Table of contents

Editorial Preface

The 18^th Russian Young Conference on Physics of Semiconductors and Nanostructures, Opto- and Nanoelectronics was held on November 28 – December 2, 2016 at Peter the Great St. Petersburg Polytechnic University.

The program of the Conference included semiconductor technology, heterostructures with quantum wells and quantum dots, opto- and nanoelectronic devices and new materials. A large number of participants with more than 200 attendees from many regions of Russia provided a perfect platform for the valuable discussions between students and experienced scientists.

Conference included two invited talks given by Doctor of Science I.S. Burmistrov ("Topology in condensed matter physics") and Dr. N.V. Kryzhanovskaya ("Micro-lasers with whispering-gallery modes"). Students, graduate and postgraduate students presented their results on plenary and poster sessions. The total number of accepted papers published in Russian (the official conference language) was 138. Here we publish 42 of them in English.

Like previous years, the participants were involved in the competition for the best report. Certificates and cash prizes were awarded to a number of participants for the presentations selected by the Program Committee. Two special E.F. Gross Prize were given for the best presentation in semiconductor optics. Works with potential applications were recommended for participation in the following competition for support from the Russian Foundation for Assistance to Small Innovative Enterprises in Science and Technology.

The conference was supported by the Russian Foundation for Basic Research and the innovation company "ATC – Semiconductor Devices", St. Petersburg.

Editors

R.A. Suris

L.E. Vorobjev

D.A. Firsov

V.A. Shalygin

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Spin transport of conduction electrons in silicon samples doped with bismuth in the 1.1·10¹³ - 7.7·10¹⁵ cm^-3 concentration range was studied by the Hall effect measurements. The dependence of the Hall voltage magnitude on the magnetic field is the sum of the normal and spin Hall effects. The electrons are partially polarized by an external magnetic field and are scattered by the bismuth spin-orbit potential. Spin-flip scattering results in the additional electromotive force which compensates the normal Hall effect in strong magnetic fields.

We report photoluminescence investigations of heavily doped Al_xGa_1-xN:Si films grown by molecular beam epitaxy on sapphire substrates. The wide intensive defect-related band dominates in the photoluminescence spectra of Al_xGa_1-xN:Si films with the Al content higher than 0.46 covering the whole visible spectral range. This band is attributed to donor-acceptor transitions. The acceptor ionization energy of about 1.87 eV for heavily doped AlN:Si was obtained, decrease of Al content leads to decrease of the acceptor ionization energy. The donor was assigned to the Si atom on the Ga/Al site; the acceptor might be the (2-/3-) transition level of the V_Al.

Magnetoreflection of unpolarized infrared radiation for single crystals of magnetostrictive cobalt ferrite spinel was studied. The correlation between magnetoreflection and magnetoelastic properties of that type of spinel was observed. It is shown that the magnetoreflection is the most pronounced in the region of a middle-infrared impurity band and reflection minima near phonon bands.

We studied theoretically and experimentally plasmon-phonon polaritons and longitudinal plasmon-phonon oscillations in n-GaN epitaxial layers. The studies were carried out on the epitaxial layers with various doping levels. Simulation of the reflectivity spectra and dispersion relations of plasmon-phonon polaritons was performed in a wide frequency range. Reflectivity spectra transformation associated with phonon damping and electron relaxation processes has been revealed. Experimental studies of the reflectivity spectra have been performed in the spectral range of 8–80 meV. The experimental spectra are well fitted by the simulated ones. Results of the study can be used for contactless determination of the electron concentration and mobility in GaN epitaxal layers.

Time dependences of the magnetic moment m(t) in GaMnSb thin films with MnSb clusters are measured. The m(t) dependences are straightened in semi-logarithmic coordinates m(lnt). The field dependences of magnetic viscosity S(H) corresponding to the slope of straight lines m(lnt) are studied. It is demonstrated that the behaviour of dependences S(H) is governed by the magnetic moment fluctuations of MnSb clusters with lognormal distribution of the magnetic anisotropy energy.

The temperature dependences of electrical conductivity, thermoelectric power and thermoelectric power factor of solid solutions of the PbTe system doped with up to 3 mol% CdSe have been studied in the present work. The dependences show that these parameters reach their maximum values at a CdSe concentration of 3 % in the temperature range of 420-450 K with α = 310 µV/K, σ = 210 (Ohm·cm)^–1 and P = 15.1 µW/(cm·K²).

We have studied the composite nanoperiodic (3-8 nm) SiO_x/Al₂O₃ structures fabricated by physical deposition from separate sources. The structures annealed in nitrogen atmosphere at 900–1100 °C included Si-NCs that showed intense room-temperature photoluminescence at 1.6 eV. The quantum-confinement peak shift was observed under varying the SiO_x layer thickness. Up to fourfold intensity enhancement was observed after hydrogenation of the structures in the range of 400–450 °C for 2 hours.

GaAs thermal smoothing at temperatures T ≤ 650°C in the conditions close to equilibrium yields surfaces with atomically smooth terraces separated by steps of monatomic height. At higher temperatures T ≥ 700°C, surface smoothing is changed to roughening. In the present paper, possible reasons of surface roughening at elevated temperatures are studied by means of Monte Carlo simulation and compared with the experimental results on GaAs. It is proved that the thermodynamic roughening transition, which consists in spontaneous generation of atomic steps due to decrease in the step line tension down to zero, cannot explain the experiment because it should occur at temperatures T ∼ 1800 - 2000°C, i.e. much higher than in the experiment. Kinetic instabilities caused by deviations from equilibrium towards growth or sublimation are shown to cause GaAs roughening at elevated temperatures. The microscopic mechanisms of kinetic-driven roughening are discussed.

Authors represent utilizing UHV Ga FIB for preparing a Si₃N₄/GaN substrate for submicron selective-area epitaxy. In result, GaN submicron stripes were grown in the 100, 200 and 500 nm windows of a Si₃N₄ mask layer. SEM investigations show good crystalline perfection of the grown stripes.

We report on the experimental observation of photoconductivity (PC) in ultrathin (≈ 40 nm thick) ZrO₂(Y) films with single layered arrays of Au nanoparticles (NPs) of 1 to 3 nm in diameter. The samples were prepared by the deposition of islanded Au films of ∼1 nm in thickness sandwiched between two ZrO₂(Y) layers by Magnetron Sputtering followed by annealing. The effect of PC was attributed to the photoexcitation of the collective plasmon oscillations in dense Au NP arrays. The temperature dependencies and kinetics of PC have been studied. At 300 K, the PC has been found to originate mainly from heating of ZrO₂(Y) due to plasmon optical absorption in Au NPs (the bolometric effect). At 77 K, the photoresponse has been attributed to plasmon-assisted electron transport between NPs via the vacancy α-band in ZrO₂(Y) barriers.

We have observed a phenomenon of formation of a thin bilayer Pt₃Si/Pt₂Si film at room temperature on poly-Si substrates in the process of Pt magnetron sputtering and wet etching, obtained such a film and investigated its structure and phase composition. By direct X-ray photoelectron-spectroscopic measurements, we have verified our previous observation of the Pt₂Si layer formation between Pt and poly-Si films as a result of Pt magnetron sputtering at room temperature. This layer likely appears due to a high enough temperature of Pt ions in the magnetron plasma, sufficient for the chemical reaction of the silicide film formation on the Si surface. The Pt₃Si layer likely forms from the Pt–Pt₃Si layer (Pt₉₅Si₅), which arises under a Pt film during magnetron sputtering, as a result of Pt removal by wet etching.

Graphene samples synthesized by chemical vapor deposition, transferred onto Si/SiO₂ substrates by the standard technology using PMMA, and then annealed in a reductive atmosphere have been characterized by XPS observations and measurements of the resistance temperature dependence. It was shown, that most of as-transferred samples exhibit a metallic-like resistivity dependence but some of them can demonstrate a non-metallic one. A comparative analysis of the results obtained by the XPS study and resistance measurements allowed us to conclude that the conduction process in CVD graphene is directly affected by functional groups adsorbed on the sample surface. Annealing in a mixture of H₂ and Ar at T = 250–750°C is shown to result in a cleaning of the graphene surface from adsorbed contaminations and in a modification of the resistance temperature dependence which demonstrates a higher slope in case of a metallic-like behavior for as-transferred samples and a suppression of the activation-type dependence in case of a non-metallic one.

The electrical conductivity studies of the Cu/ZnO/Si thin film heterostructures were carried out by the current-voltage (I-V) characteristics. It was found that the I-V characteristics were asymmetric and showed weak rectifying properties. The most probable mechanism of electrical conductivity was determined. The concentration of trapping levels and the carrier mobility were calculated.

This article describes the reduction process of graphene oxide films deposited on various substrates by 445 nm laser irradiation with exposure time from 4·10^-3 to 3·10^-1 s. AFM images of the deposited films are presented. To obtain a better quality of the reduced graphene oxide films on substrates, we found the optimal ratio of the partial pressures of air and argon in the background environment. Variation of laser irradiation exposure time allowed us to determine its influence on sheet resistance and the ratio of Raman peaks intensities I_D/I_G, I_2D/I_G of the reduced material. As a result, we demonstrated the possibility of graphene conductive traces formation with a sheet resistance of 188 Ohm/□ at 0.1 um film thickness.

In the paper we investigate the Ge island nucleation on a Si(100) surface which was annealed to obtain the diatomic steps. It was observed that the islands tend to nucleate at the step edges.

The transition from a dipolar to a spatially direct electron-hole liquid in two-dimensional layers of a type-II (buffer Si_1-yGe_y)/tSi/sSi_1-xGe_x/tSi/(cap Si_1-yGe_y) heterostructure is investigated by photoluminescence spectroscopy at liquid-helium temperatures at high excitation levels. The transition takes place upon a reduction of the thickness of the sSi_1-xGe_x layer, which forms a quantum well for holes in the valence band and a barrier in the conduction band separating the electron quantum wells (tSi layers). The main characteristics of both types of electron-hole liquid are determined. The lifetime of dipolar excitons is determined from photoluminescence kinetics measurements.

The photoluminescence in nanostructures with InGaAsSb/AlGaAsSb quantum wells of different widths is investigated experimentally under different pumping levels and theoretically. The experimentally determined dependencies of photoluminescence intensity on the optical pumping level are compared with the calculated dependences of photoluminescence intensity on the nonequilibrium carrier concentration. The presence of resonant nonradiative Auger recombination in one of the investigated samples is proved by the comparison between experiment and calculations.

The effects of discontinuities of the material parameters at the interfaces of narrow GaAs-based quantum wells as well as of the nonparabolicity of the conduction band on the exciton binding energy are studied. These effects are taken into account in the three-dimensional Schrödinger equation for the exciton. Accurate exciton ground state energies are obtained using the improved numerical scheme of Khramtsov et al. (2016 J. Appl. Phys. 119 184301). The enhancement of the exciton binding energy for narrow quantum wells is observed and the contribution of each effect is estimated.

Optical transmission and reflection for a single GaN/AlGaN heterojunction grown on sapphire have been investigated with high and low spectral resolution in the spectral range of 8–47 meV. For comparison, the same spectra have been measured for the sapphire substrate. Refractive index dispersion has been determined for sapphire from the spectra measured with high resolution. Then the data on 2D electron absorption in the GaN/AlGaN heterojunction were obtained from the low resolution spectra. The spectra of terahertz emission from the GaN/AlGaN heterojunction under 2D electron heating in strong electric field have been measured for the first time.

Temperature and composition dependencies of the critical thickness of transition from two-dimensional to three-dimensional growth for GeSiSn films on Si(100) with a lattice mismatch of 1 – 5% were experimentally determined. To understand the Sn influence on growth of SiGeSn/Si multi-quantum wells, the phase diagram of surface superstructures during the growth of pure Sn on Si(100) was created. A possibility of synthesizing multilayer structures by molecular beam epitaxy was shown, and the crystal lattice constants were determined using high-resolution transmission electron microscopy. We obtained GeSiSn/Si MQW structures which demonstrated photoluminescence for the Sn content in GeSiSn layers of up to 6%.

Elastically strained metastable GeSn layers with mole fraction of tin up to 0.15 was grown on (001) Si substrates with different misorientation. Photoluminescence spectra (PL) at room temperature and infrared (IR) spectroscopy spectra at helium temperature were measured. The direct edge of intrinsic absorption in the region of 0.71-0.72 eV was observed in grown structures with a tin content of about 12-13%.

The paper presents the results of electrochemical capacitance-voltage profiling and simulation of quantum-sized semiconductor structures with quantum wells and delta-doped layers based on gallium arsenide. The experimental ECV data were obtained by superposition of measured capacitance-voltage characteristics during the gradual etching of the nanostructure. As a result of simulation, the concentration distribution and energy lineups for structures with delta-layers and quantum wells in gallium arsenide were calculated. The results of simulation are in qualitative agreement with the experimental results and data found in literature.

We present a theoretical investigation of persistent spin helices in two-dimensional electron systems with spin-orbit coupling. For this purpose, we consider a single-particle effective mass Hamiltonian with a generalized linear-in-k spin-orbit coupling term corresponding to a quantum well grown in an arbitrary crystallographic direction, and derive the general condition for the formation of the persistent spin helix. This condition applied for the Hamiltonians describing quantum wells with different growth directions indicates the possibility of existence of the persistent spin helix in a wide class of 2D systems apart from the [001] model with equal Rashba and Dresselhaus spin-orbit coupling strengths and the [110] Dresselhaus model.

We have studied MOCVD-grown structures with InAs layers in GaAs and metamorphic InGaAs matrices. Deposition of 2 ML of InAs in a GaAs or In_0.24Ga_0.76As matrix results in quantum dots formation with photoluminescence (PL) peaks at 1240 and 1380 nm, respectively. In case of deposition of 2 ML of InAs in a In_0.30Ga_0.70As metamorphic matrix, formation of a corrugated quantum well emitting at 1450 nm has been revealed. The integrated PL intensity of the metamorphic structures is much higher than that for the GaAs based structure. For the metamorphic structures, the thermal escape of carriers from InAs quantum dots (a quantum well) results in high intensity of the PL line due to InGaAs matrix at room temperature.

We report on single photon emission from single CdTe/ZnTe quantum dots (QDs) grown by thermally-activated molecular beam epitaxy providing a reduced QD lateral density below 10¹⁰ cm^-2. For micro-photoluminescence spectroscopy studies and correlation measurements, the mesa structures of 200 and 500 nm diameters are fabricated by combination of electron-beam lithography and reactive plasma etching. Autocorrelation function of photons emitted from a single QD under cw excitation demonstrates antibunching with a value of g⁽²⁾(0) ∼ 0.3 that is a signature of non-classical light.

Photoinduced and equilibrium optical transmission was studied in undoped and δ-doped Ge/Si quantum dot structures in the far-infrared spectral range. Multi-particle excitations were observed in the absorption spectra of the structures with different doping levels. Photoinduced absorption spectra demonstrate the thermal distribution of the photoexcited holes over the single-particle states of the quantum dot ensemble in contrast with the equilibrium absorption spectra.

In this work a series of relaxation curves of photoinduced intraband absorption and interband photoconductivity were measured in Ge/Si quantum dots in the temperature range from 80 K to 300 K and at different levels of the interband excitation. The low-temperature experimental curves show a two-step decay of a population of quantum dots. At high temperatures there is only one decay component. A simultaneous analysis of photoinduced intraband absorption and interband photoconductivity relaxation curves shows that quantum dots act as traps for non-equilibrium holes only at low temperatures.

In this work we have applied the low-energy high-density low-pressure radio-frequency inductively coupled argon plasma treatment to the Cu(In,Ga)(S,Se)₂ thin films grown on glass substrates using a selenization/sulfurization process. This approach allowed to obtain nanowires with an average height varying from 120 to 240 nm and with a 15-50 nm diameter. It is shown that the mechanism of the nanowire formation is plasma-assisted vapor-liquid-solid growth in combination with micromasking with In-Ga alloy nanoinclusions serving both as catalyst droplets and micromasks.

We present an analytical solution to the boundary-value problem in the classical theory of elasticity for a core-shell nanowire with an eccentric parallelepipedal core of an arbitrary rectangular cross section. The core is subjected to one-dimensional cross dilatation eigenstrain. The misfit stresses are found in a concise and transparent closed form which is convenient for practical use in theoretical modeling of misfit relaxation processes.

The relation between the magnetic viscosity of exotic ε-In_0.24Fe_1.76O₃ nanoparticles and 1/f magnetic noise caused by the random thermally activated magnetization reversal of a single nanoparticle was found.

Within the frames of the research described in the paper, 1D ZnO nanostructures on flexible substrates were synthesized by the hydrothermal method. The paper describes technological features of obtaining oxide nanorods using low-temperature synthesis. Morphological properties of obtained structures were investigated.

The features of the surface topography and the local energy spectrum of the graphene layer placed on a two-dimensional array of GaN pyramids are studied using scanning tunneling microscopy and local tunneling spectroscopy. This structure can be used as a test structure for the application of graphene as a flexible conductive transparent electrode in optoelectronics. Sagging of a graphene layer in the space between pyramids is found and the sagging value is estimated to be about 20% of the pyramid height of 1.1 μm. Local energy spectra show the change of the graphene electron energy spectrum due to the mechanical stress at sagging.

Numerical simulations of spatially non-uniform picosecond-range switching of high-voltage silicon diodes with technological imperfections have been performed. It is shown that spatially inhomogeneous distribution of process-induced deep-level centers that trigger ionization process easily provoke current localization. A fluctuation of concentration with a relative amplitude of 10% leads to almost complete localization of current. The switching time sharply decreases (from ∼100 ps to ∼10 ps) with the increase of the amplitude of the inhomogeneity and the decrease of its size.

Spin light-emitting diodes based on GaAs/InGaAs/AlGaAs heterostructures with a ferromagnetic CoPt injector have been fabricated and studied. To obtain stability of diodes at higher temperatures, heterostructures with three different combinations of a quantum well and barriers have been studied. A stable 2% circular polarization degree of electroluminescence was obtained at temperatures up to 300 K.

The circularly polarized electroluminescence from an InGaAs/GaAs light-emitting diode with a (Ga,Mn)Sb/n⁺GaAs tunnel junction was investigated in the temperature range of 10-300 K. The obtained polarization degree is believed to be driven by the spin injection of electrons from the valence band of ferromagnetic (Ga,Mn)Sb into the conduction band of n⁺GaAs. The temperature dependencies of the polarization characteristics are determined by the ferromagnetic properties of the (Ga,Mn)Sb layer. The room temperature circularly polarized emission is prospective for the fabrication of a spin light-emitting diode with an injector based on a diluted magnetic semiconductor.

In this paper a probe of an atomic force microscope (AFM) served as a detector of optical radiation. We investigated absorption of optical radiation in the visible range by commercially available Si and Si₃N₄ probes. It has been shown that the radiation in the far field is mainly absorbed in the probe tip. By scanning a laser beam with a diameter of ∼ 0.7 microns by the AFM probe, a lateral resolution of ∼ 1.5 microns was demonstrated. Numerical modeling of evanescent wave absorption by AFM probes showed enhancement of the absorption in the probes as compared with a flat surface. A Si₃N₄ probe more effectively absorbs the evanescent radiation.

The formation and approbation of the specialized nanoscalpel (NS) probes were carried out. The possibility of producing diffraction gratings on gold substrates for plasmonics applications was shown. The optimal lithography parameters were revealed by using NS probes. It was shown that NS probes allow improving the lithography results such as the depth and width of the incisions as compared to standard probes.

The series of InAlGaN LED structures containing two different quantum wells emitting at wavelengths of ∼ 430 nm and ∼ 490 nm was grown. The influence of the quantum wells order, thickness of the barrier between the wells and its doping level on the optical properties was studied by photo- and electro-luminescence measurements. It was found that the quantum well with longer-wavelength emission is preferable to be located farther from a player than the shorter-wavelength quantum well to obtain emission from both QWs. Variation of the thickness of the barrier between the QWs and its doping level allows controlling the intensity ratio of two emission peaks.

Investigation of the thermal annealing effect on Schottky barrier parameters and the leakage current of Ni/Au, Ni/Mo/Au and Mo/Au Schottky barriers on AlGaN/GaN heterostructures has been performed. Improvement of Schottky barrier parameters after annealing of the investigated metallization schemes was observed. Ni/Au and Mo/Au contacts drastically degrade after annealing at the temperatures higher than 400 °C, whereas the Ni/Mo/Au contact exhibits excellent parameters after 500 °C annealing (qϕ_b = 1.00 eV, n = 1.13 и I_leak = 5 μA).

A procedure for estimating an optical leakage of incoming radiation through a wide-bandgap subcell in a GaInP/GaInAs/Ge multijunction solar cell to photoactive layers of narrow-bandgap ones is proposed. A sequence for experimental determination of currents induced in a Ge subcell owing to an optical leakage or via a luminescent coupling is described.

We propose the contactless nondestructive method for determination of the carrier diffusion length in semiconductors and dielectrics. The method is based on optical generation of non-equilibrium carriers at one point of the studied sample and the laser interference measurement of their concentration at another point. When changing the distance between these points, a decrease in the carrier concentration is observed. It depends on the carrier diffusion length, which is determined by comparing the experimental and theoretical dependences of the probe signal on the divergence of the injector and probe beams. We have studied silicon samples protected by an insulator layer and without any covering. The method can be used in scientific research and the electronics industry.

In present work, the model and methodology for designing of arcuate arc-shallow MEMS with buckling was developed and tested. The efficiency of the model is confirmed experimentally. The result of the present survey is an increase of the efficiency of the exciting electrostatic comb drive MMG of high precision. The result of this research allows to reduce the control voltage and noise of a microgyroscope.

The boundary-value problem in the classical theory of elasticity for a core-shell nanowire with an eccentric parallelepipedal core of an arbitrary rectangular cross section is solved. The core is subjected to one-dimensional cross dilatation eigenstrain. The misfit stresses are given in a closed analytical form suitable for theoretical modeling of misfit accommodation in relevant heterostructures.