space-charge region contained a built-in LT-GaAs layer ∼0.1 µm thick. The size of arsenic clusters formed in LT-GaAs on annealing at 580°C depended on the growth temperature. Two new types of electron traps were found in LT-GaAs layers grown at 200°C and containing As clusters 6–8 nm in diameter. The activation energy of thermal electron emission from these traps was 0.47 and 0.59 eV, and their concentration was ∼1017 cm−3, which is comparable with the concentration of As clusters determined by transmission electron microscopy. In LT-GaAs samples that were grown at 300°C and contained no arsenic clusters, the activation energy of traps was 0.61 eV. The interrelation between these electron levels and the system of As clusters and point defects in LT-GaAs is discussed.

A periodic multiple quantum well GaAs/AlGaAs structure was designed, grown and characterized in order to reveal resonant features in optical spectra when the Bragg resonance was tuned to the first or second quantum state of the heavy-hole exciton-polaritons in the quantum wells. We observed a super-radiant optical mode formed by the quantum well excitons under double resonance condition, i.e. when the exciton-polariton and Bragg resonances are met at the same frequency. It is manifested in a strong and wide reflection and electroreflection band (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The relaxation dynamics of nonequilibrium charge carriers in gallium arsenide epitaxial films grown by molecular-beam epitaxy at low temperatures has been studied. The growth conditions of the epitaxial layer provided an excess arsenic content of 1.2% in the layer. In a material of this kind, the carrier lifetime is

Using micro-Raman spectroscopy we have investigated the n dopant and strain distribution in lateral epitaxial overgrowth technique GaN films grown by metalorganic chemical vapor deposition on the sapphire (0001) substrates with SiNx masks. The widths of the mask stripes were 2, 4, 8, or 16 μm, while the mask windows were always 4 μm wide. In the case of narrow stripes (2 and 4 μm), when the overgrowth wings were well coalesced, the films were found to be fairly uniform with a background n doping of (4±2)×1017 cm−3. The GaN wings in the samples with 8 and 12 μm stripes did not coalesce, leaving “V”-shaped and trapezoidal grooves, respectively. In the latter case, additional doping [n=(6.5±0.6)×1017 cm−3] of the wing area was revealed, which may be due to surface diffusion of Si atoms from the SiNx mask to the GaN growth front and their incorporation into the growing film.

The elastic behavior of a spherical inclusion with a uniaxial dilatation is considered. As an example, the experimental data on stressed nanoclusters in doped semiconductors (As-Sb clusters in GaAs) are presented. The fields of displacements, elastic strains, and stresses are determined for spherical inclusions with uniaxial dilatation, and the specific features of these fields are revealed. The elastic energy of a uniaxial spheroid is calculated and compared with that for a triaxial spheroid. The relaxation mechanisms for the elastic field of the inclusion associated with the formation of prismatic dislocation loops are considered.

Using the methods of X-ray diffraction, optical absorption in the near-infrared range, and the Hall effect, the influence of growth conditions on the structure and properties of Si-doped GaAs layers grown by low-temperature molecular-beam epitaxy was investigated. The relation between the incorporation of excess As and electrical properties of the layers is analyzed.

We have investigated the n-dopant distribution in the overgrown and window regions of lateral-epitaxial overgrown GaN/sapphire (0001) using room-temperature micro-Raman spectroscopy in the backscattering configuration. From a fit to the high energy-coupled longitudinal optical (LO) phonon-plasmon mode (LPP+), we have evaluated n ≈ (6.5 ± 0.6) × 1017 cm-3 in the overgrown region; a value considerably higher than that previously reported by Pophristic et al. The spectrum from the window region was harder to interpret because of the considerable overlap of the A1(LO) mode and Eg(750 cm-1) sapphire line with the LPP+ trace. The implications of our findings for the overgrown region on the measured thermal conductivity as well as other parameters will be discussed.

The present paper reviews works devoted to control over the properties of epitaxial GaAs by incorporation of excess (non-stoichiometric) arsenic into the GaAs films grown by molecular-beam epitaxy (MBE) at low-temperature (LT). The effect of excess arsenic on the material structure and properties is analyzed for both as-grown and annealed LT-GaAs layers. The effect of doping on the incorporation of excess arsenic is also examined. The data on the effect of excess arsenic on the properties of the Ga0.47In0.53As solid solution are presented. The specific features of the mechanism of the excess arsenic incorporation into the solid phase during the low-temperature epitaxial growth are discussed.

A nontraditional approach to the control of GaAs properties via the introduction of an excessive amount of arsenic during growth of epitaxial layers under conditions of low-temperature molecular-beam epitaxy (LT-GaAs layers) is considered. The influence of excessive arsenic on the structure and properties of as-grown and annealed LT-GaAs layers is considered as well as the effect of layer doping on the “capture” of excess arsenic.

The optical properties of a hybrid material consisting of semiconductor quantum dots and metallic nanoparticles are investigated. A semiconductor structure containing a stack of five layers of indium arsenide quantum dots near the surface of gallium arsenide is fabricated using molecular beam epitaxy. The surface of the structure is covered by a layer of silver nanoparticles, whose plasmon resonances are close to exciton transitions in quantum dots. The redshift of the extinction spectrum of the quantum dots and enhancement of photoluminescence are observed, indicating the interaction between the resonances in the components of the hybrid system formed here.

An AlGaAs/GaAs multiple-quantum-well based resonant Bragg structure was designed to match the optical Bragg resonance with the exciton-polariton resonance at the second quantum state in the GaAs quantum wells. The sample structure with 60 periods of AlGaAs/GaAs quantum wells was grown on a semi-insulating GaAs substrate by molecular beam epitaxy. Angle- and temperature-dependent photoluminescence, optical reflectance, and electro-reflectance spectroscopies were employed to study the resonant optical properties of the Bragg structure. Broad and enhanced optical and electro-reflectance features were observed when the Bragg resonance was tuned to the second quantum state of the GaAs quantum well excitons, manifesting a strong light-matter interaction. From the electro-optical experiments, we found the electro-reflectance features related to the transitions of x(e2-hh2) and x(e2-hh1) excitons. The excitonic transition x(e2-hh1), which is prohibited at zero electric field, was allowed by a DC bias due to the b...

An electron-microscopy study of GaAs structures, grown by molecular-beam epitaxy, containing two coupled layers of InAs semiconductor quantum dots (QDs) overgrown with a thin buffer GaAs layer and a layer of low-temperature-grown gallium arsenide has been performed. In subsequent annealing, an array of As nanoinclusions (metallic QDs) was formed in the low-temperature-grown GaAs layer. The variation in the microstructure of the samples during temperature and annealing conditions was examined. It was found that, at comparatively low annealing temperatures (400–500°C), the formation of the As metallic QDs array weakly depends on whether InAs semiconductor QDs are present in the preceding layers or not. In this case, the As metallic QDs have a characteristic size of about 2–3 nm upon annealing at 400°C and 4–5 nm upon annealing at 500°C for 15 min. Annealing at 600°C for 15 min in the growth setup leads to a coarsening of the As metallic QDs to 8–9 nm and to the formation of groups of such QDs in the area of the low-temperature-grown GaAs which is directly adjacent to the buffer layer separating the InAs semiconductor QDs. A more prolonged annealing at an elevated temperature (760°C) in an atmosphere of hydrogen causes a further increase in the As metallic QDs’ size to 20–25 nm and their spatial displacement into the region between the coupled InAs semiconductor QDs.

GaAs films δ-doped with phosphorus (one monolayer) were grown by molecular beam epitaxy at a temperature of 200°C (LT-GaAs), isochronally annealed at 400, 500 or 600°C, and studied by transmission electron microscopy. Analysis of the moire fringes in the electron microscopy images of the clusters formed upon annealing revealed that their microstructure and orientation relationship correspond to the parameters of pure As clusters in GaAs; hence, there is no considerable incorporation of phosphorus from the matrix into the forming clusters during precipitation of excess As. Examination of the cluster’s spatial distribution across the LT-GaAs films showed no variation in the cluster array’s concentration near the P °-layers for the used growth and annealing conditions. Thus, phosphorus, being introduced into a LT-GaAs film in the form of °-layers, behaves as the isovalent Al impurity and differs from such isovalent impurities as In and Sb by the effect on the spatial distribution of As clusters.

Low-temperature photoluminescence (PL) studies of gallium-arsenide layers grown by molecular-beam epitaxy at low (200 °C) temperatures (LT GaAs) and doped with silicon or a combination of silicon and indium have been performed. The PL spectra of as-grown samples reveal a shallow acceptor-based line only. After annealing, an additional line at ∼1.2 eV appears, which is attributable to SiGa-V Ga complexes. The activation energy of complex formation is found to be close to the activation energy of migration of gallium vacancies and is equal to 1.9±0.3 eV for LT GaAs: Si. It is found that doping with a combination of silicon and indium leads to an increase in the activation energy of formation of SiGa-V Ga complexes to 2.5±0.3 eV. We believe that this increase in the activation energy is controlled by the gallium vacancy-indium interaction through local lattice deformations.

Capacitance spectroscopy was used to investigate the properties of Au/GaAs Schottky barriers in structures in which a thin layer of gallium arsenide grown at low temperature (LT-GaAs) and containing As clusters was sandwiched between two uniformly copper-doped layers of n-GaAs grown at standard temperatures. We detected electron accumulation in the LT-GaAs layer surrounded by two depletion regions in the adjacent n-GaAs layers. Emission of electrons from the LT-GaAs layer at 300 K results in an extended plateau in the capacitance-voltage characteristic. It is found that the presence of the 0.1 µm thick LT-GaAs layer sandwiched between the two much thicker n-GaAs layers results in an increase in the breakdown electric field to values as high as 230 kV/cm, which is much higher than typical values for standard Au/n-GaAs structures.