Vol 50, No 11 (2016)
- Year: 2016
- Articles: 26
- URL: https://journals.rcsi.science/1063-7826/issue/view/12388
XX International Symposium “Nanophysics and Nanoelectronics”, Nizhny Novgorod, March 14–18, 2016
Hybrid AlGaAs/GaAs/AlGaAs nanowires with a quantum dot grown by molecular beam epitaxy on silicon
Abstract
Data on the growth features and physical properties of GaAs inserts embedded in AlGaAs nanowires grown on Si(111) substrates by Au-assisted molecular beam epitaxy are presented. It is shown that by varying the growth parameters it is possible to form structures like quantum dots emitting in a wide wavelength range for both active and barrier regions. The technology proposed opens up new possibilities for the integration of direct-band III–V materials on silicon.
Modulation of intersubband light absorption and interband photoluminescence in double GaAs/AlGaAs quantum wells under strong lateral electric fields
Abstract
The effect of a lateral electric field on the mid-infrared absorption and interband photoluminescence spectra in double tunnel-coupled GaAs/AlGaAs quantum wells is studied. The results obtained are explained by the redistribution of hot electrons between quantum wells and changes in the space charge in the structure. The hot carrier temperature is determined by analyzing the intersubband light absorption and interband photoluminescence modulation spectra under strong lateral electric fields.
Optical spectroscopy of a resonant Bragg structure with InGaN/GaN quantum wells
Abstract
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.
Stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on GaAs and Ge/Si(001) substrates
Abstract
We report the observation of stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on Si(001) substrates with the application of a relaxed Ge buffer layer. Stimulated emission is observed at 77 K under pulsed optical pumping at a wavelength of 1.11 μm, i.e., in the transparency range of bulk silicon. In similar InGaAs/GaAsSb/GaAs structures grown on GaAs substrates, room-temperature stimulated emission is observed at 1.17 μm. The results obtained are promising for integration of the structures into silicon-based optoelectronics.
Heavily doped GaAs:Te layers grown by MOVPE using diisopropyl telluride as a source
Abstract
The capabilities of GaAs epitaxial layers extremely heavily doped with tellurium by metal-organic vapor-phase epitaxy using diisopropyl telluride as a source are studied. It is shown that tellurium incorporation into GaAs occurs to an atomic concentration of 1021 cm–3 without appreciable diffusion and segregation effects. Good carrier concentrations (2 × 1019 cm–3) and specific contact resistances of non-alloyed ohmic contacts (1.7 × 10–6 Ω cm2) give grounds to use such layers to create non-alloyed ohmic contacts in electronic devices. A sharp decrease in the electrical activity of Te atoms, a decrease in the electron mobility, and an increase in the contact resistance at atomic concentrations above 2 × 1020 cm–3 are detected.
Fabrication of MnGa/GaAs contacts for optoelectronics and spintronics applications
Abstract
The crystal structure, composition, and magnetic, and electric-transport properties of MnxGay layers deposited onto a GaAs surface by pulsed laser deposition in a hydrogen atmosphere, pulsed laser deposition in vacuum, and electron-beam evaporation in vacuum are investigated. It is shown that the features of each technique affect the composition and crystal structure of the formed layers, and the degree of abruptness and crystalline quality of the heterointerface. Apparently, the composition and crystal structure are responsible for modification of the ferromagnetic properties. The defects in the heterointerface affect the properties of the MnxGay/GaAs diode structure, in particular, the height of the Schottky diode potential barrier.
Germanium laser with a hybrid surface plasmon mode
Abstract
The possibility of creating an n++-Ge laser with a hybrid surface plasmon TM mode is theoretically studied. The distribution of electromagnetic fields and the absorbance in the mode under study, the optical confinement factor, the gain, and the threshold current density in the laser under consideration are calculated. It is shown that the threshold current density at optimal layer thicknesses of an n++-Ge laser with a hybrid surface plasmon TM mode can be 2–3 times lower than the experimentally observed threshold current density in an n++-Ge laser with a conventional dielectric waveguide.
On the crystal structure and thermoelectric properties of thin Si1–xMnx films
Abstract
Thin (25 nm) Si1–xMnx/Si(100) films are fabricated by pulsed laser deposition. According to high-resolution transmission electron microscopy data, the films have a nanotextured crystalline structure and are chemically homogeneous. The temperature dependences of the resistivity and thermopower are measured in the range of 300–500 K, and the temperature dependences of the Seebeck coefficient and power factor are calculated.
Terahertz absorption and emission upon the photoionization of acceptors in uniaxially stressed silicon
Abstract
Experimental data on the spontaneous emission and absorption modulation in boron-doped silicon under CO2 laser excitation depending on the uniaxial stress applied along the [001] and [011] crystallographic directions are presented. Room-temperature radiation is used as the probe radiation. Low stress (less than 0.5 kbar) is shown to reduce losses in the terahertz region by 20%. The main contribution to absorption modulation at zero and low stress is made by A+ centers. Intersubband free hole transitions additionally contribute to terahertz absorption at higher stress. These contributions can be minimized by compensation.
Anharmonic Bloch oscillations of electrons in electrically biased superlattices
Abstract
The phenomenon of anharmonic Bloch oscillations (i.e., oscillations with a frequency which is a multiple of the Bloch frequency) is considered. The energy-band structure of silicon-carbide polytypes where these oscillations are observed is calculated ab initio. A one-dimensional model potential making it possible to calculate the Stark wave functions in a biased superlattice is constructed for these polytypes. The transfer matrix method is used to find the set of energy levels (the so-called Stark ladder) and calculate the electron wave functions. It is shown that both radiative transitions between neighboring Stark levels (at the Bloch frequency) and transitions in the form of jumps via several levels, accompanied by emission at frequencies that are multiples of the Bloch frequency, may occur. The calculated probabilities of transitions between Stark-ladder levels increase with increasing applied field strength.
Effect of thermal annealing on the photoluminescence of structures with InGaAs/GaAs quantum wells and a low-temperature GaAs layer δ-doped with Mn
Abstract
The effects of isochronal thermal annealing (at 325–725°C) on the radiative properties of InGaAs/GaAs nanoheterostructures containing a low-temperature GaAs layer δ-doped with Mn grown by laser deposition are studied. A decrease in the photoluminescence intensity and increase in the ground transition energy are observed upon thermal impact for quantum wells located near the low-temperature GaAs layer. The distribution of Mn atoms in the initial and annealed structures is obtained by secondary-ion mass spectrometry. A qualitative model of the observed effects of thermal annealing on the radiative properties of the structures is discussed; this model takes into account two main processes: diffusion of point defects (primarily gallium vacancies) from the GaAs coating layer deep into the structure and Mn diffusion in both directions by the dissociation mechanism. Magnetization studies show that, as a result of thermal annealing, an increase in the proportion of the ferromagnetic phase at room temperature (presumably, MnAs clusters) in the low-temperature GaAs coating layer takes place.
Electroluminescence from MIS silicon-based light emitters with arrays of self-assembled Ge(Si) nanoislands
Abstract
We report on the electroluminescence from silicon-based metal–insulator–semiconductor (MIS) diodes with arrays of self-assembled Ge(Si) nanoislands. Aluminum oxide (Al2O3) is used as an insulator material in the MIS contact. Variations in the electroluminescence spectra caused by changing the metal work function are examined. The intense electroluminescence from Ge(Si) nanoislands localized at a distance of 50 nm from the insulator–semiconductor interface is observed at room temperature. The emission spectrum is found to be controlled by choosing the design of the semiconductor structure and the barrier height for injected carriers.
Anisotropy of the magnetocapacitance of structures based on PbSnTe:In/BaF2 films
Abstract
The angular dependences of the capacitance of structures based on PbSnTe:In films in a magnetic field B ≤ 4 T at various bias voltages, which have a distinct anisotropic pattern in the magnetic-field direction with capacitance modulation approximately by a factor of 1.5–2, are studied experimentally at T = 4.2 K. The data obtained are compared with the experimental anisotropic angular dependences of the space-charge-limited current with current modulation up to a factor of 102–104 or greater. A qualitative model of the results obtained is considered.
Method for narrowing the directional pattern of an InGaAs/GaAs/AlGaAs multiwell heterolaser
Abstract
A semiconductor laser with a new waveguide is developed. It allows significant narrowing of the directional pattern (to 4° in the plane perpendicular to the p–n junction). In the used waveguide, the minimum excess of the effective refractive index neff of the excitation mode over the substrate refractive index ns (neff–ns ≪ 1) is provided by selecting the thickness of Al0.3Ga0.7As confinement layers, which significantly increases the waveguide mode size and leads to directional-pattern narrowing.
Edge and defect luminescence of powerful ultraviolet InGaN/GaN light-emitting diodes
Abstract
The spectrum of ultraviolet (UV) InGaN/GaN light-emitting diodes and its dependence on the current flowing through the structure are studied. The intensity of the UV contribution to the integrated diode luminescence increases steadily with increasing density of current flowing through the structure, despite a drop in the emission quantum efficiency. The electroluminescence excitation conditions that allow the fraction of UV emission to be increased to 97% are established. It is shown that the nonuniform generation of extended defects, which penetrate the active region of the light-emitting diodes as the structures degrade upon local current overheating, reduces the integrated emission intensity but does not affect the relative intensity of diode emission in the UV (370 nm) and visible (550 nm) spectral ranges.
Effect of a low-temperature-grown GaAs layer on InAs quantum-dot photoluminescence
Abstract
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.
On the condensation of exciton polaritons in microcavities induced by a magnetic field
Abstract
The photoluminescence spectra of exciton polaritons in microcavities under conditions of three-dimensional quantization are studied as a factor of the density of the optical excitation and magnetic field. The behavior of the degree of circular polarization of the exciton luminescence in a magnetic field shows that, when the concentration of excitons increases, they condense at the lowest Zeeman sublevel.
Epitaxial GaN layers formed on langasite substrates by the plasma-assisted MBE method
Abstract
In this publication, the results of development of the technology of the epitaxial growth of GaN on single-crystal langasite substrates La3Ga5SiO14 (0001) by the plasma-assisted molecular-beam epitaxy (PA MBE) method are reported. An investigation of the effect of the growth temperature at the initial stage of deposition on the crystal quality and morphology of the obtained GaN layer is performed. It is demonstrated that the optimal temperature for deposition of the initial GaN layer onto the langasite substrate is about ~520°C. A decrease in the growth temperature to this value allows the suppression of oxygen diffusion from langasite into the growing layer and a decrease in the dislocation density in the main GaN layer upon its subsequent high-temperature deposition (~700°C). Further lowering of the growth temperature of the nucleation layer leads to sharp degradation of the GaN/LGS layer crystal quality. As a result of the performed research, an epitaxial GaN/LGS layer with a dislocation density of ~1011 cm–2 and low surface roughness (<2 nm) is obtained.
Dynamic generation of spin-wave currents in hybrid structures
Abstract
Spin transport through the interface in a semiconductor/ferromagnetic insulator hybrid structure is studied by the nonequilibrium statistical operator method under conditions of the spin Seebeck effect. The effective parameter approach in which each examined subsystem (conduction electrons, magnons, phonons) is characterized by its specific effective temperature is considered. The effect of the resonant (electric dipole) excitation of the spin electronic subsystem of conduction electrons on spin-wave current excitation in a ferromagnetic insulator is considered. The macroscopic equations describing the spin-wave current caused by both resonant excitation of the spin system of conduction electrons and the presence of a nonuniform temperature field in the ferromagnetic insulator are derived taking into account both the resonance-diffusion propagation of magnons and their relaxation processes. It is shown that spin-wave current excitation is also of resonant nature under the given conditions.
Numerical simulation of the properties of solar cells based on GaPNAs/Si heterostructures and GaN nanowires
Abstract
Using methods of numerical simulation, the modes of operation are considered and structures are determined for solar cells of combined dimension based on a planar GaPNAs/Si heterostructure and an array of GaN nanowires. It is shown that the array of GaN nanowires features antireflective properties at a level no lower than 2.5% under illumination with the AM1.5D solar spectrum. The efficiency of solar cells is affected to the greatest extent by the lifetimes of minority charge carriers and the thickness of photoactive layers. It is demonstrated that the efficiency of two-junction solar cells composed of GaPNAs alloy layers and an array of GaN nanowires on a Si substrate can be as high as 32% for AM1.5D.
Simulation of electron transport in GaAs/AlAs superlattices with a small number of periods for the THz frequency range
Abstract
The electron transport in superlattices based on GaAs/AlAs heterostructures with a small number of periods (6 periods) is calculated by the Monte Carlo method. These superlattices are used in terahertz diodes for the frequency stabilization of quantum cascade lasers in the range up to 4.7 THz. The band structure of superlattices with different numbers of AlAs monolayers is considered and their current–voltage characteristics are calculated. The calculated current–voltage characteristics are compared with the experimental data. The possibility of the efficient application of these superlattices in the THz frequency range is established both theoretically and experimentally.
Magnetospectroscopy of double HgTe/CdHgTe quantum wells
Abstract
The magnetoabsorption spectra in double HgTe/CdHgTe quantum wells (QWs) with normal and inverted band structures are investigated. The Landau levels in symmetric QWs with a rectangular potential profile are calculated based on the Kane 8 × 8 model. The presence of a tunnel-transparent barrier is shown to lead to the splitting of states and “doubling” of the main magnetoabsorption lines. At a QW width close to the critical one the presence of band inversion and the emergence of a gapless band structure, similar to bilayer graphene, are shown for a structure with a single QW. The shift of magnetoabsorption lines as the carrier concentration changes due to the persistent photoconductivity effect associated with a change in the potential profile because of trap charge exchange is detected. This opens up the possibility for controlling topological phase transitions in such structures.
Study of the structures of cleaved cross sections by Raman spectroscopy
Abstract
Scanning confocal Raman spectroscopy is used to study the crystal structure of GaAs irradiated with Mn+ ions with subsequent pulse laser annealing. The scanning of cleaved cross sections of samples shows that the structure completely recovers over the depth of implantation after the annealing. Scattering in the coupled phonon–plasmon mode is revealed, which is indicative of electrical activation of the impurity at Mn doses above 1 × 1016 cm–2. The study shows the possibilities of using scanning confocal Raman spectroscopy in investigations of cleaved cross sections of structures. Using a test structure with a single δ-doped C layer, we show that the lateral resolution of the technique is 300 nm.
Wide-aperture total absorption of a terahertz wave in a nanoperiodic graphene-based plasmon structure
Abstract
The terahertz absorption spectrum in a periodic array of graphene nanoribbons located on the surface of a dielectric substrate with a high refractive index (terahertz prism) is studied theoretically. The total absorption of terahertz radiation is shown to occur in the regime of total internal reflection of the terahertz wave from the periodic array of graphene nanoribbons, at the frequencies of plasma oscillations in graphene, in a wide range of incidence angles of the external terahertz wave even at room temperature.
Investigation of the thermal stability of metastable GeSn epitaxial layers
Abstract
A stack of five elastically strained metastable GeSn layers with a thickness of 200 nm each separated by Ge spacer layers with a thickness of 20 nm is grown on a (001) Si/Ge virtual substrate. The molar fraction of Sn in the GeSn layers is 0.005, 0.034, 0.047, 0.072, and 0.10. After growth the structure is subjected to thermal annealing for 2 min at a temperature of 400°C. It is demonstrated that during the course of annealing the GeSn alloy, along with plastic relaxation, undergoes phase separation; this phase separation begins before the end of plastic relaxation. The structural degradation of the GeSn layers increases with increasing concentration of Sn accumulated on the structure surface in the form of an amorphous layer.
Nanoheterostructures with improved parameters for high-speed and efficient plasmon-polariton light emitting Schottky diodes
Abstract
As a result of theoretical and experimental analyses, the parameters of heterostructures with InAs quantum dots in a GaAs matrix are determined, which provide the development of high-speed and efficient plasmon-polariton near-infrared light-emitting Schottky diodes based on such structures. The quantum dots should be arranged on a heavily doped (to a dopant concentration of 1019 cm–3) GaAs buffer layer and be separated from the metal by a thin (10–30 nm thick) undoped GaAs cap layer. The interface between the metal (e.g., gold) and GaAs provides the efficient scattering of surface plasmon-polaritons to ordinary photons if it contains inhomogeneities shaped as metal-filled cavities with a characteristic size of ~30 nm and a surface concentration above 1010 cm–2.