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A cycle of experimental investigations is carried out, specifically, the measurements and analysis of field dependences of the static magnetic susceptibility in samples of single-crystal SiC thin films grown on the (100), (110), and (111) surfaces of a Si single crystal by the method of the self-consistent substitution of atoms due to the chemical reaction of silicon with carbon-monoxide (CO) gas. As a result of investigations in SiC structures grown on Si(110) and Si(111), the appearance of two quantum effects is found in weak magnetic fields at room temperature. These effects are, first, the formation of hysteresis of the static magnetic susceptibility and, second, the generation of Aharonov–Bohm oscillations in the field dependences of the static magnetic susceptibility. The first effect is associated with the Meissner–Ochsenfeld effect and the second effect, with the presence of microdefects in the form of nanotubes and micropores formed during the synthesis of structures in them under the SiC layer. In the SiC structures grown on Si(100), these effects are not detected, which is related to a different mechanism of SiC formation on the Si(100) surface.

Over the past 30 years, there has been a great deal of interest in the use of terahertz (THz) radiation in various fields, such as security systems, communications, and spectroscopy. In addition, THz radiation is increasingly being used in practical medicine; in particular, the potential of THz irradiation for influencing metabolic reactions together with controlling the most important biochemical processes taking place in the human body has been demonstrated. In turn, this has stimulated the development of compact sources and detectors of THz and gigahertz (GHz) electromagnetic radiation on the basis of development of silicon optoelectronics and nanoelectronics. Silicon emitters with the ability to control THz and GHz frequency modulation are created, which enables their use for effective therapy of demyelinating diseases of the central nervous system.

A spectrometer based on silicon nanosandwiches (SNS) is proposed for problems of personalized medicine. SNS structures exhibit properties of terahertz (THz) emitter and receiver of the THz response of biological tissue. Measurements of the current-voltage curves of the SNS structure make it possible to analyze the spectral composition of the THz response of biological tissue and determine relative contributions of various proteins and amino acids contained in the structure of DNA oligonucleotides and the corresponding compounds. Evident advantages of the proposed method are related to the fact that the THz response can be directly obtained from living biological tissue and, hence, used for express analysis of the DNA oligonucleotides. Tests of several control groups show that the further analysis of the specific features of the spectral peaks of the SNS current-voltage curves is of interest for methods of personalized diagnostics and treatment., Comment: 4 pages, 8 figures

The ability to detect the terahertz (THz) emission from a silicon nanosandwich structure (Si-NS) is demonstrated with the silicon carbide nanostructure (SiC-NS) as a detector. Electrical response in longitudinal voltage of the detector was observed under the constant drain-source current (I ds(DET) ) of the detector.

The results of studying the quantum conductance staircase of holes in one−dimensional channels obtained by the split−gate method inside silicon nanosandwiches that are the ultra−narrow quantum well confined by the delta barriers heavily doped with boron on the n−type Si (100) surface are reported. Since the silicon quantum wells studied are ultra−narrow (~2 nm) and confined by the delta barriers that consist of the negative−U dipole boron centers, the quantized conductance of one−dimensional channels is observed at relatively high temperatures (T > 77 K). Further, the current−voltage characteristic of the quantum conductance staircase is studied in relation to the kinetic energy of holes and their sheet density in the quantum wells. The results show that the quantum conductance staircase of holes in p−Si quantum wires is caused by independent contributions of the one−dimensional (1D) subbands of the heavy and light holes; these contributions manifest themselves in the study of square−section quantum wires in the doubling of the quantum−step height (G0 = 4e2/h), except for the first step (G0 = 2e2/h) due to the absence of degeneracy of the lower 1D subband. An analysis of the heights of the first and second quantum steps indicates that there is a spontaneous spin polarization of the heavy and light holes, which emphasizes the very important role of exchange interaction in the processes of 1D transport of individual charge carriers. In addition, the field−related inhibition of the quantum conductance staircase is demonstrated in the situation when the energy of the field−induced heating of the carriers become comparable to the energy gap between the 1D subbands. The use of the split−gate method made it possible to detect the effect of a drastic increase in the height of the quantum conductance steps when the kinetic energy of holes is increased; this effect is most profound for quantum wires of finite length, which are not described under conditions of a quantum point contact. In the concluding section of this paper we present the findings for the quantum conductance staircase of holes that is caused by the edge channels in the silicon nanosandwiches prepared within frameworks of the Hall. This longitudinal quantum conductance staircase, Gxx, is revealed by the voltage applied to the Hall contacts, Vxy, to a maximum of 4e2/h. In addition to the standard plateau, 2e2/h, the variations of the Vxy voltage appear to exhibit the fractional forms of the quantum conductance staircase with the plateaus and steps that bring into correlation respectively with the odd and even fractional values.

The use of a dumbbell void model is adequate for quantifying hydraulic tortuosity from reservoir parameters. The dumbbell model of the void space involves the alternation of filtering channels of the rock with pores (macrocapillaries) and interporeal constrictions (microcapillaries). Hydraulic tortuosity is physically explained by the expansion of the flow lines of the filtration flow in the pores and contraction in the interporeal tubules. Residual water is confined mainly to clay particles that line the pore channels. Since the residual water is immobile, it leads to a narrowing of the open area of the pores and, consequently, to a specific decrease in hydraulic tortuosity.

Superconductivity of the sandwich’ S-Si-QW-S structures that represent the p-type high mobility silicon quantum wells confined by the nanostructured δ - barriers heavily doped with boron on the n-type Si (100) surface has been demonstrated in the measurements of the temperature and magnetic field dependencies of the resistance, thermo-emf, specific heat and magnetic susceptibility. The studies of the cyclotron resonance angular dependences, the scanning tunneling microscopy images and the electron spin resonance have shown that the nanostructured δ barriers consist of a series of alternating undoped and doped quantum dots, with the doped dots containing the single trigonal dipole centers, B+ - B-, which are caused by the negativeU reconstruction of the shallow boron acceptors, 2B0→B+ + B-. The temperature and magnetic field dependencies of the resistance, thermo-emf, specific heat and magnetic susceptibility are evidence of the high temperature superconductivity, Tc = 145 K, that seems to result from the transfer of the small hole bipolarons through these negative-U dipole centers of boron at the Si-QW – δ - barrier interfaces. The oscillations of the upper critical field and critical temperature vs magnetic field and temperature that result from the quantization of the critical current have been found using the specific heat and magnetic susceptibility techniques. The value of the superconductor energy gap, 0.044 eV, derived from the measurements of the critical temperature using the different techniques appeared to be practically identical to the data of the current-voltage characteristics and the local tunneling spectroscopy. The extremely low value of the hole effective mass in the ‘sandwich’ S-Si-QW-S structures that has been derived from the measurements of the SdH oscillations seems to be the principal argument for the bipolaronic mechanism of high temperature superconductor properties that is based on the coherent tunneling of bipolarons. The high frequency local phonon mode that is revealed with the superconductor energy gap in the infrared transmission spectra seems also to be responsible for the formation and the transfer of small hole bipolarons. The proximity effect in the S-Si-QW-S structure has been identified by the findings of the MAR processes and the quantization of the supercurrent. The value of the superconductor energy gap, 0.044 eV, appeared to be in a good agreement with the data derived from the oscillations of the conductance in normal state and of the zero-resistance supercurrent in superconductor state as a function of the bias voltage. These oscillations have been found to

We present the experimental data of the electric features of the silicon nanosandwichstructures obtained by silicon planar technology in the frameworks of the Hall geometry that represent the ultra-shallow silicon quantum well of 2 nm wide that are confined by delta-barrier heavily doped with boron, which create the edge channels used as the phase controllers of electric signals. The formation of the negative-U dipole boron centers, which appear to confine the edge channels, results in the effective mass dropping and corresponding reduction of the electron-electron interaction thereby giving rise to the macroscopic quantum phenomena at high temperatures up to room temperature. The phase control of the longitudinal conductance is observed by changing either the magnitude of the source-drain current or the voltage applied to the external gate of the silicon nanosandwiches within the quantum Faraday effect., 5 pages, 4 figures

The negative-U impurity stripes confining the edge channels of semiconductor quantum wells are shown to allow the effective cooling inside in the process of the spin-dependent transport, with the reduction of the electron-electron interaction. The aforesaid promotes also the creation of composite bosons and fermions by the capture of single magnetic flux quanta on the edge channels under the conditions of low sheet density of carriers, thus opening new opportunities for the registration of the quantum kinetic phenomena in weak magnetic fields at high temperatures up to the room temperature. As a certain version noted above we present the first findings of the high temperature de Haas-van Alphen, 300K, quantum Hall, 77K, effects as well as quantum conductance staircase in the silicon sandwich structure that represents the ultra-narrow, 2 nm, p-type quantum well (Si-QW) confined by the delta barriers heavily doped with boron on the n-type Si (100) surface., 11 pages, 9 figures. arXiv admin note: substantial text overlap with arXiv:1601.05975, arXiv:1207.4928

Highly effective treatment of patients with pulmonary pathologies, including pathology caused by a new type of coronavirus infection, is demonstrated, using terahertz (THz) irradiation from a silicon nanosandwich structure (SNS) that is caused by the quantum Faraday effect under the stabilized drain-source current conditions. It was shown that the early (on the first day) use of the THz irradiation made it possible to reduce the patient's stay in the intensive care unit as well as the duration of the patient's intubation and mechanical ventilation, to reduce the radiological and pharmacological load on the patient, and increase the chances of a favorable prognosis in patients with risk factors.

The phase controlled longitudinal conductance and the modulated phase shift of the THz electroluminescence spectrum are observed by varying the voltage applied to the external gates of the silicon nanosandwiches within the quantum Faraday effect.

The results of studying the quantum conductance staircase of holes in one-dimensional channels obtained by the split-gate method inside silicon nanosandwiches that are the ultra-narrow quantum well confined by the delta barriers heavily doped with boron on the n-type Si (100) surface are reported. Since the silicon quantum wells studied are ultra-narrow (~2 nm) and confined by the delta barriers that consist of the negative-U dipole boron centers, the quantized conductance of one-dimensional channels is observed at relatively high temperatures ( T >77 K). Further, the current-voltage characteristic of the quantum conductance staircase is studied in relation to the kinetic energy of holes and their sheet density in the quantum wells. The results show that the quantum conductance staircase of holes in p-Si quantum wires is caused by independent contributions of the one-dimensional (1D) subbands of the heavy and light holes. In addition, the field-related inhibition of the quantum conductance staircase is demonstrated in the situation when the energy of the field-induced heating of the carriers become comparable to the energy gap between the 1D subbands. The use of the split-gate method made it possible to detect the effect of a drastic increase in the height of the quantum conductance steps when the kinetic energy of holes is increased; this effect is most profound for quantum wires of finite length, which are not described under conditions of a quantum point contact. In the concluding section of this paper we present the findings for the quantum conductance staircase of holes that is caused by the edge channels in the silicon nanosandwiches prepared within frameworks of the Hall geometry. This longitudinal quantum conductance staircase, G xx , is revealed by the voltage applied to the Hall contacts, with the plateaus and steps that bring into correlation respectively with the odd and even fractional values.

The THz properties of the DNA oligonucleotides are identified by the deposition in the edge channels of the silicon nanostructures

Planar silicon nanostructures that are formed as a very narrow silicon quantum well confined by δ barriers heavily doped with boron are used to study the dielectric properties of DNA oligonucleotides deposited onto the surface of the nanostructures. The capacitance characteristics of the silicon nanostructures with oligonucleotides deposited onto their surface are determined by recording the local tunneling current–voltage characteristics by means of scanning tunneling microscopy. The results show the possibility of identifying the local dielectric properties of DNA oligonucleotide segments consisting of repeating G–C pairs. These properties apparently give grounds to correlate the segments with polymer molecules exhibiting the properties of multiferroics.

The possibility of identifying DNA oligonucleotides deposited onto the region of the edge channels of silicon nanostructures is considered. The role of various THz (terahertz) radiation harmonics of silicon nanostructures in the resonance response of oligonucleotides is analyzed. In particular, this makes it possible to compare single-stranded 100_ and 50_mer DNA oligonucleotides. A technique for the rapid identification of different oligonucleotides by measuring changes in the conductance and transverse potential difference of silicon nanostructures with microcavities, embedded in the edge channels for selecting THz radiation characteristics, is proposed.

The sulfur passivation of the semi-insulating GaAs bulk (SI GaAs) grown in an excess phase of arsenic is used to observe the transition from the Coulomb blockade to the weak localization regime at room temperature. The I–V characteristics of the SI GaAs device reveal nonlinear behavior that appears to be evidence of the Coulomb blockade process as well as the Coulomb oscillations. The sulfur passivation of the SI GaAs device surface results in enormous transformation of the I–V characteristics that demonstrate the strong increase of the resistance and Coulomb blockade regime is replaced by the electron tunneling processes. The results obtained are analyzed within frameworks of disordering SI GaAs surface that is caused by inhomogeneous distribution of the donor and acceptor anti-site defects which affects the conditions of quantum- mechanical tunneling. Weak localization processes caused by the preservation of the Fermi level pinning are demonstrated by measuring the negative magnetoresistance in weak magnetic fields at room temperature. Finally, the studies of the magnetoresistance at higher magnetic fields reveal the h/2e Aharonov–Altshuler–Spivak oscillations with the complicated behavior due to possible statistical mismatch of the interference paths in the presence of different microdefects.

Ultra-shallow p+–n junctions fabricated by the silicon planar technology based on the short-time nonequilibrium diffusion of boron from the gas phase into n-Si (100) substrates upon their preliminary oxidation and the opening of windows in SiO2 by electron lithography and reactive ion etching are examined. The electroand photoluminescence spectra measured in the study demonstrate emission in the range 1–1.6 µm, which is indicative of the presence of a high concentration of defects that probably appear as a result of the amorphizing effect of ions in the etching stage.

Our results demonstrate a new method for label-free, real-time oligonucleotide characterisation by their self-resonant modes, which are unique to their conformation and sequence. We anticipate that our assay will be used as a starting point for a more detailed investigation of the aforementioned mechanism, which can be used as a basis for oligonucleotide detection and analysis. Furthermore, this technique can be applied to improve existing modern genetics technologies., 6 pages, 3 figures

We present the first findings of the silicon vacancy related centers identified in the non-irradiated 6H-SiC nanostructure using the electron spin resonance (ESR) and electrically-detected (ED) ESR technique. This planar 6H-SiC nanostructure represents the ultra-narrow p-type quantum well confined by the δ-barriers heavily doped with boron on the surface of the n-type 6H-SiC(0001) wafer. The new EDESR technique by measuring the only magnetoresistance of the 6H-SiC nanostructure under the high frequency generation from the δ-barriers appears to allow the identification of the isolated silicon vacancy centers as well as the triplet center with spin state S = 1. The same triplet center that is characterized by the large value of the zero-field splitting constant D and anisotropic g-factor is revealed by the ESR (X-band) method. The hyperfine (HF) lines in the ESR and EDESR spectra originating from the HF interaction with the 14N nucleus seem to attribute this triplet center to the N-V Si defect.

Electron and hole cyclotron resonance at a frequency of 94 GHz is detected by a change in the intensity of photoluminescence lines whose positions are identical to those of dislocation luminescence lines D1 and D2 in single-crystal silicon and in heavily boron-doped silicon nanostructures on the Si (100) surface. The angular dependence of the spectrum of the optically detected cyclotron resonance corresponds to the tensor of the electron and hole effective mass in single-crystal silicon, and the resonance-line width indicates long carrier free-path times close to 100 ps. The results obtained are discussed within the framework of the interrelation of the electron-vibration coupling to charge and spin correlations in quasi-one-dimensional chains of dangling bonds in silicon.

We demonstrate a novel approach to the problem of THz emission and detection by quantum Faraday effect that manifests itself in conductance of topological edge channels of silicon nanosandwich-structures.

The results of investigation of electrically-detected electron paramagnetic resonance (EDEPR) and classical electron paramagnetic resonance (EPR) (X-band) for the identification of shallow and deep boron centers, NV Si defects, and isolated silicon vacancies (V Si), which are formed directly during the preparation of planar nanostructures under conditions of silicon-vacancy injection at the SiO2/n-6H-SiC interface without any subsequent irradiation, are presented. The prepared sandwich nanostructures are an ultra-narrow p-type quantum well, confined by δ barriers heavily doped with boron on an n-6H-SiC surface, which are self-ordered during pyrolytic-oxide deposition and subsequent short-time boron diffusion. The EDEPR data of point centers in sandwich nanostructures, prepared within the framework of Hall geometry, are recorded by measuring the field dependences of the magnetoresistance without an external cavity, microwave source and detector, due to the presence of microcavities embedded in the quantum-well plane and microwave generation under conditions of a stabilized source-drain current from δ barriers containing dipole boron centers. The obtained EDEPR spectra of the shallow and deep boron centers are analyzed using the data of EPR studies in 6H-SiC bulk crystals [10]. The EDEPR spectrum of the isolated silicon vacancy reveals both the negatively charged state V Si − (S = 3/2) and the neutral state in hexagonal (V Si(h)) and quasicubic (V Si(k1, k2)) states (S = 1). In turn, NV Si defects are detected not only by the EDEPR method at 77 K, but also through the use of a Bruker ELEXSYS E580 EPP spectrometer at 9.7 GHz, in a temperature range of 5–40 K. The EDEPR and EPR spectra recorded on the same sandwich nanostructure are virtually identical and correspond to the center in the triplet state with spin S = 1. The EPR spectrum, which is a lowintensity line doublet with a splitting value equal to ΔB = 237.6 mT, is observed in the background of the EPR spectrum from donors of nitrogen, the concentration of which in the n-6H-SiC initial sample was 5 × 1018 cm−3, whereas nitrogen donor centers are not revealed in the EDEPR spectrum because of total occupation by silicon vacancies inside the 6H-SiC sandwich nanostructure.

A method for determining the conductance matrix is analyzed to study the properties of silicon nanostructures fabricated within Hall geometry on an n-type Si(100) surface as ultra-narrow p-type silicon quantum wells bounded by δ barriers heavily doped with boron. Within the proposed approach, the total current flowing through the multiterminal silicon nanostructure is written in the matrix form as I = G · V, where I and V are the columns of currents and voltages for each of the N terminals, G is the N × N conductance matrix uniquely describing the conductance of the structure under study, taking into account the contribution of contact-area resistances. The high sensitivity of matrix elements to changes in the state of the silicon nanostructure surface under conditions of the precipitation of sodium-acetate solution containing single-strand synthetic oligonucleotides is demonstrated. The prospects of practical application of the results obtained in developing modern biosensors based on determining the conductance matrix of multiterminal semiconductor nanostructures are discussed.

The experimental data of the optical and electric features of the silicon nanosandwiches obtained by silicon planar technology in the frameworks of the Hall geometry are presented. Silicon nanosandwiches represent the ultra-shallow silicon quantum wells of 2nm wide that are confined by δ-barriers heavily doped with boron, which appear to be used as the phase invertors and modulators of optical THz spectra and electric signals. The negative-U dipole boron centers formation, which appear to confine the edge channels, results in the effective mass dropping and corresponding reduction of the electron-electron interaction thereby giving rise to the macroscopic quantum phenomena at high temperatures up to room temperature. The modulation phase shift of the THz electroluminescence spectrum and phase control of the longitudinal conductance are observed by changing either the magnitude of the source-drain current or the voltage applied to the external gates of the silicon nanosandwiches within the quantum Faraday effect.

We present manifestations of room temperature superconductivity in thin films fabricated of YBa2Cu3O7–δ (YBCO) on the substrate of NdGaO3 (110). We show that the static magnetic susceptibility measurements demonstrate the Meissner effect in weak magnetic fields at room temperature. In addition, the oscillations of the magnetic susceptibility are revealed in external magnetic field, which can be interpreted as the quantization of magnetic flux through inclusions, with superconducting domains around them and the observation of the field-dependent steps that seem to be of evidence the second-order phase transition of domains. The results obtained are in a good agreement with the data of tunneling I-V curves. Finally, we suggest few further experiments that could confirm our hypothesis.

We demonstrate a novel approach to the problem of express diagnostics based on THz spectral features of the breast cancer and THz emission and detection provided by the topological edge channels of silicon nanosandwichstructures.

The results of studying the characteristics of optical emission in various regions of quantum-confined silicon p +-n heterojunctions heavily doped with boron are analyzed. The results obtained allow one to conclude that near-infrared electroluminescence arises near the heterointerface between the nanostructured wide-gap silicon p +-barrier heavily doped with boron and n-type silicon (100), the formation of which included the active involvement of boron dipole centers.

The cyclotron resonance in semiconductor nanostructures is electrically detected for the first time without an external cavity, a source, and a detector of microwave radiation. An ultranarrow p-Si quantum well on an n-Si (100) surface confined by superconducting heavily boron-doped δ-shaped barriers is used as the object of investigation and provides microwave generation within the framework of the nonstationary Josephson effect. The cyclotron resonance is detected upon the presence of a microcavity, which is incorporated into the quantum-well plane, by measuring the longitudinal magnetoresistance under conditions of stabilization of the source-drain current. The cyclotron-resonance spectra and their angular dependences measured in a low magnetic field identify small values of the effective mass of light and heavy holes in various 2D subbands due to the presence of edge channels with a high mobility of carriers.

Triplet center with spin state S = 1 is detected in the EPR spectrum of the self-assembled 6H SiC nanostructure obtained by non-equilibrium boron diffusion into the n-type 6H SiC epitaxial layer (EL) under conditions of the controlled injection of the silicon vacancies at the temperature of T = 900°C. From the analysis of the angular dependences of the EPR spectrum and the numerical diagonalization of the spin Hamiltonian, the value of the zero-field splitting constant D and g-factor are found to be D = 1140•10-4см-1 and gpar = 1.9700, gper = 1.9964. Based on the hyperfine (hf) structure of the defect originating from the hf interaction with one 14N nuclei, the large value of the zero-field splitting constant D and technological conditions of the boron diffusion into the n-type 6H SiC EL, the triplet center is tentatively assigned to the defect center consisting of nitrogen atom and silicon vacancy.

The negative-U impurity stripes confining the edge channels of semiconductor quantum wells are shown to allow the effective cooling inside in the process of the spin-dependent transport. The aforesaid promotes also the creation of composite bosons and fermions by the capture of single magnetic flux quanta on the edge channels under the conditions of low sheet density of carriers, thus opening new opportunities for the registration of the quantum kinetic phenomena in weak magnetic fields at high temperatures up to the room temperature. As a certain version noted above we present the first findings of the high temperature de Haas-van Alphen, 300K, and quantum Hall, 77K, effects in the silicon sandwich structure that represents the ultra-narrow, 2 nm, p-type quantum well (Si-QW) confined by the delta barriers heavily doped with boron on the n-type Si (100) surface. These data appear to result from the low density of single holes that are of small effective mass in the edge channels of p-type Si-QW because of the impurity confinement by the stripes consisting of the negative-U dipole boron centers which seems to give rise to the efficiency reduction of the electron-electron interaction., Comment: 19 pages, 7 figures

We present the findings of the optically detected magnetic resonance technique (ODMR), which reveal single point defects in the ultra-narrow silicon quantum wells (Si-QW) confined by the superconductor δ-barriers. This technique allows the ODMR identification without application of an external cavity, as well as a high frequency source and recorder, and with measuring the transmission spectra within the frameworks of the excitonic normal-mode coupling caused by the microcavities embedded in the Si-QW plane. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

One of the best candidate on the role of the THz optoelectronic pairs appears to be the high mobility p -type silicon quantum well (Si-QW), 2 nm, confined by the δ-barriers heavily doped with boron on the n -type Si (100) surface. The δ-barriers heavily doped with boron are already shown to exhibit the high temperature superconductor properties, Tc = 145 K, 2Δ = 44 meV and Hc 2 = 0.22 T. This Si-QW confined by the superconductor δ-barriers is a basis of the sandwich nanostructure device that is used to register the Shapiro steps and the Fiske steps by measuring the Josephson CV characteristics. The Josephson GHz and THz emission is controlled, for the first time, by stabilizing the drain-source current and by varying the top gate voltage. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present the first findings of the new electrically detected electron spin resonance technique (EDESR) which reveal single point defects in the ultra-narrow silicon quantum wells (Si-QW) confined by the superconductor δ-barriers. This technique allows the ESR identification without the application of the external cavity as well as the high frequency (hf) source and recorder, with measuring the only magnetoresistance caused by the hf emission from the δ-barriers in the presence of the microcavity embedded in the Si-QW plane. The new resonant positive magnetoresistance data are interpreted here in terms of the interference transition in the diffusive transport of free holes respectively between the weak antilocalization regime in the range of magnetic fields far from the ESR of a paramagnetic point defect located inside or near the conductive channel and the weak localization regime in the range of magnetic fields corresponding to the ESR of that defect. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The circularly polarized electroluminescence (CPEL) from silicon nanostructures which are the p-type ultra-narrow silicon quantum well (Si-QW) confined by {\delta}-barriers heavily doped with boron, 5 10^21 cm^-3, is under study as a function of temperature and excitation levels. The CPEL dependences on the forward current and temperature show the circularly polarized light emission which appears to be caused by the exciton recombination through the negative-U dipole boron centers at the Si-QW {\delta}-barriers interface.

Spin-dependent transport of holes is studied in silicon nanosandwiches on an n-Si (100) surface which are represented by ultranarrow p-Si quantum wells confined by δ-barriers heavily doped with boron. The measurement data of the longitudinal and Hall voltages as functions of the top gate voltage without an external magnetic field show the presence of edge conduction channels in the silicon nanosandwiches. An increase in the stabilized source-drain current within the range 0.25–5 nA subsequently exhibits the longitudinal conductance value 4e2/h, caused by the contribution of the multiple Andreev reflection, the value 0.7(2e2/h) corresponding to the known quantum conductance staircase feature, and displays Aharonov-Casher oscillations, which are indicative of the spin polarization of holes in the edge channels. In addition, at a low stabilized source-drain current, due to spin polarization, a nonzero Hall voltage is detected which is dependent on the top gate voltage; i. e., the quantum spin Hall effect is observed. The measured longitudinal I–V characteristics demonstrate Fiske steps and a negative differential resistance caused by the generation of electromagnetic radiation as a result of the Josephson effect. The results obtained are explained within a model of topological edge states which are a system of superconducting channels containing quantum point contacts transformable to single Josephson junctions at an increasing stabilized source-drain current.

Measurements of the field and temperature dependences of static magnetic susceptibility demonstrate de Haas-van Alphen oscillations at high temperatures and low magnetic fields in sandwich nanostructures, which are represented by an ultranarrow p-type CdF2 quantum well confined by δ barriers heavily doped with boron on the surface of an n-type CdF2 crystal. The temperature dependences of the de Haasvan Alphen oscillation amplitudes indicate a small value of the effective mass of two-dimensional holes, as a result of which, the strong field assumption, μB ≫ 1, is fulfilled at high temperatures. It is for the first time that a periodic variation in the de Haas-van Alphen oscillation frequency is detected and is accompanied by a diamagnetic response as temperature is increased. This phenomenon manifests itself as synchronous temperature oscillations of the density and effective mass of two-dimensional holes as a result of the mesoscopic properties of δ barriers.

We present the findings for the fractional quantum conductance of holes that is caused by the edge channels in the silicon nanosandwich prepared within frameworks of the Hall geometry. This nanosandwich represents the ultra-narrow p-type silicon quantum well (Si-QW), 2 nm, confined by the {\delta}-barriers heavily doped with boron on the n-type Si (100) surface. The edge channels in the Si-QW plane are revealed by measuring the longitudinal quantum conductance staircase, Gxx, as a function of the voltage applied to the Hall contacts, Vxy, to a maximum of 4e2/h. In addition to the standard plateau, 2e2/h, the variations of the Vxy voltage appear to exhibit the fractional form of the quantum conductance staircase with the plateaus and steps that bring into correlation respectively with the odd and even fractional values.

The dependences of the longitudinal resistance and the static magnetic susceptibility on the magnetic field applied perpendicularly to the plane of an ultranarrow silicon quantum well confined by δ barriers heavily doped with boron demonstrate the high-temperature Shubnikov-de-Haas and de-Haas-van-Alphen oscillations in low magnetic fields. The results are indicative of the implementation of the high-field approximation μB ≫ 1 under these conditions due to the small effective mass of two-dimensional heavy holes, which is confirmed by measurements of temperature dependences of the de-Haas-van-Alphen oscillations.

We present the first findings of the new electrically- and optically-detected magnetic resonance technique [ED electron spin resonance (EDESR) and (ODMR)] which reveal single point defects in the ultra-narrow silicon quantum wells (Si-QW) confined by the superconductor δ-barriers. This technique allows the ESR identification without the application of the external cavity as well as a high frequency source and recorder, with measuring the only magnetoresistance (EDESR) and transmission (ODMR) spectra within frameworks of the excitonic normal-mode coupling (NMC) caused by the microcavities embedded in the Si-QW plane. The new resonant positive magnetoresistance data are interpreted here in terms of the interference transition in the diffusive transport of free holes respectively between the weak antilocalization regime in the region far from the ESR of a paramagnetic point defect located inside or near the conductive channel and the weak localization regime in the nearest region of the ESR of that defect.

We present the findings of spin-dependent single-hole and pair-hole transport in plane and across the p-type high mobility silicon quantum wells (Si-QW), 2 nm, confined by the superconductor δ-barriers on the n-type Si (100) surface. The oscillations of the conductance in normal state and the zero-resistance supercurrent in superconductor state as a function of the top gate voltage are found to be correlated by on- and off-resonance tuning the two-dimensional levels of holes in Si-QW with the Fermi energy in the superconductor δ-barriers. The SIMS and STM studies have shown that the δ-barriers heavily doped with boron, 5 × 1021 cm–3, represent really alternating arrays of silicon empty and doped dots, with dimensions restricted to 2 nm. This concentration of boron seems to indicate that each doped dot located between empty dots contains two impurity atoms of boron. The EPR studies show that these boron pairs are the trigonal dipole centres, B+ - B–, that contain the pairs of holes, which result from the negative -U reconstruction of the shallow boron acceptors, 2B0 => B+ - B–. The electrical resistivity, magnetic susceptibility and specific heat measurements demonstrate that the high density of holes in the Si-QW (> 1011 cm–2) gives rise to the high temperature superconductor properties for the δ-barriers. The value of the superconductor energy gap obtained is in a good agreement with the data derived from the oscillations of the conductance in normal state and of the zero-resistance supercurrent in superconductor state as a function of the bias voltage. These oscillations appear to be correlated by on- and off-resonance tuning the two-dimensional subbands of holes with the Fermi energy in the superconductor δ-barriers. Finally, the proximity effect in the S-Si-QW-S structure is revealed by the findings of the quantization of the supercurrent and the multiple Andreev reflection (MAR) observed both across and along the Si-QW plane thereby identifying the spin transistor effect.

Tunneling current-voltage (I-V) characteristics and temperature dependences of static magnetic susceptibility and specific heat of the CdB x F2 − x /p-CdF2-QW/CdB x F2 − x planar sandwich structures formed on the surface of an n-CdF2 crystal have been studied in order to identify superconducting properties of the CdB x F2 − x δ barriers confining the p-type CdF2 ultranarrow quantum well. Comparative analysis of current-voltage (I-V) characteristics and conductance-voltage dependences (measured at the temperatures, respectively, below and above the critical temperature of superconducting transition) indicates that there is an interrelation between quantization of supercurrent and dimensional quantization of holes in the p-CdF2 ultranarrow quantum well. It is noteworthy that detection of the Josephson peak of current in each hole subband is accompanied by the appearance of the spectrum of the multiple Andreev reflection (MAR). A high degree of spin polarization of holes in the edge channels along the perimeter of the p-CdF2 ultranarrow quantum well appears as a result of MAR and makes it possible to identify the quantum spin Hall effect I-V characteristics; this effect becomes pronounced in the case of detection of nonzero conductance at the zero voltage applied to the vertical gate in the Hall geometry of the experiment. Within the energy range of superconducting gap, the I-V characteristics of the spin transistor and quantum spin Hall effect are controlled by the MAR spectrum appearing as the voltage applied to the vertical gate is varied. Beyond the range of the superconducting gap, the observed I-V characteristic of the quantum spin Hall effect is represented by a quantum conductance staircase with a height of the steps equal to e 2/h; this height is interrelated with the Aharonov-Casher oscillations of longitudinal and depends on the voltage applied to the vertical gate.

Planar CdBxF2-x - p-CdF2 - CdBxF2-x sandwich nanostructures prepared on the surface of the n-type CdF2 bulk crystal are studied to register the spin transistor and quantum spin Hall effects. The current-voltage characteristics of the ultra-shallow p+-n junctions verify the CdF2 gap, 7.8 eV, and the quantum subbands of the 2D holes in the p-type CdF2 quantum well confined by the CdBxF2-x delta-barriers. The temperature and magnetic field dependencies of the resistance, specific heat and magnetic susceptibility demonstrate the high temperature superconductor properties for the CdBxF2-x delta-barriers. The value of the superconductor energy gap, 102.06 meV, determined by the tunneling spectroscopy method appears to be in a good agreement with the relationship between the zero-resistance supercurrent in superconductor state and the conductance in normal state at the energies of the 2D hole subbands. The results obtained are evidence of the important role of the multiple Andreev reflections in the creation of the high spin polarization of the 2D holes in the edged channels of the sandwich device. The high spin hole polarization in the edged channels is shown to identify the mechanism of the spin transistor and quantum spin Hall effects induced by varying the top gate voltage, which is revealed by the first observation of the Hall quantum conductance staircase., Comment: 5 pages, 9 figures

The tunneling spectroscopy is used for studying the hole transport in a sandwich nanostructure of the superconductor-ultra-narrow-self-assembled-p-silicon-quantum-well (Si-QW)-superconductor type on the n-Si (100) surface; the quantum well’s width is less than the coherence length and the Fermi wave-length. The high-resolution tunneling I–V characteristics display the supercurrent quantization, the characteristics of which depend on the positions of the dimensional-quantization levels for holes in the Si-QW. The correlation in the tunneling of single holes and Cooper pairs manifests itself in identical oscillations of the I–V characteristics for the supercurrent at T < T c and the conductivity at T > T c . In addition to the Josephson effect, the forward and reverse I–V characteristics for the first time reveal the processes of multiple Andreev reflection of two-dimensional holes in the Si-QW, which cause the microscopic mechanism responsible for the superconducting proximity effect. The investigation of the two-dimensional hole’s conductivity in the Si-QW plane indicates the presence of coherent tunneling under conditions of the spin-dependent multiple Andreev reflection between the superconducting δ] barriers confining it.

Superconducting properties of silicon sandwich nanostructures on the n-Si (100) surface, which represent the ultra-narrow p-type silicon quantum wells confined by heavily boron-doped δ barriers, manifest themselves in the measurements of the temperature and field dependences of resistivity, thermopower, heat capacity, and static magnetic susceptibility. The cyclotron-resonance, scanning-tunneling-microscopy, and ESR data identify the presence of the single trigonal negative-U dipole boron centers in nanostructured δ barriers B +-,B −, which are formed due to the reconstruction of shallow boron acceptors, 2B 0 ⇒ B + + B −. The obtained results indicate that these negative-U centers are responsible for the transport of small-radius hole bipolarons, which is likely the basis of the mechanism of high-temperature superconductivity with T C = 145 K. The superconductor-gap value of 0.044 eV determined from the measurements of the critical temperature using the above techniques is almost identical to the data on the tunneling spectroscopy and direct record of tunneling I–V characteristics. The quantization of the superconductive characteristics for silicon sandwich nanostructures manifests itself in the temperature and field dependences of the heat capacity and static magnetic susceptibility, which show the oscillations of the second critical field and critical temperature arising due to the supercurrent quantization.

A study of CdB x F2 − x /p-CdF2/CdB x F2 − x planar sandwich structures fabricated on n-CdF2 crystal surface was carried out in order to obtain the spin-transistor effect at room temperature. Features related to the band gap of CdF2 (7.8 eV) along with those related to the spectrum for two-dimensional (2D) hole subbands in p-CdF2 quantum well (QW) were observed in the current-voltage characteristics for ultrashallow p +-n junctions. The results obtained demonstrate the important role for 2D hole subbands in the mechanism of the “proximity effect” that appears due to Andreev’s reflection in sandwich structures consisting of a narrow QW confined between superconducting barriers. Resonance behavior for the longitudinal voltage in a weak magnetic field normal to the plane of the p-CdF2 QW gives evidence for high degree of spin polarization for 2D holes. Analysis of the dependences for the 2D-hole-gas conductance on the magnitude and direction of the magnetic field normal to the plane of the p-CdF2 QW reveals anti-crossings for Zeeman sublevels in the singlet ground state and triplet excited state of boron dipole centers, responsible for the spin polarization of 2D holes in edge channels in the p-CdF2 QW. The high degree of spin polarization for 2D holes in edge channels in the p-CdF2 QW identifies the mechanism underlying spin-transistor I-V characteristics observed upon the variation of the gate voltage, which controls the magnitude of Bychkov-Rashba’s spin-orbit coupling.

We present the findings of spin-dependent single hole and pair-hole transport across the p-type high mobility silicon quantum well (Si-QW) confined by the superconductor delta-barriers on the n-type Si (1 0 0) surface. The oscillations of the conductance in normal state and the zero-resistance supercurrent in superconductor state as a function of the bias voltage are found to be correlated by on- and off-resonance tuning the two-dimensional subbands of holes with the Fermi energy in the superconductor barriers.

We present the first findings of the spin transistor effect caused by the Rashba gate-controlled ring embedded in the p-type self-assembled silicon quantum well that is prepared on the Si (100) surface. The coherence and phase sensitivity of the spin-dependent transport of holes are studied by varying the value of the external magnetic field and the gate voltage that are perpendicular to the plane of the double-slit ring. Firstly, the quantum scatterers connected to two one-dimensional leads and the quantum point contact inserted in the one of the arms of the double-slit ring are shown to define the amplitude and the phase of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations. Secondly, the amplitude and phase sensitivity of the 0.7 feature of the hole quantum conductance staircase revealed by the quantum point contact inserted are found to result from the interplay of the spontaneous spin polarization and the Rashba spin-orbit interaction., 2 pages, 2 figures, presented at the 5th International Conference on Strongly Correlated Electron Systems, SCES'05, Vienna, Austria, 26-30 July, 2005

Boron diffusion and the vapor-phase deposition of silicon layers are used to prepare ultrashallow p+-n junctions and p+-Si-n-CdF2 heterostructures on an n-CdF2 crystal surface. Forward portions of the I–V characteristics of the p+-n junctions and p+-Si-n-CdF2 heterojunctions reveal the CdF2 band gap (7.8 eV), as well as allow the identification of the valence-band structure of cadmium fluoride crystals. Under conditions in which forward bias is applied to the p+-Si-n-CdF2 heterojunctions, electroluminescence spectra are measured for the first time in the visible spectral region.