P. A. Yunin

Monolithically integrated InGaAs/GaAs/AlGaAs quantum well laser grown by MOCVD on exact Ge/Si(001) substrate

We report on realization of the InGaAs/GaAs/AlGaAs quantum well laser grown by metallorganic chemical vapor deposition on a virtual Ge-on-Si(001) substrate. The Ge buffer layer has been grown on a nominal Si(001) substrate by solid-source molecular beam epitaxy. Such Ge buffer possessed rather good crystalline quality and smooth surface and so provided the subsequent growth of the high-quality A3B5 laser structure. The laser operation has been demonstrated under electrical pumping at 77 K in the continuous wave mode and at room temperature in the pulsed mode. The emission wavelengths of 941 nm and 992 nm have been obtained at 77 K and 300 K, respectively. The corresponding threshold current densities were estimated as 463 A/cm2 at 77 K and 5.5 kA/cm2 at 300 K.

Impact of growth and annealing conditions on the parameters of Ge/Si(001) relaxed layers grown by molecular beam epitaxy

Influence of the Ge layer thickness and annealing conditions on the parameters of relaxed Ge/Si(001) layers grown by molecular beam epitaxy via two-stage growth is investigated. The dependences of the threading dislocation density and surface roughness on the Ge layer thickness, annealing temperature and time, and the presence of a hydrogen atmosphere are obtained. As a result of optimization of the growth and annealing conditions, relaxed Ge/Si(001) layers which are thinner than 1 μm with a low threading dislocation density on the order of 107 cm–2 and a root mean square roughness of less than 1 nm are obtained.

Depth profiling of fullerene-containing structures by time-of-flight secondary ion mass spectrometry

A new variant of depth profiling for thin-film fullerene-containing organic structures by the method of time-of-flight (TOF) secondary ion mass spectrometry (SIMS) on a TOF.SIMS-5 setup is described. The dependence of the yield of C60 molecular ions on the energy of sputtering ions has been revealed and studied. At an energy of sputtering Cs+ ions below 1 keV, the intensity of C60 molecular ions is sufficiently high to make possible both elemental and molecular depth profiling of multicomponent (multilayer) thin-film structures. Promising applications of TOF-SIMS depth profiling for obtaining more detailed information on the real molecular composition of functional organic materials are shown.

Peculiarities in magnetron sputtering of YBCO epitaxial films for applications in superconductor electronics devices

We consider the main factors determining the growth of YBa2Cu3O7–δ high-Tc superconductor films during magnetron sputtering in the planar axial geometry. Special attention is paid to the increase of the growth rate of the films suitable for superconductor electronics devices. Magnetron sputtering is used for obtaining YBa2Cu3O7–δ films with high structural and electrophysical characteristics for a growth rate up to 200 nm/h, which were used in constructing microwave disk resonators and long Josephson junctions on bicrystal substrates. The unloaded Q factor of cavities exceeds 80000 at a frequency of 7.1 GHz at a temperature of 77 K, which corresponds to the best results in this field. Josephson junction of length 50–350 μm are characterized by critical current density jc = 12–33 kA/cm2 at T = 77 K and jc = 93–230 kA/cm2 at T = 6 K in zero magnetic field. The characteristic voltage IcRn is 0.8–1.96 mV.

Quantitative calibration and germanium SIMS depth profiling in GexSi1 − x/Si heterostructures

Methods for minimizing nonlinear matrix effects in the quantitative determination of germanium concentrations in GexSi1 − x layers by secondary ion mass spectrometry are discussed. The analysis conditions with positive SiCs+, GeCs+ and negative Ge−, Si− secondary ions produced during sputtering by cesium ions are used in the TOF.SIMS-5 setup with a time-of-flight mass analyzer. In contrast to published works for TOF.SIMS setups, the linear dependence of the ion-concentration ratio Ge−/Si− on x/(1 − x) is shown. Two new linear calibrations for the germanium concentration as a function of the cluster Ge2− secondary ion yield are proposed. The calibration factors are determined for all linear calibrations at various energies of sputtered cesium ions and Bi+ and probe Bi3+ ions. It is shown for the first time that the best depth resolution among the possible conditions of quantitative germanium depth profiling in GexSi1 − x/Si multilayer heterostructures is provided by the calibration mode using elemental Ge− and Si− negative secondary ions.

Method for taking into account the shift parameter in the deconvolution of the depth composition distribution of semiconductor structures from SIMS depth profiles

A method for solving the direct and inverse problems of depth profiling in secondary-ion mass spectrometry is suggested. The advantages of solving the incorrect inverse problem in Fourier space with regularization by the Tikhonov method are discussed. Upon the reconstruction of element-concentration profiles, special attention is given to their shift as a feature of the SIMS resolution function. Consideration of the shift is achieved by joint solution of the direct and inverse problems of depth profiling. Examples of the operation of the deconvolution algorithm for both simulated and experimental profiles are given. It is shown that use of the proposed deconvolution algorithm makes it possible to increase the informativity and improve the depth resolution of the method. The suggested method for taking into account the shift enables us to avoid regular error in determining the position of thin layers near the surface.

GaAs/Ge/Si epitaxial substrates: Development and characteristics

We developed high quality 2-inch GaAs/Ge/Si (100) epitaxial substrates, which may be used instead of GaAs monolithic substrates for fabrication of solar cells, photodetectors, LEDs, lasers, etc. A 200–300 nm Ge buffer layer was grown on Si substrates using the HW-CVD technique at 300°C, a tantalum strip heated to 1400°C was used as the “hotwire”. The MOCVD method was used to grow a 1 μ GaAs layer on a Ge buffer. The TDD in the GaAs layers did not exceed (1–2)∙105 cm-2 and the surface RMS roughness value was under 1 nm.

New hybrid material based on multiwalled carbon nanotubes decorated with rhenium nanoparticles

The deposition of rhenium nanoparticles on the surface of multiwalled carbon nanotubes (MWCNTs) is conducted by metal organic chemical vapor deposition (MOCVD) technology. The synthesized hybrid materials are analyzed using scanning electron microscopy, high-resolution transmission electron microscopy and powder X-ray diffraction. The dependence of the sizes and shapes of the deposited rhenium nanoparticles on the initial synthesis parameters is established. It is found that the size distribution of rhenium nanoparticles is bimodal on the surface of MWCNTs.

Features of InN growth by nitrogen-plasma-assisted MBE at different ratios of fluxes of group-III and -V elements

The results of investigations of the effect of the ratios of fluxes of the Group-III and -V elements on the structural and optical properties of an InN film deposited by plasma-assisted molecular-beam epitaxy (MBE) are presented. It is shown that the InN layer consists of free-standing nanocolumns at a flux ratio of III/V < 0.6. InN growth becomes two-dimensional (2D) in the ratio range 0.6 < III/V < 0.9; however, the InN layer has a nanoporous structure. Upon passage to metal-rich conditions of growth (III/V ∼1.1), the InN layer becomes continuous. The passage from 3D to 2D growth is accompanied by an increase in the threading-dislocation density. It results in a decrease in the photoluminescence (PL) intensity of InN at room temperature. The electron concentration in the InN layers amounts to ∼5 × 1018 cm–3, which results in a shift of the PL-signal peak to the wavelength region of 1.73–1.8 μm and to a shift of the absorption edge to the region of ∼1.65 μm.

On the use of an external reference sample in the X-ray diffraction analysis of epitaxial layers

The differences in the high-resolution X-ray patterns for measurement of the crystal-lattice constant with and without the use of an external reference sample are discussed. The calculation procedures in the measurement of the lattice constant are compared. The results of the measurements of a Si(111) test crystal using a Bruker D8 Discover diffractometer are presented, and the examples of the use of this crystal as an external reference are described.