I. P. Soshnikov

Atomic structure of MBE-grown GaAs nanowhiskers

The structural properties of MBE-grown GaAs and Al0.3Ga0.7 As nanowhiskers were studied. The formation of wurtzite and 4H-polytype hexagonal structures with characteristic sizes of 100 nm or larger in these materials was demonstrated. It is concluded that the Au-Ga activation alloy symmetry influences the formation of the hexagonal structure.

The Diffusion Mechanism in the Formation of GaAs and AlGaAs Nanowhiskers during the Process of Molecular-Beam Epitaxy

The formation of GaAs and AlGaAs nanowhiskers using molecular-beam epitaxy on GaAs (111)B surfaces activated with Au is theoretically and experimentally studied. It is experimentally shown that nanowhiskers whose length exceeds the effective thickness of the deposited GaAs by an order of magnitude can be grown. It is found that the experimental dependences of the nanowhisker length L on its diameter D can differ radically from those observed in the case of a vapor-liquid-solid growth mechanism. The L(D) dependences obtained in this study are decreasing functions of D. The above effects are related to the existence of the diffusion transport of atoms from the surface towards the tips of the whiskers, which leads to a considerable increase in the growth rate of thin whiskers. A theoretical model of the formation of nanowhiskers in the process of molecular-beam epitaxy is developed. The model provides a unified description of the vapor-liquid-solid and diffusion growth mechanisms and qualitatively explains the experimental results obtained.

High efficiency (ηD>80%) long wavelength (λ>1.25 μm) quantum dot diode lasers on GaAs substrates

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.

Piezoelectric effect in GaAs nanowires

The anomalous piezoelectric effect in GaAs nanowires was detected (the piezoelectric module d33 ≈ 26 pC/N). This result can be explained by the dominant content of the phase with the wurtzite-type crystal structure in GaAs nanowires and an increased pressing force on the contact layer.

Electron diffraction on GaAs nanowhiskers grown on Si(100) and Si(111) substrates by molecular-beam epitaxy

The crystal structure of GaAs nanowhiskers grown by molecular-beam epitaxy on Si(111) and Si(100) substrates is investigated using reflection high-energy electron diffraction (RHEED). It is revealed that, in both cases, the electron diffraction images contain a combination (superposition) of systems of reflections characteristic of the hexagonal (wurtzite and/or 4H polytype) and cubic (sphalerite) phases of the GaAs compound. The growth on the Si(111) substrates leads to the formation of nanowhiskers with hexagonal (wurtzite and/or 4H polytype) and cubic (sphalerite) structures with one and two orientations, respectively. In the case of the Si(100) substrates, the grown array contains GaAs nanowhiskers that have a cubic structure with five different orientations and a hexagonal structure with eight orientations in the (110) planes of the substrate. The formation of the two-phase crystal structure in nanowhiskers is explained by the wurtzite—sphalerite phase transitions and/or twinning of crystallites.

Light-emitting tunneling nanostructures based on quantum dots in a Si and GaAs matrix

InGaAs/GaAs and Ge/Si light-emitting heterostructures with active regions consisting of a system of different-size nanoobjects, i.e., quantum dot layers, quantum wells, and a tunneling barrier are studied. The exchange of carriers preceding their radiative recombination is considered in the context of the tunneling interaction of nanoobjects. For the quantum well-InGaAs quantum dot layer system, an exciton tunneling mechanism is established. In such structures with a barrier thinner than 6 nm, anomalously fast carrier (exciton) transfer from the quantum well is observed. The role of the above-barrier resonance of states, which provides “instantaneous” injection into quantum dots, is considered. In Ge/Si structures, Ge quantum dots with heights comparable to the Ge/Si interface broadening are fabricated. The strong luminescence at a wavelength of 1.55 μm in such structures is explained not only by the high island-array density. The model is based on (i) an increase in the exciton oscillator strength due to the tunnel penetration of electrons into the quantum dot core at low temperatures (T < 60 K) and (ii) a redistribution of electronic states in the Δ2-Δ4 subbands as the temperature is increased to room temperature. Light-emitting diodes are fabricated based on both types of studied structures. Configuration versions of the active region are tested. It is shown that selective pumping of the injector and the tunnel transfer of “cold” carriers (excitons) are more efficient than their direct trapping by the nanoemitter.

Gaas nanowhisker arrays grown by magnetron sputter deposition

Arrays of cone-shaped GaAs nanowhiskers (NWs) with a surface number density of up to 109 cm−2, a height ranging from 300 to 10000 nm, and a diameter of about 200 nm at the base and from 200 to 10 nm and below at the top have been obtained by means of magnetron sputtering. The characteristic NW height is proportional to the effective thickness of a deposited material layer and inversely proportional to the transverse whisker size at the top. An analysis of the NW parameters confirms the validity of the Dubrovskii-Sibirev diffusion mechanism of NW formation.

Growth of GaAs nanowhisker arrays by magnetron sputtering on Si(111) substrates

The growth of GaAs nanowhisker (NW) arrays on Si(111) substrates by magnetron sputtering is demonstrated. The characteristic NW length is proportional to the effective thickness of a deposited layer and inversely proportional to the transverse whisker size at the top. The results are explained in terms of the diffusion model of NW growth.

Formation of GaAs nanowhisker arrays by magnetron sputtering deposition

The possibility is demonstrated of fabricating arrays of cone-shaped GaAs nanowhiskers with a surface number density of up to 109 cm-2, a characteristic height ranging from 300 to 10000 nm, and a transverse size of approximately 200 nm at the base and from 200 to 10 nm or smaller at the top. The characteristic height of GaAs nanowhiskers varies in direct proportion to the effective thickness of the deposited material layer and in inverse proportion to the transverse nanowhisker size at the top. The growth of GaAs nanowhiskers is studied as a function of the deposition rate, the temperature, and the crystallographic orientation of the substrate. From an analysis of the obtained dependences of the nanowhisker size on these parameters, it is concluded that GaAs nanowhiskers are formed through the diffusion mechanism.

Composition analysis of coherent nanoinsertions of solid solutions on the basis of high-resolution electron micrographs

A program package is presented, ensuring fast direct and inverse Fourier transformations of images, various methods of noise filtration and use of spectral windows, and determination of local interplanar spacings (LIS) from cross-sectional high-resolution electron micrographs. The algorithm for determining the LIS consists in obtaining, by double fast Fourier transformation, a high-resolution image filtered by selecting an appropriate combination of reflections and using this image to find the characteristic LIS. A specific feature of this algorithm is that it employs weighting with correction of the integration domain. The resulting maps of LIS can be used to determine the chemical composition, e.g., in substitutional solid solutions, such as AxB1−x, AxB1−xC. The method is applied to process a high-resolution electron micrograph of a heterostructure with a submonolayer InGaAs/GaAs lattice.