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We study the effect of the addition of p- or n-type doping gases, trimethylboron (TMB) or phosphine, respectively, on cluster formation in the SiH4/H2 plasma used for the deposition of hydrogenated polymorphous silicon thin films. The formation of clusters is monitored using time-resolved measurements of the second harmonic of the radio frequency current J2. We show that the addition of PH3 does not change the cluster formation, while the addition of a small amount of trimethylboron strongly affects its charging behavior, preventing to some extent its agglomeration. The most ordered pm-Si:H thin films are obtained under conditions from which not only clusters but also larger silicon agglomerates are formed in the plasma and contribute to the deposition. The inhibiting role of TMB on the agglomeration and powder formation is evidenced by the smoothness of p-type films at high rates, as deduced from the sample surface topography obtained by atomic force microscopy measurements. [ABSTRACT FROM AUTHOR]

We report remarkably the enhanced thermoelectric performance of Sn-Zn co-doped In2O3 that were synthesized by a solid-state reaction followed by spark plasma sintering in the mid-temperature range. The X-ray diffraction study indicates that Sn and Zn were successfully co-substituted at the In site without forming any additional phase even at 8% doping concentration. The co-substitution shows a significant increase in the electrical conductivity by band structure modification resulting in a significantly enhanced power factor. The point defect engineering combined with nanostructuring using a high energy ball milling suppressed the lattice thermal conductivity, which eventually resulted in an increased ZT value of 0.32 at 973 K, that is, about 7 times higher than that of pure In2O3. Thus, this study demonstrates the important role of co-substitution in improving the thermoelectric properties of n-type oxides. [ABSTRACT FROM AUTHOR]

Hydrogen-doped indium oxide (IO:H) has recently garnered attention as a high-performance transparent conducting oxide (TCO) and has been incorporated into a wide array of photovoltaic devices due to its high electron mobility (>100 cm2/V s) and transparency (>90% in the visible range). Here, we demonstrate IO:H thin-films deposited by sputtering with mobilities in the wide range of 10–100 cm2/V s and carrier densities of 4 × 1018 cm–3–4.5 × 1020 cm–3 with a large range of hydrogen incorporation. We use the temperature-dependent Hall mobility from 5 to 300 K to determine the limiting electron scattering mechanisms for each film and identify the temperature ranges over which these remain significant. We find that at high hydrogen concentrations, the grain size is reduced, causing the onset of grain boundary scattering. At lower hydrogen concentrations, a combination of ionized impurity and polar optical phonon scattering limits mobility. We find that the influence of ionized impurity scattering is reduced with the increasing hydrogen content, allowing a maximization of mobility >100 cm2/V s at moderate hydrogen incorporation amounts prior to the onset of grain boundary scattering. By investigating the parameter space of the hydrogen content, temperature, and grain size, we define the three distinct regions in which the grain boundary, ionized impurity, and polar optical phonon scattering operate in this high mobility TCO. [ABSTRACT FROM AUTHOR]

The influence of Fe doping for Mn in CoMn1-xFexGe alloys on their structural and magnetic phase transitions was investigated. CoMn1-xFexGe alloys display a first-order magneto-structural transition from a high temperature paramagnetic hexagonal Ni2In-type crystal structure to a low temperature ferromagnetic orthorhombic TiNiSi-type structure. An entropy change of ΔSM=-32.8 J/kgK was measured and adiabatic temperature change of -8.0K was computed for the x=0.085 alloy under a magnetic field of 7 T in the vicinity of the phase transition at 317 K. With increasing Fe content, transition temperatures and magnetic entropy changes decrease. In addition to investigating the effect of replacing Mn with Fe, the accessibility of the giant measured entropy change was quantified by means of the minimum magnetic field required to start and to complete the magnetostructural phase transition. [ABSTRACT FROM AUTHOR]

Superlattice-like (SLL) SnSb4/Ga3Sb7 (SS/GS) thin films were investigated through in-situ film resistance measurement. The optical band gap was derived from the transmittance spectra by using a UV-visible-NIR (ultraviolet-visible-near infrared) spectrophotometer. Transmission electron microscopy was used to observe the micro-structure before and after annealing. Phase change memory cells based on the SLL [SS(3 nm)/GS(4.5 nm)]7 thin films were fabricated to test and verify the operation consumption and switching endurance. The scanning thermal microscopy was used to probe the nanoscale thermal property. [ABSTRACT FROM AUTHOR]

Elastically strained supermultiperiod (100–1000 periods) AlGaAs/GaAs superlattices with different doping levels and slightly differing period thicknesses have been investigated. The proposed technique of characterization consisting of combined application of deep X-ray reflectometry based on a rigorous calculation method, as well as the well-known method of high-resolution X-ray reflectometry, has made it possible to investigate 100-period structures with 2-nm-wide Al0.3Ga0.7As barriers and 10-nm-wide GaAs wells and determine with a high accuracy the layer thicknesses and spread of interfaces. This achievement can be considered as a first step in further analysis of thick structures using bright synchrotron radiation source. The difference between the expected and obtained by the proposed method layer thicknesses is several percent, including that for samples with a high doping level (up to 1018 cm–3). All supermultiperiod structures are characterized by sharp interfaces with a standard deviation of about 0.1 nm. Based on the obtained data on the thicknesses, one can accurately determine the layer compositions using high-resolution X-ray diffraction. [ABSTRACT FROM AUTHOR]

PbTiO3/BaTiO3 ferroelectric superlattices commensurately constrained by a SrTiO3 substrate are studied using both phenomenological theory and phase field simulations. It is found that the spontaneous polarization of the superlattice does not vary significantly with volume fraction until PbTiO3 becomes the majority of the superlattice. A minimum tetragonality exists at room temperature when the PbTiO3 volume fraction is around 90%, resulted from its different sensitivity to epitaxial strains and the electrostatic coupling of the two polarized layers in this PbTiO3/BaTiO3 superlattice. [ABSTRACT FROM AUTHOR]

In this study, the metal-organic chemical vapor deposition growth and electrical properties of N-polar modulation doped p-AlGaN/GaN superlattices (SLs) were investigated. Hole sheet charge density and mobility were studied as a function of the concentration of the p-type dopant Mg in the SL and the number of SL periods. Room temperature Hall measurements were carried out to determine the hole mobility and the sheet charge density. While the hole density increased with the increasing number of SL periods, the hole mobility was largely unaffected. Hole mobilities as high as 18 cm2/V s at a simultaneously high hole density of 6.5 × 1013 cm−2 were observed for N-polar SLs with a Mg modulation doping of 7.5 × 1018 cm−3. For comparable uniformly doped Ga-polar SL samples, a mobility of 11 cm2/V s was measured. These results confirm the presence of abrupt Mg doping profiles in N-polar p-type GaN/AlxGa(1−x)N SL, allowing the demonstration of SLs with properties comparable to those of state-of-the-art Ga-polar modulation doped AlGaN/GaN SLs grown using molecular beam epitaxy. The lowest sheet resistance in the GaN/AlGaN material system of 5 kΩ/◻ is also reported. Test-structure transistors were also fabricated to investigate the applicability of these SL structures, with the planar device resulting in a current of 5 mA/mm and a FinFET structure resulting in a current of over 100 mA/mm. [ABSTRACT FROM AUTHOR]

A comparison of the features of electron transport in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a similar design is performed. However, the number of periods and diode areas are different. The values of the parasitic resistances of the near-contact diode regions are correlated, and the specific voltage drop across one superlattice period is determined for all special points in the current–voltage characteristics of the diodes. The mechanism of the appearance of stable current oscillations in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a high doping level is investigated. [ABSTRACT FROM AUTHOR]

Disklike molecules were introduced as chiral dopants to induce a pitch gradient in the polymer stabilized cholesteric liquid crystals films. A sandwich-cell was fabricated with two different substrates, one of which was coated by the disklike molecule layer and another by a parallel-aligned pattern of polyvinyl alcohol. The pitch gradient was formed by molecular diffusion across the film thickness and further stabilized by photo-initiated crosslinking of the polymerizable monomers during the diffusion process. The effect of the deposition amount of the disklike chiral molecules on the diffusion rate and the consequent pitch gradient was studied. [ABSTRACT FROM AUTHOR]

We report on the transport properties of electron-doped manganite Ca1-xCexMnO3 (CCMO, 0≤x≤0.08) films and superlattices composed of insulating layers CaMnO3 (CMO) and Ca0.92Ce0.08MnO3 (CCMO8), deposited on nearly lattice-matched NdAlO3 substrates. The CCMO (x=0.06 and 0.07) films show colossal magnetoresistance (CMR) accompanied with magnetorelaxor behavior, which can be ascribed to the phase separation of canted G-type antiferromagnetic metal and C-type antiferromagnetic insulator. The (CMO)m/(CCMO8)n superlattices with 4≤m, n≤8 (unit cells) resemble the solid-solution CCMO (x=0.06 and 0.07) films in CMR and magnetorelaxor behavior, suggesting that the phase separation takes place in the superlattices. The CMR and magnetorelaxor behavior of the (CMO)m/(CCMO8)n superlattices strongly depend on the thicknesses of constituent CMO and CCMO8 layers. The origin of the phase separation in the superlattices is discussed in terms of the charge transfer and the phase competition at the interfaces. [ABSTRACT FROM AUTHOR]

In this work we study the influence of manganese doping on the electromechanical properties of PZN–12%PT single crystal. The full electromechanical tensor of doped PZN–12%PT in the tetragonal single domain state is determined by the resonance-antiresonance method. Doping leads to a decrease in the dielectric transverse permittivity [variant_greek_epsilon]11T and of the shear piezoelectric coefficient d15. We show by dielectric constant [variant_greek_epsilon]33T measurements that the single domain state in doped crystal is stable in plates as thin as 90 μm, whereas it was unstable in plates thinner than 300 μm for the undoped crystals. This intrinsic effect is discussed by using a volume effect model based on the symmetry conforming principle of point defects. [Ren, Nature Mater. 3, 91 (2004)]. Mn doping forces the stability of PZN–12%PT single domain state, which makes the doped crystal a most suitable candidate than the pure crystal for high frequency ultrasonic medical imaging probe. [ABSTRACT FROM AUTHOR]

A systematic study on the energy level alignment, chemical interaction, and electron doping at interfaces between bathocuproine (BCP) and various types of metals (Au, Cu, Ag, Mg, and Ca) was carried out by performing ultraviolet photoelectron spectroscopy and electronic conductivity measurements. The energy level alignment at BCP/metal interfaces was found to depend on the metal work function ([uppercase_phi_synonym]m). For BCP on Au and Cu, whose [uppercase_phi_synonym]m exceeds 4.3 eV, the energy shift in the highest occupied molecular orbital (HOMO) level with respect to the metal Fermi level (EF) almost accords with the variation in [uppercase_phi_synonym]m. For BCP on Ag, Mg, and Ca, whose [uppercase_phi_synonym]m is below 4.3 eV, the HOMO energy level is fixed at 3.7 eV with respect to EF regardless of [uppercase_phi_synonym]m and new electronic states, called gap states, appeared at BCP/metal interfaces. Since the appearance of gap states is correlated with the energy of the lowest unoccupied molecular orbital (LUMO) level with respect to EF, these states appear to have formed mainly through the interaction with the LUMO. A clear correlation between the density of the gap states and the vacuum level shift suggesting a charge redistribution at BCP/metal interfaces was found. The energy shift in the gap states, which may originate from the variation in the electron occupation of the states, directly affected the electronic conductivity of metal-doped BCP layers (doping metal=Au, Ag, and Ca). These results suggest the electron transfer from the metal EF to gap states plays an influential role in the electrical properties at BCP/metal interfaces. [ABSTRACT FROM AUTHOR]

Photoelectrical measurements were taken on a nominally undoped-InGaP/GaAs superlattice, inserted between two p+ and n+ InGaP cladding layers. The sequence of InGaP/GaAs alternated layers forming the superlattice was grown lattice matched on n+-GaAs substrates through low pressure-metal organic vapor phase epitaxy, at growth conditions previously optimized for obtaining sharp interfaces and negligible ordering effects in the cation sublattice of the InGaP layers. A peculiar dependence of both the photocurrent and the photovoltaic signals on the modulation frequency of the exciting light beam was observed and then interpreted according to proper equivalent electrical circuits. The effects induced by an incomplete depletion of the nominally undoped superlattice region are analyzed in detail, and the analogies between photoelectrical investigation and admittance spectroscopy are pointed out. [ABSTRACT FROM AUTHOR]

The feasibility of cascaded second harmonic generation (SHG) and third harmonic generation (THG) in a monolithic two-sectioned periodically poled lithium tantalate crystal is analyzed. Simulation using a computational nonlinear optical model rigorously coupled with a thermal model suggests that 25%–30% THG efficiency can be achieved for a 3 W 20 ns pulsed 1.064 μm laser operating at 10 kHz if the crystal is composed of two sections: (i) ≈8.0 μm period first-order SHG structure and (ii) ≈6.6 μm period third-order THG structure. Significant inhibition of THG efficiency arises due to absorption of SH and TH, the heat release along the crystal, and associated thermal dephasing and lensing which can be effectively compensated by decreasing the temperature of the operating crystal below the quasiphase matching temperature. Corrections for the energy exchange lengths for optimal SHG and THG section design are suggested. [ABSTRACT FROM AUTHOR]

By antimony doping tin oxide, SnO2:Sb (ATO), below 1.0% Sb concentration, controllable n-type doping was realized. Plasma-assisted molecular beam epitaxy has been used to grow high quality single crystalline epitaxial thin films of unintentionally doped (UID) and Sb-doped SnO2 on r-plane sapphire substrates. A UID thickness series showed an electron concentration of 7.9×1018 cm-3 for a 26 nm film, which decreased to 2.7×1017 cm-3 for a 1570 nm film, whereas the mobility increased from 15 to 103 cm2/V s, respectively. This series illustrated the importance of a buffer layer to separate unintentional heterointerface effects from the effect of low Sb doping. Unambiguous bulk electron doping was established by keeping the Sb concentration constant but changing the Sb-doped layer thickness. A separate doping series correlated Sb concentration and bulk electron doping. Films containing between 9.8×1017 and 2.8×1020 Sb atoms/cm3 generated an electron concentration of 1.1×1018–2.6×1020 cm-3. As the atomic Sb concentration increased, the mobility and resistivity decreased from 110 to 36 cm2/V s and 5.1×10-2 to 6.7×10-4 Ω cm, respectively. The Sb concentration was determined by secondary ion mass spectrometry. X-ray diffraction and atomic force microscopy measurements showed no detrimental effects arising from the highest levels of Sb incorporation. Temperature dependent Hall measurements established a lower limit for the Sb electron activation energy of 13.2 meV and found that films with greater than 4.9×1019 electrons/cm3 were degenerately doped. Within experimental uncertainties, 100% donor efficiency was determined for Sb-doped SnO2 in the range studied. [ABSTRACT FROM AUTHOR]

Optical properties of directly excited erbium (Er3+) ions have been studied in silicon rich silicon oxide materials codoped with Er3+. The spectral dependence of the direct excitation cross section (σdir) of the Er3+ atomic 4I15/2→4I11/2 transition (around 0.98 μm) has been measured by time resolved μ-photoluminescence measurements. We have determined that σdir is 9.0±1.5×10-21 cm2 at 983 nm, at least twice larger than the value determined on a stoichiometric SiO2 matrix. This result, in combination with a measurement of the population of excited Er3+ as a function of the pumping flux, has allowed quantifying accurately the amount of optically active Er3+. This concentration is, in the best of the cases, 26% of the total Er population measured by secondary ion mass spectrometry, which means that only this percentage could provide optical gain in an eventual optical amplifier based on this material. [ABSTRACT FROM AUTHOR]

Highly p-doped regions in multicrystalline silicon solar cells, such as the back surface field region, are analyzed by means of small angle beveling and micro-Raman spectroscopy. Small angle beveling and subsequent Secco etching are used to enhance the lateral resolution of the micro-Raman spectroscopic measurements and to investigate the microstructure of the back surface field region in detail. The position-dependent analysis of the free carrier concentrations within the back surface field region is based on the Raman specific Fano resonances. The Raman spectroscopic measurement results are compared to results obtained from electrochemical capacitance-voltage measurements, which allows a subsequent calibration of the Raman data for the quantitative analysis of the free carrier concentrations within the highly p-doped regions of silicon solar cells and other devices. Our investigations show that the free carrier as well as the dopant concentration profiles within the back surface field region exhibit a nearly step-functional shape instead of the extended gradient shape which the electrochemical capacitance-voltage measurements suggest. Moreover, we show that the shape of the back surface field is often influenced by grain boundaries and other defects that occur in multicrystalline silicon wafers. [ABSTRACT FROM AUTHOR]

The effects of boron and arsenic doping in β-FeSi2 have been studied by theoretical simulations and electrical characterization. First-principles calculations revealed that B and As were energetically favorable to occupy the SiII and SiI sites, respectively. The impurity doping was found to induce structural relaxation via lattice distortion, with As doping causing elongation of the As­Si bonds and contraction of the As–Fe bonds while B doping resulting in both inward and outward relaxations of the neighboring Si and Fe host atoms. p-type and n-type conductivities were suggested for the B- and As-doped β-FeSi2, respectively, and confirmed experimentally by Hall effect measurements. B and As were shown to introduce shallow impurity levels in the forbidden gap of β-FeSi2 and therefore could be effective dopants for β-FeSi2. A carrier concentration in a tunable range of 1017 cm-3 and a mobility in the order of 100 cm2/V s were consistently obtained. [ABSTRACT FROM AUTHOR]

Gallium arsenide layers doped with high concentrations of Be and Si by molecular-beam epitaxy are studied by photoluminescence (PL) spectroscopy. PL peaks from doped layers are observed at energies significantly lower than the band-gap of GaAs. The growth and doping conditions suggest that the origin of these peaks is different from that of low energy PL peaks, which were observed in earlier studies and attributed to impurity-vacancy complexes. The dependence of the peak energy on the temperature and the annealing is found to differ from that of the peaks attributed to impurity-vacancy complexes. On the basis of these observations, it is suggested that the low energy peaks are attributed to short range ordered arrangements of impurity ions. This possibility is examined by calculations of the PL spectra with models of pairs of acceptor and donor delta-doped layers and PL experiments of a superlattice of pairs of Be and Si delta-doped layers. [ABSTRACT FROM AUTHOR]

Theoretical investigation of the defect energy levels in band gap for ZnO is of great importance to understand the photoluminescence (PL) spectrum in experiment. However, the “band-gap” problem in the density functional calculations leads to incorrect evaluation of the defect levels inside the band gap. In this work, we perform hybrid density functional calculation, which can accurately predict the band gap width and the gap states, to study the electronic structures of both native defects and doped impurities of Li, Na, K, and Ag in ZnO. Our results show that both the vacancies and octahedral self-interstitials of O and Zn contribute to the broad green PL spectrum observed in experiments. In addition, the gap states arising from these doped impurities are predicted, where some of the gap states match with the experimental values. Moreover, the characters of these gap states are discussed based on the calculated density of states. [ABSTRACT FROM AUTHOR]

We report a systematic density-functional theory investigation of the “structure-property relationship” of Cr:AlN by doping up to 5 Cr atoms in large supercells, for which exhaustive structural and magnetic configurations have been calculated—including full atomic relaxation. Our results demonstrate that the Cr atoms tend to segregate to form Cr-N-Cr bonded clusters, which are embedded in the AlN host wurtzite structure. Significantly, while the ferromagnetic state with a spin moment close to 3 μB/Cr is the ground state for both isolated “single” and “pair” doping configurations, for larger cluster configurations states containing antiferromagnetic or ferrimagnetic coupling with net spin in the range of 0-1.53 μB/Cr are found to be energetically more favorable. Electrical conductivity (half-metallic or insulating) is predicted to be sensitively dependent on the dopant concentration. We propose a picture that various sized Cr-N-Cr bonded clusters coexist and the statistical distribution and associated magnetic properties will depend sensitively on the growth conditions. Such a scenario is in agreement with recent experiments and can help understand a number of hitherto puzzling experimental observations, notably the low mean saturation magnetic moment, the contracted lattice constants, and the highly insulating behavior. [ABSTRACT FROM AUTHOR]

The intermolecular potentials for the NO(X 2Π)–Kr and NO(A 2Σ+)–Kr systems have been calculated using highly accurate ab initio calculations. The spin-restricted coupled cluster method for the ground 1 2A′ state [NO(X 2Π)–Kr] and the multireference singles and doubles configuration interaction method for the excited 2 2A′ state [NO(A 2Σ+)–Kr], respectively, were used. The potential energy surfaces (PESs) show two linear wells and one that is almost in the perpendicular position. An analytical representation of the PESs has been constructed for the triatomic systems and used to carry out molecular dynamics (MD) simulations of the NO-doped krypton matrix response after excitation of NO. MD results are shown comparatively for three sets of potentials: (1) anisotropic ab initio potentials [NO molecule direction fixed during the dynamics and considered as a point (its center of mass)], (2) isotropic ab initio potentials (isotropic part in a Legendre polynomial expansion of the PESs), and (3) fitted Kr–NO potentials to the spectroscopic data. An important finding of this work is that the anisotropic and isotropic ab initio potentials calculated for the Kr–NO triatomic system are not suitable for describing the dynamics of structural relaxation upon Rydberg excitation of a NO impurity in the crystal. However, the isotropic ab initio potential in the ground state almost overlaps the published experimental potential, being almost independent of the angle asymmetry. This fact is also manifested in the radial distribution function around NO. However, in the case of the excited state the isotropic ab initio potential differs from the fitted potentials, which indicates that the Kr–NO interaction in the matrix is quite different because of the presence of the surrounding Kr atoms acting on the NO molecule. MD simulations for isotropic potentials reasonably reproduce the experimental observables for the femtosecond response and the bubble size but do not match spectroscopic results. A general overall view of the results suggests that, when the Kr–NO interaction takes place inside the matrix, potentials are rather symmetric and less repulsive than those for the triatomic system. [ABSTRACT FROM AUTHOR]

We report on the results of a complex study of electrical (77-300 K) and luminescence (10-300 K) properties of n-ZnSe single crystals annealed in a Zn melt containing Al impurity at concentrations ranging from 0.1 to 80 at. %. It was established that Al atoms form donor centers only at a low impurity concentration (≤0.5 at. %). The increase of the amount of Al atoms in the crystal results in the formation of (VZnAlZn) associative acceptor centers leading to the self-compensation of the shallow Al donor impurity. This process is accompanied by the emergence and development of a self-activated luminescence band associated with the (VZnAlZn) acceptor centers. We show that further increase of the Al content in the melt (≥10 at. %) leads to the dissociation of the acceptor complexes and to a recurrent donor doping effect. The photoluminescence spectra of such crystals are dominated by activated luminescence via the (CuZnVSeCui) and (CuZnAlZn) associative centers. [ABSTRACT FROM AUTHOR]

The band structure of a single-walled carbon nanotube (SWNT)/metal system, including a shift in the vacuum level which appears at the SWNT/metal interface, was characterized by using a Kelvin-probe force microscopy method. In the SWNT/gold system, the shift (Δ) of the vacuum level was observed to be +5.2 meV, which is one order of magnitude smaller than previously observed. When we carried out carrier doping of the SWNTs, the observed Δ was downshifted from +5.2 to -52 meV, which introduced some upshift in the band structure of the doped SWNTs. This change induced easier hole injection, which coincides with the field effect transistor characteristics of undoped and doped SWNT transistors. A similar analysis was also carried out for a SWNT/ferromagnet system. [ABSTRACT FROM AUTHOR]

The electronic properties of nitrogen doped Mo(110) surfaces were investigated using the first-principles pseudopotential method within the local density approximation in order to determine the effect of doping on the work function. Nitrogen doping was modeled by adsorbing N in both surface and subsurface positions. Surface adsorption of nitrogen was found to increase the work function by as much as 2 eV due to the negative surface dipole induced by the electronegativity of nitrogen. Subsurface doping of nitrogen is energetically similar to surface adsorption, but has a small effect on the work function and only when within the first two to three surface Mo layers. [ABSTRACT FROM AUTHOR]

We have studied the electronic properties of delta-doped In0.22Ga0.78As/GaAs quantum wells (QWs) by van der Pauw Hall measurements and Shubnikov–de Haas measurements. From the temperature-dependent van der Pauw Hall measurements, we observed two kinds of donors, which have binding energies of 104±7 and 9.6±0.1 meV. After inserting In0.1Ga0.9As layers between the In0.22Ga0.78As and GaAs layers, a single donor with binding energy of 50±2 meV was observed. The carrier concentration determined by SdH measurements did not change after the QWs were illuminated at low temperature, which indicates that these deep donors could not produce a persistent photoconductivity in delta-doped In0.22Ga0.78As/GaAs QWs. [ABSTRACT FROM AUTHOR]

Here we report the doping effect of blue light-emitting electron transport molecules on the performance of blue organic light-emitting devices (OLEDs). 4,4′-N,N′-dicarbazole-biphenyl (CBP) was chosen as a blue emission material (layer) for two main reasons: its wide band gap makes it suitable for blue emission; and its shifted energy band structure allows for easy electron injection. However, the main drawback of CBP is the low electron mobility and the large hole injection barrier. In order to overcome these weak points, the CBP nanolayer (50 nm thick) in blue OLEDs has been doped with 2-(2-hydroxyphenylbenzoxazole) lithium (LiPBO), which is known to be a blue light-emitting electron transport material. The result showed that the device performance (charge injection voltage, turn-on voltage, and current efficiency) was improved by doping the LiPBO molecule, an improvement that can be attributed to the enhanced electron mobility and the reduced hole injection barrier of the LiPBO-doped CBP nanolayer. However, the blue color purity of OLEDs marginally deteriorated as a result of the LiPBO doping. The worst Commission Internationale de l'Eclairage (CIE) color coordinate of OLEDs was x=0.16 and y=0.18 at 16 V, while the standard coordinates are x=0.14 and y=0.08, which is possibly due to the formation of exciplexes in a nanoscale. [ABSTRACT FROM AUTHOR]

We investigate how low concentrations of N impurities (x<1%) modify the electrical and optical properties of a GaAs/AlAs superlattice positioned in the intrinsic i region of a p-i-n diode. Increasing x from 0% to 0.9% enhances the integrated intensity of the low temperature electroluminescence emission from the superlattice by more than a factor of 104. We attribute this behavior to reduced transmission of electrons through the superlattice due to the N-induced carrier localization. [ABSTRACT FROM AUTHOR]

X-ray diffraction measurements, utilizing multiple and single diffraction methods, were used to examine lattice compression of magnesium doped (approximately 100 ppm) LiF single crystals shocked along the [100] direction. Unlike ultrapure LiF crystals, examined in previous x-ray diffraction studies, magnesium doped crystals display large elastic wave amplitudes under shock wave compression. Analysis of multiple diffraction data from the (200) and (202) planes and single diffraction data from the (200) planes showed that the crystal lattice for doped crystals was compressed isotropically in the peak state, similar to that observed for ultrapure crystals. This agreement demonstrates that the large elastic wave amplitude and subsequent stress relaxation observed in wave propagation measurements for the doped LiF crystals are a transient phenomenon and do not appear to affect the lattice compression in the final state. Implications of this finding are discussed. [ABSTRACT FROM AUTHOR]

A series of polycrystalline bulk samples of Mg1-2x(AgAl)xB2 (0.0%<=x<=1.0%) has been synthesized by a solid state reaction method. The structure, Raman spectrum, and superconducting properties have been investigated by x-ray diffraction, Raman spectroscopy, and low-temperature resistivity measurements. It is found that the Ag, Al double doping causes the expansion of crystal lattice along the a- and c-axis orientations due to the substitution inducing ionic size variation. A redshift of peak position is observed in Raman spectra, which is ascribed to the crystal cell volume change inducing the variation of the phonon frequency. The superconducting transition temperature (Tc) is degressive with the doping level (x) increase. By the Ag and Al double doping, the hole concentration is kept to be unchanged in MgB2, which eliminates the effects of the charge carrier concentration change and band filling on Tc. It is suggested that the reason of the Tc suppression caused by the double doping is the co-operating results of the disorder effect and the chemical pressure effect induced by the chemical substitution. [ABSTRACT FROM AUTHOR]

This work presents the in-plane thermal-conductivity data for pure as well as boron-doped (1.6×1021/cm3), arsenic-doped (2.3×1020/cm3), and phosphorus-doped (2.3×1020/cm3) silicon layers of thickness 30 nm in the temperature range of 300–450 K. The steady-state Joule heating and electrical resistance thermometry are used to measure the lateral thermal conductivity of suspended silicon layers. Thermal-conductivity data for pure and doped single-crystalline thin silicon layers can be interpreted using thermal-conductivity integral in relaxation-time approximation that accounts for phonon-boundary and phonon-impurity scatterings. No additional fitting parameters are used in this work in contrast with previous studies that required an unusually large phonon-impurity scattering coefficient to fit the thermal-conductivity data for bulk doped silicon to the predictions of the thermal-conductivity integral in relaxation-time approximation. [ABSTRACT FROM AUTHOR]

Dielectric measurements were carried out on specimens with compositions BaO.(6-x)Fe2O3.x Sb2O3 with x having values of 0.0, 0.025, 0.1, and 0.3. Sb2O3 doping increases the dielectric permittivity drastically. Two loss peaks of similar activation energies were observed. The analysis showed that these arose because of the presence of Fe2+–Fe3+ and Sb3+–Sb5+ pairs, respectively, in the system. The experimental data could be analyzed satisfactorily in terms of Cole-Cole relaxation formalism. The relaxation distribution parameter α was found to be much larger in the case of Sb3+–Sb5+ pair than that due to Fe2+–Fe3+ pair. [ABSTRACT FROM AUTHOR]

The influence of operation voltages and doping densities on superlattice infrared photodetectors (SLIPs) with a single current blocking layer has been investigated. Higher responsivity and the redshift of peak-responsivity wavelength with increasing applied voltage are observed for SLIP with higher quantum-well doping. The phenomenon is attributed to the increase in tunneling probability for low-energy photoelectrons with increased applied voltage. Taking into consideration the shift in Fermi level at different doping densities in the quantum well and the electron-tunneling probability for the front blocking layer, the spectral responses under different applied voltages can be derived by the summation of dipole transitions for each energy states in the minibands. It is shown that the measurement data and the simulation results are identical for devices applied under different voltages and with different quantum-well doping densities. [ABSTRACT FROM AUTHOR]

We prepared polycrystalline samples of β-KxBa1-xCu2S2 (x=0,0.05,0.1) with a natural superlattice structure and measured the thermoelectric properties from room temperature to about 850 K. The Seebeck coefficients are positive in the whole temperature range. The electrical resistivity and Seebeck coefficient decrease with potassium content, which indicates that potassium doping introduces charge carriers. The thermal conductivities of potassium-doped samples are slightly higher than those of undoped samples as a result of electronic contributions. The values of thermal conductivities are very low, 0.97 W m-1 K-1 at room temperature for β-K0.1Ba0.9Cu2S2. The dimensionless figure of merit ZT can be improved by potassium doping and reaches 0.28 at 820 K for β-K0.1Ba0.9Cu2S2. [ABSTRACT FROM AUTHOR]

Heteroepitaxial growth behavior of Mn-doped ZnO thin films (Zn[sub 1-x]Mn[sub x]O) on Al[sub 2]O[sub 3] (0001) substrates by pulsed laser deposition was investigated particularly as a function of Mn content (0.00<=x<=0.35) using synchrotron x-ray scattering and atomic force microscopy. The undoped ZnO film was grown epitaxially with a 30° rotation of ZnO basal planes with respect to the Al[sub 2]O[sub 3] substrate while having a small amount of grains with another epitaxial relationship, i.e., the hexagon-on-hexagon growth. A small amount of Mn doping (x=0.05) not only greatly improved the atomic alignment both in the in-plane and in the out-of-plane directions, but also led to a singly oriented film by totally suppressing the hexagon-on-hexagon growth. With further incorporation of Mn into ZnO beyond that content, the epitaxial nature again deteriorated. The superior epitaxial growth of the film with an optimum Mn content is attributed to the formation of much larger grains in it. In addition, our Mn-doped ZnO thin films showed a paramagnetic behavior. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Results are reported on p-GaAs homojunction interfacial work function internal photoemission far infrared (HIWIP FIR) detectors with a ∼ 10[SUB19] cm[SUB-3] carbon doped single emitter and a barrier layer for three different barrier thicknesses. A remarkably high quantum efficiency with low dark current and an increased responsivity were observed the devices with 1-, 0.1-, and 4-μm-thick barrier regions. The dark current densities for these structures are on the order of 1 - 10 μA/cm[SUB2] at 4.2 K, corresponding to a high dynamic resistance compared with previous HIWIP FIR detectors. A detector with a barrier thickness of 1 μm had a peak responsivity of 18.6 A/W, a peak detectivity D*= 9 × 10[SUB11] cm Hz√ /W, and a quantum efficiency of 40% at a wavelength of 58 μm under a reverse bias measured at 4.2 K. Cutoff wavelengths of these detectors vary with bias and are around 70 μm as expected. The main features of the absorption and responsivity spectra are well described based on a model incorporating free carrier absorption, hot hole transport, and emission over the barrier. [ABSTRACT FROM AUTHOR]

The effect of charging on the longitudinal second hyperpolarizability of polyacetylene (PA) chains containing up to nearly 70 carbon atoms has been investigated ab initio by characterizing chains with and without an explicit alkali atom (Li, Na, K) as dopant. Whereas charging dramatically enhances the static electronic and vibrational hyperpolarizabilities, γ[sup e][sub L](0) and γ[sup v][sub L], of an isolated chain at intermediate chain lengths, the presence of an alkali atom counterion substantially reduces this effect. As the size of the alkali atom increases, most properties, including the hyperpolarizabilities, approach those of the isolated chain. Detailed analysis shows that the behavior of γ[sup e][sub L](0) is most simply explained in terms of a reduced electrostatic pinning potential due to increased distance between chain and counterion. At all chain lengths studied γ[sup e][sub L](0) of PA is enhanced by alkali doping. For chains containing 50 carbon atoms (N[sub C] = 50), the increase due to K doping is about 9 x 10[sup 7] a.u., which more than doubles the value for an undoped chain of similar length. The normalized quantity γ[sup e][sub L](0)/N[sub C] exhibits a maximum for the isolated soliton (at about N[sub C] = 61) that is over four times that of the infinite undoped (and unbent) chain. When the alkali dopant is taken into account this maximum diminishes considerably and shifts to larger N[sub C] than we have considered. In comparison with the maximum for the undoped species (at N[sub C] = ∞) there is a small enhancement of γ[sup e][sub L](0)/N[sub C] for K doping, but none for either Li or Na doping at the coupled-perturbed Hartree—Fock (CPHF)/6-31G level of theory. Intermediate length isolated chains bearing a charged soliton show order of magnitude increases in γ[sup v] for the degenerate four-wave mixing (DFWM) and, especially, electric field-induced second harmonic generation (dc-SHG)... [ABSTRACT FROM AUTHOR]

Sb doped PbWO[sub 4] (Sb:PWO) shows unique features in its dielectric and visible spectra. We propose that, in low concentration, the dopant enters the lattice as interstitial ions, and at high level it also substitute for W[sup 6+] sties. The existence of interstitial ions with relatively high mobility leads to non-negligible dc conductivity, whereas the substitutional impurity produces O[sub 2][sup 3-] color centers, which results in absorption at 420 nm, as well as holes hopping among oxygen ions in the Sb–O tetrahedra, that is the origin for the observed dielectric relaxation with an unusually low activation energy of 30±2 meV. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We propose a contact structure for InAs/GaSb multilayers, such that electrons and holes are selectively injected in alternating layers. This enables the implementation of a far-infrared lateral current injection laser based on the InAs/GaSb superlattice. Preliminary calculation of the gain shows that both surface- and edge-emitting designs are possible. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The properties of p-AlGaN/GaN modulation doped superlattices (SLs) prepared by molecular beam epitaxy were studied by means of conductivity versus temperature, admittance spectroscopy, photoinduced current spectroscopy, microcathodoluminescence (MCL) spectra measurements, and measurements of effective diffusion lengths. It is shown that in SLs grown on GaN underlayers the sheet resistivity is about two orders of magnitude lower than for reference p-GaN films and the resistivity of SLs remains lower up to temperatures of about 350 °C. For SLs grown on AlGaN underlayers the gain in resistivity is much more moderate and certain advantages in using such SLs are envisaged only for temperatures below room temperature. The reason for this lower gain is a considerable decrease in hole mobility compared to p-GaN. The effect is somewhat tentatively attributed to worse crystalline perfection of these SLs. It is also shown that such SLs are characterized by a strongly broadened MCL peak and the presence of additional hole traps with activation energy of about 0.4 eV. Despite that, the photosensitivity and MCL intensity of these SLs are much better than for reference p-GaN samples. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The presence of chromium impurities in the crystal matrix of chromium-doped KTiOPO is shown to be at the origin of a strong cubic optical nonlinearity of this material. As a result, a pronounced self-phase modulation of a Gaussian laser beam at 532 nm is observed in the far field as a diffraction pattern consisting of alternating dark and bright rings. The induced nonparabolic and polarization sensitive refractive index change is also used to modulate a weak probe laser beam at 633 nm. A simple theoretical model incorporating a laser heating process and a thermo-optical effect accounts for the main features observed in our experiments and elucidates the mechanisms leading to the diffraction pattern formation. c 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Two kinds of silicon samples have been used in this work: one containing a sequence of boron spikes and one with a sequence of alternating boron and antimony spikes, both grown by molecular beam epitaxy. These samples were irradiated with 2.5 MeV protons at an elevated temperature ranging from 500 to 830 °C and characterized by secondary-ion-mass spectrometry. The energy of the proton beam was chosen such that the generation rate of point defects can be considered as uniform throughout the delta-doped Si samples. The influence of the sample surface and of the boron concentration (ranging from 5x10[sup 15] to 3.2x10[sup 18] B/cm[sup 3] in the different samples) on the diffusion of boron have been studied in detail. The effect of antimony on boron diffusion has also been analyzed. For each sample, the B diffusion coefficient is increased under irradiation as compared to the B diffusion coefficient in unirradiated areas. This enhancement is dependent on the irradiation temperature, on the position of the boron spike and on the boron concentration. Further, the presence of antimony enhances the boron diffusion during low-temperature proton irradiation. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Boron was implanted with four energies and doses at 400 °C into 6H-SiC epilayers to form a 500 nm thick doped layer with a mean concentration between 1x10[sup 18] and 1.5x10[sup 21] cm[sup -3]. Two annealing techniques were used: furnace and flash lamp annealing. The electrical and microstructural effects were investigated using temperature dependent Hall measurements, cross sectional electron microscopy, and secondary ion mass spectrometry. During the annealing two competing processes occurred: boron outdiffusion and growth of boron containing precipitates. The efficiency of these individual processes is different for varying dopant concentrations as well as annealing techniques. After furnace annealing at temperatures between 1550 and 1750 °C and for a mean boron concentration of 5x10[sup 19] cm[sup -3] boron containing clusters are found mainly around the region of the three deeper implantation peaks. In the surface region boron outdiffusion is observed adjusting a concentration of 1.5x10[sup 19] cm[sup -3]. Using flash lamp annealing, the outdiffusion is negligible. For high dopant concentrations (1.5x10[sup 21] cm[sup -3]) the growth of random distributed boron precipitates is the dominating effect independent of the used annealing techniques. The electrical activation is limited due to the solubility of boron in SiC. After furnace annealing Hall effect measurements show a maximum hole concentration of about 2x10[sup 16] cm[sup -3] for the boron concentration of about 5x10[sup 18] cm[sup -3]. Alternative to the furnace annealing, the electrical properties after flash lamp annealing at about 2000 °C, 20 ms show a slight enhancement of the maximum hole concentration for boron concentrations <3x10[sup 20] cm[sup -3]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study of the lattice-matched and strained doped-channel field-effect transistors to investigate the influence of the indium content in the channel on device properties. Crystal growth and device technology; Direct current characteristics; Microwave characteristics; Conclusion.

The aim of this work is to investigate the temperature dependences both in CuO2 plane and out-of plane resistivities in electron-doped Nd2-xCexCuO4 for x from 0.135 up to 0.15 in order to analyze the anisotropy of the electrical transport in the process of the evolution from antiferromagnetic order in the underdoped region to superconducting order in optimally doped region. [ABSTRACT FROM AUTHOR]

Reports on the use of room-temperature photoluminescence to characterize modulation-doped AlGaAs/InGaAs/superlattice strained later quantum wells. Sample preparation; Details of the line-shape model.

Presents a study that determined band structures of n-i-n-i doping superlattices using a self-consistent calculation based on the envelope function formalism. Calculation procedure for modulation potentials, charge density distributions and dispersion relationships; Potential modulation and density of states of n-i-n-i doping superlattices; Effect of the thickness of the doped region and temperature on the electrical properties of n-i-n-i doping superlattices.

Presents information on a study that investigated the reduction in the series resistance of distributed Bragg reflectors both experimentally and theoretically. Discussion on experimental results for series resistance with quasi-graded superlattices at the heterointerfaces; Examination on the dependence of series resistance on doping concentration and temperature; Method for further reduction in the series resistance.

Provides information on a study that determined the change in lattice constant when single-crystal silicon is substitutionally doped with boron. Details on the analysis of diffractometric measurements; Experimental techniques used; Results and discussion on the study; Conclusions.