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Using density functional calculations, we elucidate the interaction between magnons and phonons on Fe(001) and O/Fe(001) surfaces. The effective Heisenberg exchange parameters between neighbor sites (Ji) were derived by fitting the ab initio spin spiral dispersion relation to a classical Heisenberg model. In bulk Fe, J5b has a larger amplitude than J2b-J4b. Surface magnons were softer on the Fe(001) surface than in bulk, but were strengthened on the O/Fe(001) surface through strong interactions between the O and Fe atoms. The four calculated high-energy phonon modes of O/Fe(001) excellently agreed with the experimental measurements. The J2 in O/Fe(001) decreased significantly with increasing phonon amplitude. Phonon-magnon coupling occurred more easily on O/Fe(001) than on Fe(001). The softening of the magnon on the O/Fe(001) with phonon amplitude was attributed to the reduced amplitude of longitudinal excitations. Magnetic moment of the Fe atom of the second layer (Fe2) was especially sensitive to phonon amplitude, regardless of the motion direction of the Fe2 atoms. [ABSTRACT FROM AUTHOR]

The effects of parabolic and shifted parabolic potentials on centred hydrogenic impurity-related binding energies are studied. This is theoretically achieved by solving the Schrödinger equation within the effective mass approximation. The hydrogenic impurity situates in the core of a spatially constant electrostatic potential, surrounded by a shell material which has either an intrinsic parabolic potential or shifted parabolic potential. For a given outer radius of the shell, the parabolic potential enhances binding energies (with greater enhancement for small radii of the core), while the shifted parabolic potential dwindles binding energies for small cores, and increases the binding energies for larger cores. An increase in the spatially invariant potential in the core results in reduced binding energies, with appreciable decrement occurring in core–shell structures that have wider cores. [ABSTRACT FROM AUTHOR]

In the present paper, we have reported the effect of molar concentration of Mg salt on physical properties of MgSe thin films deposited by chemical bath deposition process. The MgSe thin films have been characterized for their structural, morphological and optical studies. We have observed that the films are nanocrystalline in nature with cubic lattice. The optical band gap energy of MgSe is changed from 2.82 to 2.65 eV depending on Mg ion concentration in deposition bath. The electrical resistivity of MgSe film varies from 56 × 10 to 41 × 10 Ω cm depending on Mg ion concentration in reaction bath. The thermo-emf measurement has confirmed p-type conductivity of MgSe. [ABSTRACT FROM AUTHOR]

Some electronic parameters such as ideality factor, barrier height, series resistance and interface state densities of the Au/ p-InP Schottky barrier diodes with 100 and 200 μm diameter contacts have been investigated. We have calculated electronic parameters of these two diodes and compared using experimental forward bias current-voltage ( I- V) and reverse bias capacitance-voltage measurements at room temperature. The values of ideality factor and barrier height for the 100 and 200 μm diameter diodes have been obtained as 1.07, 0.84 and 1.08, 0.80 eV, respectively. In addition, we have calculated interface state density ( N) as a function of energy distribution ( E- E) of these diodes and compared them. The energy distribution of interface states density has been determined from the forward bias I- V characteristics by taking into account the bias dependence of the effective barrier height. Density of interface states in the considered energy range are in close agreement with values obtained for 100 and 200 μm diameter Au/ p-InP. [ABSTRACT FROM AUTHOR]

We calculate the mobility of the two-dimensional electron gas as realized in (110) AlAs quantum wells at zero temperature. In this structure the mass is strongly anisotropic which gives rise to an anisotropic mobility. By using a theoretical approach developed by Tokura [Phys. Rev. B 58, 7151 (1998)] we numerically calculate the anisotropic mobility. We study impurity scattering in quantum wells having an ellipsoidal Fermi surface. We find that increasing the electron density and/or the well width results in reduction of the anisotropy of the mobility while the anisotropy in the scattering time is increased. A strong dependence of the mobility anisotropy on the impurity position is predicted. Excellent agreement with a recently published experimental result is found under the assumption that impurities are located at the edge of the quantum well. [ABSTRACT FROM AUTHOR]

A theoretical and numerical analysis of the transmission of phase-modulated laser pulses through a thin film with excitonic nonlinearity is performed. It is shown that, by choosing the modulation law, one can efficiently control the optical nonlinearity of the film down to the inversion of the sign of nonlinearity. [ABSTRACT FROM AUTHOR]

The subband structure and occupation in the triangular quantum well at Al xGa1− xN/GaN heterointerfaces have been investigated by means of temperature dependent Shubnikov–de Haas (SdH) measurements at low temperatures and high magnetic fields under illumination. After the illumination of the heterostructures, the total two-dimensional electron gas concentration increases, and the SdH oscillation amplitudes are enhanced when there is no additional subband occupation. It is also found that the energy separation between the subbands decreases after the illumination. We suggest that the illumination decreases the electric field and thus weakens the quantum confinement of the triangular quantum well at Al xGa1− xN/GaN heterointerfaces. The GaN layer is thought to be the primary contributor of the excited electrons by the illumination. [ABSTRACT FROM AUTHOR]

Within the density functional theory, ab initio calculations of the electronic structure and magnetic properties of the (110) interface between the NiMnSb alloy and GaAs in dependence on configuration of contact atoms are carried out. It is found that two out of six possible atomic configurations of the interface exhibit a high degree of spin polarization, which attains 100% for one of the interfacial structures studied here. It is shown that contacts with a high degree of spin polarization are the most stable with an adhesion energy of about 1.3 J/m2. [ABSTRACT FROM AUTHOR]

Emission-voltage characteristics and frequency dependences of the luminescence intensity of electroluminescent capacitors on the basis of the ZnS:(Cu,Al) phosphor are studied. The effect of X-ray radiation (17 keV) on the high-resistivity GaAs layers obtained by three methods is studied. The possibility to develop the detectors of the ionizing radiation with optical reading of information with the use of the GaAs/ZnS structures is shown using a mathematical simulation. It is noted that the most promising material for the development of the solid-state image converters is GaAs:Cr obtained by diffusion of Cr from the deposited layer. [ABSTRACT FROM AUTHOR]

The quantum theory of the accumulation layer for n-type InN crystals is developed. The Coulomb interaction and the exchange interaction in the Kohn-Sham local density approximation is considered. The applicability of the theory is demonstrated by using recent literature data. The approach developed provides more solid data on the accumulation layer parameters. [ABSTRACT FROM AUTHOR]

The photorefractive effect that is nonlinear with respect to the pump power is studied. The physical phenomena responsible for such a nonlinearity are analyzed. The features of the transport electronic parameters of semiconductors are considered for the nonlinear photorefractive effect. [ABSTRACT FROM AUTHOR]

The N-Al0.27Ga0.73N/GaN High Electron Mobility Transistors (HEMTs) with different gate lengths L g (ranging from 170 nm to 0.5 μm) and gate widths W s (ranging from 100 to 1200 μm) have been studied. The S parameters have been measured; these parameters have been used to determine the current-gain cutoff frequency f t, the maximum oscillation frequency fmax, and the power gain MSG/MAG and Mason’s coefficients were investigated in the frequency range from 10 MHz to 67 GHz in relation to the gate length and gate width. It was found that the frequencies f t and fmax attain their maximum values of f t = 48 GHz and fmax = 100 GHz at L g = 170 nm and W g = 100 μm. The optimum values of W g and output power P out of the basic transistors have been determined for different frequencies of operation. It has also been demonstrated that the 170 nm Al0.27Ga0.73N/GaN HEMT technology provides both good frequency characteristics and high breakdown voltages and is very promising for high-frequency applications (up to 40 GHz). [ABSTRACT FROM AUTHOR]

We describe experiments investigating the quality of ohmic contacts to both bulk GaN and to III-nitride heterostructures. Titanium-based contacts were investigated to assess the role of intermixing and surface impurities for contact formation to n-type GaN. Direct contact to the two-dimensional electron gas in GaN/AlGaN heterostructures was also studied. These contacts were made by photochemical etching of the samples to expose the heterointerface. It was observed that even in the latter case contact annealing leads to a lower contact resistance by consuming surface contaminants and promoting beneficial interfacial reactions. Various passivation techniques were tried to reduce surface leakage current between contact pads and PECVD-deposited silicon nitride was found to be the best material for this application. [ABSTRACT FROM AUTHOR]

We have studied the magnetotransport properties of p-InMnAs layers in strong (up to 30 T) pulsed magnetic fields. The p-InMnAs layers were obtained by laser plasma deposition with subsequent annealing by radiation of a pulsed ruby laser. Under anomalous Hall effect conditions in a strong magnetic field (above 20 T), the Hall resistance in the paramagnetic region of temperatures is greater than that in the ferromagnetic region (below 40 K). It has also been established that, at helium temperatures, the negative magnetoresistance exhibits saturation in a field of about 10 T, whereas the anomalous Hall effect is saturated at about 2 T. At T ≈ 4 K, the resistance in a field of 10 T exhibits a more than tenfold decrease. The results are explained by a mesoscopically inhomogeneous distribution of the acceptor (Mn) impurity, a local ferromagnetic transition, and a percolation character of the conductivity of p-InMnAs films in a state close to the insulator-metal phase transition. The characteristic scale of magnetoelectric inhomogeneity in the system is evaluated based on an analysis of mesoscopic fluctuations of the nondiagonal component of the magnetoresistance tensor. [ABSTRACT FROM AUTHOR]

A nonmonotonic behavior of band bending φ S as a function of cesium coverage ϑ on the Cs/GaAs(001) surface is observed in the form of several maxima and minima. This behavior indicates the formation of the quasi-discrete spectrum of the adatom-induced electronic surface states. The hysteresis of the φ S(ϑ) dependence under adsorption and subsequent thermodesorption of cesium indicates the metastability of the Cs/GaAs(001) system. [ABSTRACT FROM AUTHOR]

The pattern-equation method is generalized for solution of the problem of scattering by layered inhomogeneous bodies. The algorithm of the method and calculated scattering patterns for bodies of various geometries are presented. The convergence rate of the numerical algorithm is demonstrated for bodies of various dimensions, and the method is compared to other numerical techniques of solution of the considered problem. [ABSTRACT FROM AUTHOR]

High-temperature, high-power, and continuous-wave (CW) operation of quantum-cascade lasers with 35 active/injector stages at λ∼8.85 μm above room temperature is achieved without using a buried heterostructure. At this long wavelength, the use of a wider ridge waveguide in an epilayer-down bonding scheme leads to a superior performance of the laser. For a high-reflectivity-coated 21 μm×3 mm laser, the output power of 237 mW and the threshold current density of 1.44 kA/cm2 at 298 K under CW mode are obtained with a maximum wall-plug efficiency of 1.7%. Further improvements were observed by using a 4-mm-long cavity. The device exhibits 294 mW of output power at 298 K and it operates at a high temperature, even up to 358 K (85°C). The full widths at half-maximum of the laser beam in CW operation for the parallel and the perpendicular far-field patterns are 25°and 63°, respectively. [ABSTRACT FROM AUTHOR]

Using the Hall method, regularities of Te doping of GaSb grown by the Czochralski method and by liquid-phase epitaxy (LPE) are studied. Optimum epitaxial conditions that enable the growth of Te-doped GaSb layers with higher carrier mobilities than the bulk Czochralski-grown GaSb are determined. Possibilities of improvement of output parameters of photoconverters obtained by diffusion of Zn into n-GaSb from the gas phase and by LPE are discussed. [ABSTRACT FROM AUTHOR]

The pseudomorphic AlGaAs/InGaAs/AlGaAs heterostructure δ-doped with silicon on both sides and used for fabrication of high-power transistors is optimized to obtain a high concentration n s and mobility of two-dimensional electron gas in the quantum well ( n s ≈ 3 × 1012 cm−2). Electrical and structural characteristics of the samples grown by molecular-beam epitaxy with various doping levels are studied. It is shown that the mobility and concentration of electrons varies as doping level is increased and the subbands of dimensional quantization are sequentially filled. In order to analyze the distribution of electrons in subbands of the heterostructure, the Shubnikov-de Haas oscillations at the liquid helium temperature were studied. The quality of the heterostructure layers was assessed using the method of X-ray diffraction. The data of photoluminescence spectroscopy are in good agreement with the results of calculations of the band structure. [ABSTRACT FROM AUTHOR]

Using the method of atomic force microscopy, complex studies of the profile, potential distribution φ( x, y), and distributions of the phase contrast of the surface of n-GaAs subjected to various types of chemical treatment are carried out. The distribution of the potential and phase contrast at a microlevel, in general, correlates with the profile character. The surface treated in the solution H2SO4: H2O = 1: 10 is characterized by a high degree of nonuniformity with an average roughness of the main profile Δ h≈ 10 nm. A considerable part of the surface is covered by hills 20–60 nm in height and 100–500 nm in diameter forming a specific substructure, which correspond to potential jumps as large as 50–60 mV against a general background of 0.77–0.80 V. At a nanolevel, correlation between the profile and phase contrast is clearly pronounced, but no correlation is found between the profile and potential distribution. Treatment of the surface of n-GaAs in a concentrated aqueous NH4OH solution leads to a decrease in the value of φ( x, y) by ∼0.2 V, and in its roughness by more than an order of magnitude (∼0.75 nm). The distribution of the profile and phase contrast over the surface is close to the ideal Gaussian distribution for relatively small areas of the surface (200 × 200 nm2). As the area increases, deviation from the Gaussian distribution becomes substantial because of smooth variation in the potential over the contact area. Conservation of the Gaussian character of the surface profile and a simultaneous rise in the average level of the roughness with an increase in the analyzed area indicates the fractal mechanism of formation of the surface profile. [ABSTRACT FROM AUTHOR]

Morphological and optical (with reflection spectra in the range of 200–750 nm, transmission spectra in the range of 2–25 μm, and ellipsometry) studies were performed for AlN films that had a thickness of 2–3 μm and were obtained by the method of high-frequency magnetron sputtering of an aluminum target in a gas mixture of Ar and N2 (1: 3) with deposition onto single-crystal n-Si (100) substrates with a resistivity of 20–60 Ω cm. It is shown that the films are dense and transparent; they are amorphous with crystalline grains and can be used efficiently in thin-film technology for fabrication of modern microelectronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Based on the measurements of current-voltage and capacitance-voltage characteristics and deep-level transient spectroscopy, comparison of the concentration of deep-level centers and conductivity of the channel of the AlGaN/GaN heterostructures grown by molecular beam epitaxy with the use of ammonia as the nitrogen source is carried out. Two types of defects with deep levels are revealed. One type is presumably associated with point defects localized near dislocations, and the other type is associated with the dislocations themselves. An increase in the concentration of the centers with deep levels correlates with an increase in the channel resistivity. The density of the deep-level centers can attain values of ∼1013 cm−2 and lead to compensation of the electron channel at the heterointerface. [ABSTRACT FROM AUTHOR]

A self-consistent calculation of the density of states and the spectral density function is performed in a two-dimensional spin-polarized hole system based on a multiple-scattering approximation. Using parameters corresponding to GaMnAs thin layers, a wide range of Mn concentrations and hole densities have been explored to understand the nature, localized or extended, of the spin-polarized holes at the Fermi level for several values of the average magnetization of the Mn system. If the impurity concentration is below a certain threshold, the increase of the magnetization does not lead to a significant change in the localized character of the spin-polarized states. Above this threshold, we reach conditions allowing the occurrence of spin-polarized extended states at the Fermi level—more properly extended states in a very dirty metal—which are very sensitive to the average magnetization. The occurrence of a metal-to-non-metal transition has been surveyed around an optimum combination of the Mn concentration and the free carriers density. [ABSTRACT FROM AUTHOR]

GaAs layers doped by implantation of Mn and Mg ions to increase the hole concentration were synthesized and studied. Measurements using a SQUID magnetometer showed that there is ferromagnetism at temperatures as high as 400 K, which is related to the formation of the MnAs and Mn y Ga1 − y clusters as a result of high-temperature annealing, in addition to the formation of the Ga1 − x Mn x As alloy. The anomalous Hall effect was observed at temperatures in the range from 4.2 to 200 K. As temperature was increased starting with 4.2 K, the negative magnetoresistance with extremely large magnitude transformed into a giant positive magnetoresistance at T ≈ 35 K. [ABSTRACT FROM AUTHOR]

The effect of the growth temperature of an AlGaAs spacer on mobility μe of the 2D electron gas in pseudomorphic AlGaAs/InGaAs/GaAs structures with one-sided δ doping by silicon is studied The structures are optimized so that conduction over the doped layer is absent. In such structures, mobility μe increases by 53 and 69% at T = 300 and 77 K, respectively, as the growth temperature of the spacer rises from 590 to 610°C with other parameters and growth conditions fixed. Photoluminescence and X-ray diffraction analyses show that the mobility increases because the AlGaAs spacer crystal structure is improved and the AlGaAs/InGaAs interface becomes sharper. [ABSTRACT FROM AUTHOR]

The effect of growth temperature of the AlGaAs spacer layer on mobility in a two-dimensional electron gas μ e in single-side δ-doped pseudomorphic AlGaAs/InGaAs/GaAs transistor structures with a high electron mobility is studied experimentally. The energy-band diagram is analyzed using a self-consistent calculation. In order to study the electronic transport properties, an optimized structure in which there is no parallel conduction over the doped layer was chosen. It is shown that, in optimized structures, the mobility μ e increases by 53% at T = 300 K and by 69% at T = 77 K as the growth temperature increases from 590 to 610°C, with the other parameters and the growth conditions remaining the same. It is assumed that this behavior is related to an improvement in the structural quality of the AlGaAs spacer layer and the AlGaAs/InGaAs/GaAs heteroboundary. [ABSTRACT FROM AUTHOR]

Using the thermopower method (Seebeck effect), the semiconductor-metal transition that occurs in gallium arsenide single crystals of n and p types at ultrahigh pressures P above ∼11–18 GPa has been studied. It has been found that the transition in n-type samples begins at lower pressures. In the region of the semiconductor-metal phase transition, features have been observed on the thermopower dependences S( P). These features indicate that lattices intermediate between the initial semiconductor structure of zinc blende and the Cmcm high-pressure orthorhombic metallic phase are formed. By analogy with ZnTe, one intermediate phase (semiconductor with hole conductivity) is suggested to have the cinnabar structure and the second intermediate phase (semimetallic with electron conductivity) possibly has the SC16 structure. A model of the semiconductor-metal transition is discussed. The behavior of the thermoelectric properties in GaAs under pressure is compared with the behavior of these properties in other ANB8−N semiconductors, which also undergo the transition to the metallic state. [ABSTRACT FROM AUTHOR]

The energy and wave functions of localized electron states in a quantum well in a high magnetic field arbitrarily oriented with respect to the layers of the structure, and a high transverse electric field are studied. The situation where the quantum-confined energy and the Landau energy are close to each other is considered. The evolution of the spectrum with varying orientation of the magnetic field over the entire angle range is studied. [ABSTRACT FROM AUTHOR]

To find the parameters of low-barrier Schottky diodes, a diagnostics technique based on an analysis of the dependence of the differential resistance of a diode with a Mott barrier and near-surface δ-shaped doping is developed. It is shown that a complete description of the current-voltage characteristics of the diode is possible with regard to the series n −- n + junction. The technique makes it possible to optimize diodes to attain higher detection sensitivity. [ABSTRACT FROM AUTHOR]

We have studied the room-temperature photoconductivity in the wavelength range 1–2.6 μm in InAs/GaAs heterostructures with quantum dots (QDs). Specific features of these heterostructures grown using the metalorganic vapor phase epitaxy (MOVPE) were an increase in the amount of InAs during the formation of a sheet of QDs and the use of alternating low-and-high-temperature regimes during their overgrowth with a GaAs barrier layer. For the first time, the MOVPE-grown multilayer InAs/GaAs heterostructures with quantum dots exhibited photoluminescence in a wavelength range of up to 1.6 μm and the photoconductivity up to 2.6 μm at room temperature. The heterostructures exhibited a room-temperature voltage sensitivity of 3 × 103 V/W (within a Si-plate filter bandwidth) and a specific detectivity of 9 × 108 cm Hz1/2 W−1. [ABSTRACT FROM AUTHOR]

Zn-doped InP and GaInPAs layers were grown by OrganoMetallic Vapor-Phase Epitaxy (OMVPE). The epitaxial films consist of a primary GaInPAs/InP epitaxial layer and a secondary InP/GaInAs epitaxial layer. We present evidence that the redistribution of Zn acceptors in the primary epitaxial layer is strongly influenced by the Zn doping concentration in the secondary epitaxial layer. Rapid redistribution of Zn acceptors in the primary epitaxial layer occurs if the Zn doping concentration in the secondary epitaxial layer exceeds a critical concentration of N≅3×10cm. The influence of the growth temperature on this effect is also presented. [ABSTRACT FROM AUTHOR]

Optimized photoemitter of polarized electrons is based on the strained AlInGaAs/AlGaAs superlattice grown by the MBE method. Electron emission from the developed photocathode demonstrates maximal polarization of 92% with quantum efficiency of 0.85%. [ABSTRACT FROM AUTHOR]