M. L. Zanaveskin

Characterization of single-crystal sapphire substrates by X-ray methods and atomic force microscopy

The possibility of characterizing a number of practically important parameters of sapphire substrates by X-ray methods is substantiated. These parameters include wafer bending, traces of an incompletely removed damaged layer that formed as a result of mechanical treatment (scratches and marks), surface roughness, damaged layer thickness, and the specific features of the substrate real structure. The features of the real structure of single-crystal sapphire substrates were investigated by nondestructive methods of double-crystal X-ray diffraction and plane-wave X-ray topography. The surface relief of the substrates was investigated by atomic force microscopy and X-ray scattering. The use of supplementing analytical methods yields the most complete information about the structural inhomogeneities and state of crystal surface, which is extremely important for optimizing the technology of substrate preparation for epitaxy.

The effect of the memristor electrode material on its resistance to degradation under conditions of cyclic switching

The stability of titanium oxide memristors with gold and platinum electrodes with respect to switching-induced degradation has been studied. It is established that the use of gold instead of platinum as the electrode material significantly increases the resistance of a memristor to degradation in the course of repeated resistance read-write(erase) cycles. The first Russian high-endurance memristor based on titanium oxide has been obtained, which can withstand up to 3000 resistive switching cycles.

Growth of AlGaN under the conditions of significant gallium evaporation: Phase separation and enhanced lateral growth

The growth kinetics of AlGaN in NH3 MBE under significant Ga desorption was studied. It was found that the addition of gallium stimulates 2D growth and provides better morphology of films compared to pure AlN. The effect was experimentally observed at up to 98% desorption of the impinging gallium. We found that under the conditions of significant thermal desorption, larger amounts of gallium were retained at lateral boundaries of 3D surface features than at flat terraces because of the higher binding energy of Ga atoms at specific surface defects. The selective accumulation of gallium resulted in an increase in the lateral growth component through the formation of the Ga-enriched AlGaN phase at boundaries of 3D surface features. We studied the temperature dependence of AlGaN growth rate and developed a kinetic model analytically describing this dependence. As the model was in good agreement with the experimental data, we used it to estimate the increase in the binding energy of Ga atoms at surface defects...

Effect of reactive ion etching on the surface of polymethylmethacrylate

The influence of oxygen-, fluorine-, and argon-containing plasmas on the morphology of the surface of polymethylmethacrylate during reactive ion etching is investigated. A series of experiments on polymer surface etching microns is performed at different gas compositions (O2, N2, Ar, O2/N2, O2/Ar, CF4, and O2/CF4). It is demonstrated that the etching depth and surface roughness of the material increase with increasing RF oscillator power and, moreover, depend considerably on the composition and percentage ratio of gases injected into the chamber.

A study of the effect of the oxygen index of the target on the critical characteristics of YBa2Cu3Ox epitaxial layers formed by pulsed laser deposition

The effect of radiative heating of the surface of an HTS target on its oxygen index during the growth of HTS coatings by pulsed laser deposition is studied. It is shown that, during growth, the oxygen index of the HTS target varies in a range of 6.85–6.12. It is revealed that the oxygen index of HTS coatings formed by pulsed laser deposition does not depend on the oxygen index of the sputtering target at an identical cationic composition.

Formation of ultrasmooth thin silver films by pulsed laser deposition

Ultrasmooth thin silver films have been formed on a quartz substrate with a buffer yttrium oxide layer by pulsed laser deposition. The dependence of the surface morphology of the film on the gas (N2) pressure in the working chamber and laser pulse energy is investigated. It is found that the conditions of film growth are optimal at a gas pressure of 10−2 Torr and lowest pulse energy. The silver films formed under these conditions on a quartz substrate with an initial surface roughness of 0.3 nm had a surface roughness of 0.36 nm. These films can be used as a basis for various optoelectronics and nanoplasmonics elements.

The surface roughness investigation by the atomic force microscopy, x-ray scattering, and light scattering

Roughness investigation of the polished quartz and sital substrates, used as substrates for multilayer interference mirrors in circle laser gyroscopes, were carried out. Atomic force microscopy, x-ray scattering and angle-resolved scattering instruments were used. The power spectral density function and effective rms roughness were calculated. Good correlation of power spectral density functions and effective rms roughness was shown for all instruments. Essentially difference of the polishing quality was shown for sital substrates manufactured by two different producers.

Tunneling Current in Oppositely Connected Schottky Diodes Formed by Contacts between Degenerate n-GaN and a Metal

The nonlinear behavior of the I–V characteristics of symmetric contacts between a metal and degenerate n-GaN, which form oppositely connected Schottky diodes, is investigated at free-carrier densities from 1.5 × 1019 to 2.0 × 1020 cm–3 in GaN. It is demonstrated that, at an electron density of 2.0 × 1020 cm–3, the conductivity between metal (chromium) and GaN is implemented via electron tunneling and the resistivity of the Cr–GaN contact is 0.05 Ω mm. A method for determining the parameters of potential barriers from the I–V characteristics of symmetric opposite contacts is developed. The effect of pronounced nonuniformity of the current density and voltage distributions over the contact area at low contact resistivity is taken into account. The potential-barrier height for Cr–n+-GaN contacts is found to be 0.47 ± 0.04 eV.

Influence of High-Temperature Annealing of the Textured Metal Ni–W Substrate on the Structural Properties of Seed Layer in HTS 2G tapes

The surface reconstruction of the textured metal tapes at the temperatures typical for the formation of the seed buffer Y2O3 layer of HTS 2G tapes have been revealed and studied for the first time. The influence of a terrace structure of the substrate surface on the characteristics of the texture of the seed Y2O3 layer has been shown. This effect is critically important to the deposition of buffer layers on the moving tape and allows to expand the temperature range of growth, in which the full inheritance of substrate texture by the seed Y2O3 layer is occurred.

On the Growth of High-Temperature Epitaxial AlN (AlGaN) Layers on Sapphire Substrates by Ammonia Molecular Beam Epitaxy

The growth of high-temperature AlN and AlGaN layers on (0001) sapphire substrates by ammonia based molecular-beam epitaxy is studied. Factors affecting the formation of inverted domains in high-temperature AlN films are examined. The density of inverted domains is found to correlate with the density of nucleation islands during the initial stages of growth. The denser coverage of a surface by nucleation islands suppresses the formation of inverted domains. It is possible to increase the density of surface coating at the nucleation growth stage by increasing the degree of substrate nitriding, reducing the deposition temperature, and using intense ammonia fluxes during deposition of the initial layers. The kinetic model in the mean field approximation is developed to explain the observed effects of growth parameters on the density of nucleation islands. The growth features of AlN and its structure are taken into account. The obtained results are used to grow AlN/AlGaN layers with improved structural quality. The grown films have a root-mean-square surface roughness of 2 Å and 120 arc s FWHM of X-ray diffraction peaks for the AlN 0002 reflection. The density of inverted domains is decreased to below 105 cm-2. Improvement in the quality of the AlN films is achieved by using two-step growth and by the application of gallium as a surfactant.