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We investigate the polarization-induced doping in the gradient variation of Al composition in the p-Al0.75Ga0.25N/Al x Ga1− x N hole injection layer (HIL) for deep ultraviolet light-emitting diodes (DUV-LEDs) with an ultra-thin p-GaN (4 nm) ohmic contact layer capable of emitting 277 nm. The experimental results show that the external quantum efficiency (EQE) and wall plug efficiency (WPE) of the structure graded from 0.75 to 0.55 in the HIL reach 5.49% and 5.04%, which are improved significantly by 182% and 209%, respectively, compared with the structure graded from 0.75 to 0.45, exhibiting a tremendous improvement. Both theoretical speculations and simulation results support that the larger the difference between 0.75 and x in the HIL, the higher the hole concentration that should be induced; thus, the DUV-LED has a higher internal quantum efficiency (IQE). Meanwhile, as the value of x decreases, the absorption of the DUV light emitted from the active region by the HIL is enhanced, reducing the light extraction efficiency (LEE). The IQE and LEE together affect the EQE performance of DUV-LEDs. To trade off the contradiction between the enhanced IQE and decreased LEE caused by the decrease in Al composition, the Al composition in the HIL was optimized through theoretical calculations and experiments. [ABSTRACT FROM AUTHOR]

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 this paper we investigate interband cascade type-II mid-wavelength infrared InAs/GaSb superlattice detector in temperature range from 200 K to 300 K. The paper is based on the theoretical calculation of dark current treated as a sum of two components: average bulk current and average leakage current, flowing through the device. The average leakage current results from a comparison of theoretically calculated bulk current and measured one. We show that it is possible to fit theoretical model to experimental data, assuming that transport in absorber is determined by the dynamics of the intrinsic carriers. Based on the fit we estimated carrier lifetime greater than 100 ns in temperature range 200–300 K. [ABSTRACT FROM AUTHOR]

We report on the investigation of the surface leakage current for InAs1-xSbx (x=0.09) high operation temperature photodiode grown on GaAs substrate in accelerated short-term stability test. The electrochemical passivation technique was proposed to modify the mesa sidewalls properties and obtain anodic sulphur coating covered by SU-8 negative photoresist. The electrical behavior of sulphur anodic film, SU-8 photoresist, and unpassivated devices was compared for devices in variable area diode array test. The surface resistivity for anodic sulphur film, SU-8 and unpassivated devices are equal to 1080, 226, 10200 kO cm, respectively, at 150 K and 1340, 429, 2870 kO cm, respectively, at 150 K after an exposure of 20 h to atmosphere at 373 K. The Auger recombination process was evaluated as the main mechanism of diffusion current in HOT devices. [ABSTRACT FROM AUTHOR]

Diluted magnetic semiconductor (DMS) composed in magnetic tunnel junctions (MTJs) are predicted to have potential applications in spintronics. However, the crucial issue is how to control the magnetic order of DMSs. In our semiconductor MTJs (SMTJs) model, formed of ( Ga,Cr ) N/GaN/ ( Ga,Cr ) N multilayers, we found that the electrons can transfer from one (Ga,Cr)N electrode to another upon the external electric field, hence the magnetic interaction between two doped Cr ions in each (Ga,Cr)N DMS electrode can be changed from ferromagnetic to antiferromagnetic. The phenomenon proposes a possible way for the application of SMTJs. [ABSTRACT FROM AUTHOR]

Electrical and dielectric properties of Au/1% graphene (GP)+Ca1.9Pr0.1Co4O x doped poly(vinyl alcohol)/n-Si structures have been investigated using the admittance spectroscopy method in the temperature and voltage ranges of 160-300 K and -4 - 5 V, respectively. Experimental results show that both the main electrical and dielectric parameters, such as barrier height (Φb), depletion layer width ( Wd), series resistance ( Rs) of structure, real and imaginary parts of dielectric constant ( ε′, ε″) and electric modulus ( M′ and M″), tan δ, and AC conductivity ( σac) were found to be strong functions of temperature and applied bias voltage. M′ and M″ versus V plots have a peak at about 1 V. While the peak position shifted towards negative biases, the magnitude of the peak decreases with increasing temperature. Such peak behavior in M′ and M″ can be attributed to the existence of particular density distribution profile interface states at the interfacial layer-n-Si interface and their reordering and restructure under external electric field and interface polarization. These peaks also indicated that the Au/1% GP+Ca1.9Pr0.1Co4O x doped poly(vinyl alcohol)/n-Si structure exhibits relaxation phenomena. [ABSTRACT FROM AUTHOR]

Interlayer exchange coupling (IEC) in a series model diluted magnetic semiconductor (DMS) multilayer consisting of two magnetic (Ga, Mn)N layers separated by non-doped or Mg-doped GaN non-magnetic spacers has been studied by first-principles calculations. The effects of the spacer thickness and hole doping to the IEC were studied systematically. It is observed that, (1) for the GaN spacers without Mg doping, the IEC between two magnetic (Ga, Mn)N layers is always ferromagnetic, which is clarified as an intrinsic character of the Ruderman–Kittle–Kasuya–Yoshida (RKKY) interaction based on a two-band model for a gaped system; (2) for the Mg-doped GaN spacers, the IEC is tunable from ferromagnetic to antiferromagnetic by varying the spacer's thickness and the dopant's site. [ABSTRACT FROM AUTHOR]

Transparent and conducting cadmium oxide (CdO) and manganese doped CdO (Mn: CdO) thin films were deposited using a low cost spray pyrolysis method on the glass substrate at 300 °C. For Mn doping, various concentrations of manganese acetate (1–3 wt%) was used in the spraying precursor solution. The structural, electrical and optical properties of CdO and Mn: CdO films were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), UV–vis and Hall measurement. X-ray diffraction study reveals that the CdO and Mn: CdO films are possessing cubic crystal structures. SEM and AFM studies reveal that the grain size and roughness of the films are increased with increasing Mn doping concentration. Optical transmittance spectra of the CdO film decreases with increasing doping concentration of manganese. The optical band gap of the films decreases from 2.42 eV to 2.08 eV with increasing concentration of manganese. A minimum resistivity of 1.11×10 −3 Ω cm and maximum mobility of 20.77 cm 2 V −1 s −1 is achieved for 1 wt% of manganese doping. [ABSTRACT FROM AUTHOR]

We deposited amorphous indium gallium nitride (a-In xGa1- xN) films at room temperature by reactive radio frequency sputtering with GaN and InN targets and investigated the change of their properties from thermal annealing at annealing temperatures, Ta, below 200 °C. A large change in the indium and nitrogen composition ratios was not observed by thermal annealing at a Ta below 200 °C. In the X-ray diffraction patterns of the films annealed at a Ta below 200 °C, no perceivable peaks assigned to crystalline In xGa1- xN were found. The photoconductivty, σp, increased with an increase in Ta. On the other hand, the increase of the dark conductivity, σd, was very small with an increase in Ta below 200 °C. As a result, the photosensitivity, σp/ σd, increased from 252 to 2500 by thermal annealing at a Ta of 200 °C. [ABSTRACT FROM AUTHOR]

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Highlights: [•] SiC MOSFETs and GaN HEMTs are excellent candidates for next generation of energy efficient power electronics. However, several physical and technological issues related to the passivation of surfaces and interfaces still affect the performance of these devices (limiting the energy efficiency). [•] Nitrogen- and Phosphorous-based passivation processes for SiO2/SiC interfaces are able to decrease the interface state density and to increase the 4H-SiC MOSFET mobility. [•] N and P not only passivate the interface state density D it but also increases the conductivity of SiC channel region by “counter doping” effect. [•] While significantly higher mobility is achieved after annealing in POCl3, large P-incorporation leads to undesired threshold voltage instability. [•] Surface passivation and gate insulation are mandatory to increase the efficiency of HEMTs. [•] Besides widely used PECVD SiN, “in situ” SiN seems to be a good candidate for surface passivation. Moreover, also high-k dielectrics (HfO2, CeO2, …) are emerging since they can reduce the leakage current and current collapse effects, without penalizing the transconductance (g m) and the threshold voltage (V th). [•] Novel cost effective processes, like selective thermal oxidation of AlGaN surfaces, are also under investigation for passivating surface defects (V-defects) and reducing the leakage current. [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]

Abstract: We present calculations of carrier confinement characteristics in (Al y Ga1−y N/AlN)SLs/GaN/(In x Ga1−x N/GaN)MQW/GaN heterojunction structure in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrödinger, Poisson, potential and charge balance equations. An optimization of In x Ga1−x N/GaN multiquantum-well (MQW) was made firstly including thickness of GaN channel, InGaN, and indium composition of In x Ga1−x N in order to increase carrier density and mobility, and the influence of pairs of AlGaN/AlN superlattices (SLs) and InGaN/GaN MQWs on structure was discussed. Theoretical calculations clearly indicate that the two-dimensional electron gas (2DEG) sheet carrier density in designed heterostructure is greatly increased due to the enhancing of carrier confinement compared to those in conventional AlGaN/GaN one at the similar Al composition. Furthermore, the calculated carrier distribution shows that carrier mobility will be improved by reducing interface roughness and alloy disorder scattering in designed heterostructure. [Copyright &y& Elsevier]

Abstract: In this article, the significant effect of a thin gate thermal oxide layer on InGaP/InGaAs doping-channel field-effect transistors (DCFETs) is first demonstrated. When compared to the conventional InGaP/InGaAs DCFET, the device with the gate thermal oxide layer exhibits a higher gate turn-on voltage and nearly voltage-independent transconductances as the gate-to-source is biased form −0.75V to 0V, while the maximum transconductance is lower. Experimentally, the transconductance within 90% of its maximum value for gate voltage swing is 1.63V in the gate-oxide device, which is greater than that of 1.35V in the device without the gate thermal oxide layer. Furthermore, it maintains a high drain current level at negative gate bias in the gate-oxide device, which can be attributed that the thermal oxide layer with a considerably large energy gap absorbs more of gate negative voltage and the influence of negative voltage on the gate depleted thickness is relatively slight. [Copyright &y& Elsevier]

Abstract: The performance of GaN based devices could possibly be improved by utilizing the good p-type properties of GaP layer and it provides the possibility of the integration of InAlGaN and AlGaInP materials to produce new devices, if high quality GaP compounds can be grown on III-nitride compounds. In this paper, the growth of GaP layers on GaN by metalorganic chemical vapor deposition (MOCVD) has been investigated. The results show that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature GaP growth. Using a 40nm thick GaP buffer layer, a single crystal GaP layer, whose full-width at half-maximum of the (111) plane measured by double crystal X-ray diffraction is 580″, can be grown on GaN. The V/III ratio plays an important role in the GaP layer growth and an appropriate V/III ratio can improve the quality of GaP layer. The GaP:Mg layer with hole carrier concentration of 4.2×1018 cm−3 has been obtained. [Copyright &y& Elsevier]

Abstract: Ni thin layer was deposited to assist to activate p-GaN and then was removed. The process was named Ni-assisted annealing (NA). We investigate the surface morphology and p-type contact behaviors of InGaN LED films grown on Si (111) substrates. Compared with conventional thermal annealing (TA), NA can improve the p-type contact characteristic at lower anneal temperature and a smaller specific contact resistivity (ρ c =6.1×10−5 Ωcm2) employing nonalloy Pt electrode was obtained. A wet etching method using acid–hydrogen peroxide was adopted to boil films surface after activation. We found that some nano-pits appeared on surfaces while original surface step structure was still clearly visible, which shows a defect-selective etching characteristic. Otherwise, we demonstrated that the surface morphology could be affected by NA while independent to TA. Some mechanisms for experimental phenomena were also discussed in the letter. [Copyright &y& Elsevier]

Abstract: This work is concerned with the theoretical study of the combined effects of applied electric field and hydrostatic pressure on the binding energy and impurity polarizability of a donor impurity in laterally coupled double InAs/GaAs quantum-well wires. calculations have been made in the effective mass and parabolic band approximations and using a variational method. The results are reported for different configurations of wire and barriers widths, impurity position, and electric field and hydrostatic pressure strengths. Our results show that for symmetrical structures the binding energy is an even function of the impurity position along the growth direction of the structure. Also, we found that for hydrostatic pressure strength up to 38kbar, the binding energy increases linearly with hydrostatic pressure, while for larger values of hydrostatic pressure the binding energy has a nonlinear behavior. Finally, we found that the hydrostatic pressure can increase the coupling between the two parallel quantum well wires. [Copyright &y& Elsevier]

Abstract: Wide band gap (WGB) materials are the most promising semiconductors for future electronic devices, and are candidates to replace the conventional materials (Si, GaAs, …) that are approaching their physical limits. Among WBG materials, silicon carbide (SiC) and gallium nitride (GaN) have achieved the largest advancements with respect to their material quality and device processing. Clearly, the devices performances depend on several surface and interface properties, which in turn are often crucially determined by the quality of the available material, as well as by the device processing maturity. In this paper, some surface and interface issues related to SiC and GaN devices processing are reviewed. First, the control of metal/SiC barrier uniformity and surface preparation will be discussed with respect to the performance of Schottky-based devices. Moreover, the impact of high-temperature annealing required for high-voltage Schottky diodes and MOSFETs fabrication, on the surface morphology and device performances will also be briefly presented. In the second part, it will be shown that for GaN the material quality is still the main concern, since dislocations have a severe influence on the current transport and barrier homogeneity of metal/GaN interfaces. Other practical implications of thermal annealing and surface passivation during GaN-based devices fabrication will also be addressed. [Copyright &y& Elsevier]

Abstract: This paper attempts to realize unpinned high-k insulator–semiconductor interfaces on air-exposed GaAs and In0.53Ga0.47As by using the Si interface control layer (Si ICL). Al2O3 was deposited by ex situ atomic layer deposition (ALD) as the high-k insulator. By applying an optimal chemical treatment using HF acid combined with subsequent thermal cleaning below 500°C in UHV, interface bonding configurations similar to those by in situ UHV process were achieved both for GaAs and InGaAs after MBE growth of the Si ICL with no trace of residual native oxide components. As compared with the MIS structures without Si ICL, insertion of Si ICL improved the electrical interface quality, a great deal both for GaAs and InGaAs, reducing frequency dispersion of capacitance, hysteresis effects and interface state density (D it). A minimum value of D it of 2×1011 eV−1 cm−2 was achieved both for GaAs and InGaAs. However, the range of bias-induced surface potential excursion within the band gap was different, making formation of electron layer by surface inversion possible in InGaAs, but not possible in GaAs. The difference was explained by the disorder induced gap state (DIGS) model. [Copyright &y& Elsevier]

Abstract: The 32 possible kinds of B3C10N3 monolayer were built following the constraints derived from previous experiments. Conducting and semiconducting monolayer were found after geometry optimization by local density approximation (LDA) in CASTEP. By stacking monolayer with relatively lower energies in AB sequence, different B3C10N3 layer structures were built. According to the calculation results, structural and electronic properties for two typical structures, conducting and semiconducting B3C10N3 were investigated. [Copyright &y& Elsevier]

Abstract: Recent experimental investigations revealed that the biaxial stress in thin InGaN layers grown on thick GaN layer induces a large piezoelectric field along [0001] orientation that causes red-shift in optical transitions and reduction in oscillator strengths because of spatial separation of the electron and hole wave functions. In this Letter based on theoretical modeling we determined the well width z-dependent effect on red-shifted quantum-confined Stark effect (QCSE) in GaN/In x Ga1− x N () strained quantum well structures. Analyses are based on the solution of Schrödinger equation in a finite well including the internal piezoelectric electric field (F) due to the strained polarization as the perturbation potential. Our theoretical results show: (1) the red-shift in optical transition has a quadratic well-width form as it is for infinite wells (Davies, 1998) , (2) assuming the model based on a carrier effective mass dependence on the width of quantum wells, , fits the experimental data (Takeuchi et al., 1997) much more accurate compare to the model with constant effective mass, . [Copyright &y& Elsevier]

Abstract: The transport properties of Mg doped and undoped InN films are studied with capacitance-voltage, thermopower, and Hall mobility measurements. A positive Seebeck coefficient is observed for Mg doped InN confirming p-type conductivity, though high doping and structural defect density can lead to n-type films. Transport measurements of undoped films are analyzed employing Rode''s iterative Boltzmann equation method. Observed thermopower, Hall mobility, and dislocation density data for undoped films are consistent with calculations including the effects of charged line defect (donor-type dislocation) scattering. [Copyright &y& Elsevier]

Abstract: Heterostructures consisting of an InGaSb quantum well situated between AlGaSb barriers were grown by molecular beam epitaxy. Calculations indicate a type-I band structure with substantial valence and conduction band offsets that can allow for the confinement of either electrons or holes in the InGaSb. Quantum wells with n-type conduction were achieved using modulation doping, with Te located in the barrier above the quantum well. A set of barrier layers was found which resulted in a sample with an In0.2Ga0.8Sb quantum well that exhibited an electron mobility of 3900cm2/Vs as grown. After removal of upper barrier layers including the Te by selective etching, the conductivity switched to p-type, with hole mobilities near 800cm2/Vs. This design could allow the integration of low-power n- and p-channel field-effect transistors for complementary logic applications. [Copyright &y& Elsevier]

Abstract: A high-quality ferromagnetic GaMnN (Mn=2.8at%) film was deposited onto a GaN buffer/Al2O3(0001) at 885°C using the metal-organic chemical vapor deposition (MOCVD) process. The GaMnN film shows a highly c-axis-oriented hexagonal wurtzite structure, implying that Mn doping into GaN does not influence the crystallinity of the film. No Mn-related secondary phases were found in the GaMnN film by means of a high-flux X-ray diffraction analysis. The composition profiles of Ga, Mn, and N maintain nearly constant levels in depth profiles of the GaMnN film. The binding energy peak of the Mn 2p3/2 orbital was observed at 642.3eV corresponding to the Mn (III) oxidation state of MnN. The presence of metallic Mn clusters (binding energy: 640.9eV) in the GaMnN film was excluded. A broad yellow emission around 2.2eV as well as a relatively weak near-band-edge emission at 3.39eV was observed in a Mn-doped GaN film, while the undoped GaN film only shows a near-band-edge emission at 3.37eV. The Mn-doped GaN film showed n-type semiconducting characteristics; the electron carrier concentration was 1.2×1021/cm3 and the resistivity was 3.9×10−3 Ωcm. Ferromagnetic hysteresis loops were observed at 300K with a magnetic field parallel and perpendicular to the ab plane. The zero-field-cooled and field-cooled curves at temperatures ranging from 10 to 350K strongly indicate that the GaMnN film is ferromagnetic at least up to 350K. A coercive field of 250Oe and effective magnetic moment of 0.0003μB/Mn were obtained. The n-type semiconducting behavior plays a role in inducing ferromagnetism in the GaMnN film, and the observed ferromagnetism is appropriately explained by a double exchange mechanism. [Copyright &y& Elsevier]

Abstract: We have studied the magnetic field effects on the diamagnetic susceptibility and binding energy of a hydrogenic impurity in a quantum well-wire by taking into account spatially dependent screening. Using the effective-mass approximation within a variational scheme, binding energy and diamagnetic susceptibility of donor are obtained as a function of the magnetic field, length of the square quantum well-wire for different impurity positions. It is shown that the magnetic field effects on diamagnetic susceptibility can be more important for donors in quantum well-wires over a large range of wire dimensions. [Copyright &y& Elsevier]

Abstract: The defect evolution and its correlation with electrical properties of GaN films grown by metalorganic chemical vapor deposition are investigated. It is found that the dislocation density decreases gradually during the growth process, and the dislocation reduction rate in the island coalescence process is especially rapid. The changes in electron mobility of GaN with the increase of growth time are mainly dependent on the dislocations acting as scattering centers. Furthermore, the variation of carrier concentration in GaN may be related with the point defects and their clusters. The quality of GaN could be improved by suitably increasing the film thickness. [Copyright &y& Elsevier]

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]

Abstract: A systematic study of the crystallographic and electrical/optical properties of MOVPE-grown InN was performed, and the factors that restrict the quality of MOVPE InN were elucidated. The quality of grown InN is highly dependant on the thermal decomposition of NH3 as a nitrogen source. At a lower growth temperature (~550°C) a shortage of active nitrogen, due to a lower decomposition rate of NH3, causes the formation of N vacancies in the grown InN. With increasing growth temperature, a more stoichiometric crystal is grown and the electrical/optical properties improve. At temperatures above 600°C, however, deterioration occurs at the N-face of In-polar InN near the substrate interface. This deterioration results in the formation of a porous layer during high temperature (~650°C) growth. There are a few evidences that show that the hydrogen produced by NH3 decomposition causes this degradation. Thus, improving the quality of MOVPE-grown InN by changing the growth temperature can be difficult. However, a short growth time at a high growth rate and a relatively high temperature is one effective way to solve this dilemma, and one can achieve carrier concentrations as low as 4×1018 cm−3 by growth at 650°C for 30min. [Copyright &y& Elsevier]

Abstract: Thin InAs epilayers were grown on GaAs(100) substrates exactly oriented and misoriented toward [111]A direction by atmospheric pressure metalorganic vapor phase epitaxy. InAs growth was monitored by in situ spectral reflectivity. Structural quality of InAs layers were studied by using high-resolution X-ray diffraction. No crystallographic tilting of the layers with respect to any kind of these substrates was found for all thicknesses. This result is discussed in terms of In-rich growth environment. InAs layers grown on 2° misoriented substrate provide an improved crystalline quality. Surface roughness of InAs layers depend on layer thickness and substrate misorientation. [Copyright &y& Elsevier]

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]

Abstract: The low-pressure MOVPE-grown p-InGaAs-on-n-InP and n-InP-on-p-InGaAs diodes were characterized by I–V and C–V measurements to study the effects of the growth conditions on the heterointerface. The obtained band discontinuity in the conduction band ΔEc ranged from 0.19 to 0.32eV. It was found that ΔEc was very sensitive to the growth interruption at the InP/InGaAs heterointerface. The n-InP-on-p-InGaAs diodes tend to show higher ΔEc than the p-InGaAs-on-n-InP diodes. The decreased ΔEc at InGaAs-on-InP heterointerface might be attributed to the graded layer of InGaAsP formed by intermixing at the interface. It is concluded from the estimated ΔEc that the InP-on-InGaAs heterointerface is more abrupt than the InGaAs-on-InP heterointerface. An improvement of the InGaAs-on-InP heterointerface is mandatory for fabrication of high-performance double heterojunction bipolar transistors with InP collector layers. [Copyright &y& Elsevier]

Abstract: We developed a technology of sub-micrometer Hall probes for future application in scanning hall probe microscopy (SHPM) and magnetic force microscopy (MFM). First, the Hall probes of ∼9-μm dimensions are prepared on the top of high-aspect-ratio GaAs pyramids with an InGaP/AlGaAs/GaAs active layer using wet-chemical etching and non-planar lithography. Then we show that the active area of planar Hall probes can be downsized to sub-micrometer dimensions by local anodic oxidation technique using an atomic force microscope. Such planar probes are tested and their noise and magnetic field sensitivity are evaluated. Finally, the two technologies are combined to fabricate sub-micrometer Hall probes on the top of high-aspect ratio mesa for future SHPM and MFM techniques. [Copyright &y& Elsevier]

Abstract: Cubic boron nitride (cBN) thick films deposited on mainly c-axis-oriented graphite substrate at room temperature and zero bias by radio frequency (RF) magnetron sputtering were studied. In the growth process, RF power plays a key role in determining the content of cubic phase in films, while the conventional substrate heating and biasing have been neglected. With increase in RF power, the dominated content of films converts from explosion boron nitride (eBN) to cBN. The transformation mechanism has been discussed. The unique structural properties of the “soft” graphite are favorable to propose simple conditions for growing “hard” cBN films. Furthermore, the optical band gap of BN films having ∼90% cubic phase is of ∼5.8eV obtained from ultraviolet–visible optical transmission measurement. The electron field emission examination shows that cBN film on graphite has a high emission current density of 2.8×10−5 A/cm2 at an applied field of ∼30V/μm. [Copyright &y& Elsevier]

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]

Abstract: Titania and composite (Ag, Au, W) titania coatings were prepared on glass microscope slides via a sol–gel dip-coating method. The resulting coatings were characterised by X-ray diffraction, Raman, scanning electron microscopy (SEM), wavelength dispersive X-ray (WDX), Brunauer–Emmett–Teller (BET) surface area analysis, atomic force microscopy (AFM) and UV–visible absorption techniques. Photocatalytic activity of the coatings was determined by photomineralisation of stearic acid under 254, 365nm and white light sources monitored by FT-IR spectroscopy. These activities at 254 and 365nm light were represented as formal quantum efficiencies (FQEs) after determination of photon flux. Water contact angle measurements were made before and after irradiation with monochromatic 254 or 365nm light; all films demonstrated photo-assisted super hydrophilicity (PSH). A Ag:Au titania composite coating was found to be the most significant photoactive film. The mode of improved photocatalytic activity was postulated in terms of a charge separation model. The Ag:Au TiO2 coating showed potential as a useful coating for hard self-cleaning surfaces due to its robustness, stability to cleaning and reuse and its photoactive response to indoor lighting conditions. [Copyright &y& Elsevier]

Abstract: Synthetic single-crystalline samples of Fe3O4 magnetite were subjected to fast neutron bombardment with a fluency Φ=2.2×1020 cm−2. A comparative study of the electrical resistivity ρ, normal (ordinary) and anomalous (extraordinary) Hall effects, and the magnetoresistance in a temperature range from 50 to 400 K (i.e across the Verwey transition (VT) at 125 K) was performed on both as grown and irradiated samples. The galvanomagnetic properties were investigated in magnetic fields up to 13.6 T. From the normal (ordinary) Hall effect the concentration of charge carriers was determined. The activation energy was also estimated. On the Verwey transition the conductivity type was changed form electronic to hole. Contrary to expectations, the fast neutron irradiation resulted only in a minor decrease in by ∼4 K. The results gathered evidence against a distributed opinion that the charge ordering on the octahedral sites in the spinel structure of Fe3O4 is a major driving factor of the Verwey transition. [Copyright &y& Elsevier]

Abstract: Using an AlInN intermediate layer, GaN was grown on (111)Si substrate by selective metalorganic vapor phase epitaxy. The variation of the surface morphology was investigated as a function of the In composition and thickness of the AlInN layer. It was found that the In composition in the AlInN layer was a function of the growth temperature and thickness. Because of the small band offset at the AlInN/Si hetero-interface, we have achieved a low series resistance of the order of 9Ω (0.0036Ωcm2) across the GaN/AlInN/AlN/Si layer structure. [Copyright &y& Elsevier]

Abstract: Adopting anisotropy etching method, a (111) facet of Si is obtained on a Si substrate and selective area growth (SAG) of GaN is performed with metal-organic vapor phase epitaxy on the facet. The epitaxial lateral overgrowth of (11¯01), (112¯2) GaN is investigated on (001) and (113) Si substrate, respectively, and the incorporation properties of Si, C, and Mg elements are discussed in relation to the atomic configuration on the surface. Analyzing the optical and electrical properties of C-doped (11¯01) GaN layer, it is shown that carbon creates a shallow acceptor level. On the thus prepared (11¯01) GaN layer, a light emitting diode (LED) with a C-doped p-type layer is fabricated. [Copyright &y& Elsevier]

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]

Abstract: C60 uniformly doped and δ-doped GaAs layers are grown by migration enhanced epitaxy method. Crystalline and electrical characteristics of the layers are investigated by reflection high energy electron diffraction, X-ray diffraction and capacitance–voltage (C–V) measurements. C60 high-concentration doping is found to introduce 2D defects, and X-ray diffraction pole-figure measurements show that the rotational domains appear predominantly on {111}A plane. This indicates that C60 molecules are mainly incorporated on the dangling bonds of Ga atoms due to the high binding energy between C60 molecules and Ga atoms. C60 uniformly doped GaAs layers show highly resistive characteristics, suggesting that C60 molecules cannot be decomposed into isolated C atoms in the GaAs lattice, and they behave as if they were electron traps or strong recombination centers. C–V profiles of Cr–Au/C60 δ-doped GaAs Schottky diode suggest that C60 molecules in GaAs lattice produce electron traps which can be charged or discharged by applied electrical field. [Copyright &y& Elsevier]

Abstract: MBE-grown single-crystal Gd2O3 epitaxially on GaN has exhibited excellent thermal stability, withstanding rapid thermal annealing (RTA) at 1100°C. The high-κ dielectric Gd2O3 thin film 10nm thick has a monoclinic phase with a high degree of crystallinity, characterized by X-ray diffraction using synchrotron radiation. The orientation relationship is and . Interface between Gd2O3 and GaN remains atomically sharp after the RTA, as demonstrated using X-ray reflectivity and high-resolution transmission electron microscopy. Gd2O3/GaN metal-oxide-semiconductor capacitors show well-behaved capacitance–voltage characteristics with small dispersion and hysterisis, a high dielectric constant of ∼17, and a low electrical leakage current density of 4.6×10−9 A/cm2 at 1MV/cm. [Copyright &y& Elsevier]

Abstract: In this work we study both the structural and electrical qualities of AlGaN/GaN high electron mobility transistor heterostructures grown on silicon(111) by molecular beam epitaxy. Correlations are established between the quality of the structures and the relaxation rate of the mismatch stress in layers grown using ammonia as a nitrogen source. Comparison with layers grown using a nitrogen plasma source confirms the primordial role of the growth temperature for stress relaxation and dislocation filtering. [Copyright &y& Elsevier]

Abstract: We describe the molecular-beam epitaxial (MBE) growth and fabrication of III–V metal-oxide-semiconductor (MOS) devices on Ge/Si virtual substrates. We show that high-temperature in-situ H2 annealing in the chemical-vapor deposition system changes the Ge surface configuration and produces a surface with predominantly double-step-layer conditions, which is crucial for the growth of single-domain GaAs. In addition, the surface morphology of III–V on Ge/Si improved significantly with an annealing treatment of the Ge surface carried out under high arsenic background pressure in the MBE chamber. This facilitates uniform As-monolayer formation on the entire Ge surface. Low-temperature migration-enhanced epitaxy (MEE) and low-temperature conventional GaAs growth not only enhance the growth of single-domain GaAs without Ge outdiffusion but also produce a sufficiently smooth surface for high-k dielectric deposition, achieving low leakage current. A 300-nm-thick GaAs buffer layer was grown, followed by a 10nm growth of In0.2Ga0.8As high-mobility channel layer. A 7–8-nm-thick Al2O3 layer was deposited ex-situ by atomic-layer deposition (ALD). We verify the quality of III–V growth using transmission electron microscopy (TEM), X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and photoluminescence (PL) measurement. The C–V characteristics show unpinning of the Fermi level, which is a necessary condition for gate voltage control of the drain current. This work suggests this materials combination is a promising candidate for the realization of advanced, nonclassical complementary-MOS and optoelectronic devices on Si substrates. [Copyright &y& Elsevier]

Abstract: Depletion-mode In0.2Ga0.8As/GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated with molecular beam epitaxy (MBE) grown Al2O3/Ga2O3(Gd2O3) as the gate dielectric in two comparable processes. In the “metal-gate-last” process, a 12μm gate-length depletion-mode n-channel InGaAs/GaAs MOSFET with a Ga2O3(Gd2O3) gate oxide 6nm thick shows an accumulated drain current density of 135mA/mm at V g=2V. In the other process of “metal-gate-first” process, the device with same gate dielectric, channel, and gate length exhibits a larger drain current density of 175mA/mm at the same gate bias. In addition, there is a broader transfer characteristics and higher extrinsic peak transconductance of 48mS/mm in the metal-gate-first process. MOS capacitors from both processes have exhibited excellent capacitance–voltage (C–V) characteristics with minor dispersion, negligible hysteresis, and κ values of 13.7–13.9 in Ga2O3(Gd2O3). [Copyright &y& Elsevier]