N. K. Polyakov

Formation of InAs quantum dots on a silicon (100) surface

At moderate arsenic fluxes and substrate temperatures (470 ) InAs grows on Si (100) surface in the Stranski-Krastanow growth mode with the formation of mesoscopic dislocated clusters on top of a two-dimensional periodically corrugated InAs wetting layer. In contrast, at lower temperatures (250 ) a dense array of self-organized nanoscale InAs quantum dots of uniform size and shape is formed. These quantum dots, when grown on a Si buffer layer and covered with a Si cap, give a luminescence line at about 1.3 m.

Structure and optical properties of Si'InAs'Si layers grown by molecular beam epitaxy on Si substrate

Epitaxial Si/InAs/Si heterostructure grown on (001) Si substrate by molecular beam epitaxy and annealed at 800 °C was investigated by high resolution transmission electron microscopy. Extensive interdiffusion leads to the formation of an InAs solid solution in the Si cap layer. Additionally, InAs-enriched regions with extensions of ∼6 nm, which exhibit two kinds of ordering are observed. The ordering of InAs molecules has occurred, respectively, in (101) and (101) planes inclined and (110) and (110) planes parallel to the [001] growth direction. It is attributed to the energy gain from the reduced number of mixed Si–As and Si–In bonds. The sample show photoluminescence in the 1.3 μm region, which is tentatively attributed to the recombination of excitons localized in the ordered regions.

STM and RHEED study of InAsGaAs quantum dots obtained by submonolayer epitaxial techniques

Formation of uniform arrays of InAs quantum dots on GaAs(100) singular and vicinal (3° towards [011] direction) surfaces crucially depends on the deposition mode chosen. For dots formed with continuous As flux impinging on the surface and simultaneous submonolayer In deposition cycles, intentional substrate misorientation significantly decreases the density of dots and stimulates their ordering along the [001] direction. On the contrary, growth using alternate In and As deposition cycles results in a reduced density of dots for singular surfaces and in strongly increased dot concentration for vicinal ones. Ordering of dots in chains along [001] and [010] directions is observed for the alternative deposition on singular substrates.

Study of processes of self-catalyzed growth of gaas crystal nanowires by molecular-beam epitaxy on modified Si (111) surfaces

The processes of growth of self-catalyzed GaAs crystal nanowires on Si (111) surfaces modified by three different methods are studied. For the technology of production of the GaAs nanowires, molecular-beam epitaxy is used. It is found that, in the range of substrate temperatures between 610 and 630°C, the surface density of nanowires and their diameter sharply increases, whereas the temperature dependence of the nanowire length exhibits a maximum at 610°C. An increase in the temperature to 640°C suppresses the formation of nanowires. The method that provides a means for the fabrication of purely cubic GaAs nanowires is described. A theoretical justification of the formation of the cubic phase in self-catalyzed GaAs nanowires is presented.

The emission from the structures with arrays of coupled quantum dots grown by the submonolayer epitaxy in the spectral range of 1.3–1.4 µm

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.

Formation of InGaAsGaAs quantum dots by submonolayer molecular beam epitaxy

Abstract We have performed a scanning tunneling microscopy study of the formation of (In,Ga)As/GaAs and InAs/GaAs quantum dot and quantum wire arrays on GaAs(100) and vicinal surfaces during submonolayer molecular beam epitaxy. During the initial stage of strained layer transformation (∼ 2 monolayers of InAs) the formation of well ordered quantum wire arrays along the [001] direction is observed. Further deposition results in dots placed in rows and then in an array of well separated dots. This effect is more pronounced in the case of vicinal surfaces where the dots are oriented along the [001] direction despite the surface is misoriented towards the [0 – 11] direction. Our study provides a new insight into the process of quantum dot and quantum wire arrays formation on GaAs(100) and vicinal surfaces.

Structural and optical properties of InAs quantum dots in AlGaAs matrix

Structural and optical properties of InAs quantum dots (QDs) grown in a wide-bandgap Al0.3Ga0.7As 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 ∼1.18 µm with the effective thickness of InAs in Al0.3Ga0.7As 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 ~1.3 µm is demonstrated.

Heteroepitaxial growth of InAs on Si: A new type of quantum dot

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 77K and 1.6 µm at 300 K.

Super-radiant mode in InAs—monolayer–based Bragg structures

We report direct experimental evidence of the collective super-radiant mode in Bragg structure containing 60 InAs monolayer-based quantum wells (QWs) periodically arranged in GaAs matrix. Time-resolved photoluminescence measurements reveal an appearance of the additional super-radiant mode, originated from coherent collective interaction of QWs. This mode demonstrates a super-linear dependence of the intensity and radiative decay rate on the excitation power. The super-radiant mode is not manifested in the case if only a small number of QWs is excited.

Properties of InGaAsN heterostructures emitting at 1.3–1.55 µm

A comparative study of two types of heterostructures with quantum-size InGaAsN/GaAs layers in a GaAs matrix formed by molecular beam epitaxy is performed. The first type of heterostructure consists of InGaAsN layers deposited in a conventional continuous mode. The active part of the second type of heterostructure (HS) is formed by submonolayer InAs insertion confined by InGaAsN HS layers, surrounded by short period GaAsN/InGaAsN superlattices. The structures under investigation emit in a wavelength range 1.3–1.55 µm at room temperature. It is shown that lower averaged nitrogen and indium concentrations are needed to realize the emission at 1.5 µm in the case of the second type of HS.