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1.	Johansson, MP, et al. (author) Template-synthesized BN : C nanoboxes 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:7, s. 825-827 Journal article (peer-reviewed)abstract Box-shaped nanostructures of B-C-N compounds were synthesized by reactive sputtering of boron carbide in mixed argon and nitrogen discharges. Transmission electron microscopy showed that these nanoboxes were grown on self-patterned NaCl substrate with projected areas ranging from similar to 1x10(2) to similar to 5x10(4) nm(2), sizes 50-100 nm, and number density similar to 100 mu m(-2). Electron energy loss spectroscopy revealed a phase separation of BN and C:N layers. (C) 2000 American Institute of Physics. [S0003-6951(00)00507-6].
2.	Gahn, C, et al. (author) Generating positrons with femtosecond-laser pulses 2000 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:17, s. 2662-2664 Journal article (peer-reviewed)abstract Utilizing a femtosecond table-top laser system, we have succeeded in converting via electron acceleration in a plasma channel, low-energy photons into antiparticles, namely positrons. The average intensity of this source of positrons is estimated to be equivalent to 2x10(8) Bq and it exhibits a very favorable scaling for higher laser intensities. The advent of positron production utilizing femtosecond laser pulses may be the forerunner to a table-top positron source appropriate for applications in material science, and fundamental physics research like positronium spectroscopy. (C) 2000 American Institute of Physics. [S0003-6951(00)00143-1].
3.	Paul, DJ, et al. (author) Si/SiGe electron resonant tunneling diodes 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:11, s. 1653-1655 Journal article (peer-reviewed)abstract Resonant tunneling diodes have been fabricated using strained-Si wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.8Ge0.2 n-type substrate, which demonstrate negative differential resistance at 298 K. Peak current densities of 5 kA/cm(2) with peak-to-valley current ratios of 1.1 have been achieved. Theoretical modeling of the structure demonstrates that the major current peak results from the tunneling of light-mass electrons from the relaxed substrate and not from the heavy-mass electrons in the emitter accumulation layer. (C) 2000 American Institute of Physics. [S0003- 6951(00)02337-8].
4.	Wahab, Qamar Ul, et al. (author) Influence of epitaxial growth and substrate-induced defects on the breakdown of 4H-SiC Schottky diodes 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:19, s. 2725-2727 Journal article (peer-reviewed)abstract Morphological defects and elementary screw dislocations in 4H-SiC were studied by high voltage Ni Schottky diodes. Micropipes were found to severely limit the performance of 4H-SiC power devices, whereas carrot-like defects did not influence the value of breakdown voltage. The screw dislocation density as determined by x-ray topography analysis under the active area of the diode was also found to directly affect the breakdown voltage. Only diodes with low density of screw dislocations and free from micropipes could block 2 kV or higher. (C) 2000 American Institute of Physics. [S0003-6951(00)01119-0].
5.	Stafström, Sven (author) Reactivity of curved and planar carbon-nitride structures 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:24, s. 3941-3943 Journal article (peer-reviewed)abstract The reactivity of different carbon-nitride structures has been studied using density functional theory calculations. The studies involve C59N and clusters of curved and planar CNx structures. Nitrogen is shown to lower the energy of pentagon defects in the graphite like structures, whereas heptagons are unlikely to be present. From this observation, it follows that nitrogen stimulates growth of fullerene like structures in CNx. The presence of nitrogen also increases the reactivity of the carbon atoms around the nitrogen. This leads to cross linking between basal planes which can explain the hardness and elasticity of CNx films. (C) 2000 American Institute of Physics. [S0003-6951(00)03751-7].
6.	Pozina, Galia, et al. (author) Optical spectroscopy of GaN grown by metalorganic vapor phase epitaxy using indium surfactant 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:23, s. 3388-3390 Journal article (peer-reviewed)abstract The effect of In surfactant during metalorganic vapor phase epitaxial growth on sapphire substructure on the properties of GaN layers is studied using time-resolved photoluminescence. cathodoluminescence. and scanning electron microscopy. The samples are divided into two groups. where hydrogen and nitrogen, respectively, have been used as a carrier gas during growth. It is shown that In-doped samples have a lower dislocation density, a narrower photoluminescence linewidth, and a longer foe exciton lifetime. The influence of indium is stronger for GaN layers grown in nitrogen-rich conditions. The improvements of structural and optical properties are attributed to the effect of In on dislocations. (C) 2000 American Institute of Physics. [S0003-6951(00)02723-6].
7.	Valcheva, E, et al. (author) Interface structure of hydride vapor phase epitaxial GaN grown with high-temperature reactively sputtered AlN buffer 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:14, s. 1860-1862 Journal article (peer-reviewed)abstract Thick hydride vapor phase epitaxy GaN layers have been grown on a-plane sapphire using high-temperature ion-assisted reactively sputtered AlN as a buffer layer. Transmission electron microscopy and atomic force microscopy were carried out to study the formation of the two interfaces sapphire/AlN and AlN/GaN, and their influence on the microstructure of both the buffer layer and the main GaN layer. It was demonstrated that the high-temperature reactively sputtered buffer layer provides a good alternative for hydride vapor phase epitaxy growth of GaN layers. In particular, the buffer promotes a specific interface ordering mechanism different from that observed on low-temperature buffers. (C) 2000 American Institute of Physics. [S0003-6951(00)00314-4].
8.	Alnis, J, et al. (author) Sum-frequency generation with a blue diode laser for mercury spectroscopy at 254 nm 2000 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:10, s. 1234-1236 Journal article (peer-reviewed)abstract Blue diode lasers emitting 5 mW continuous-wave power around 400 nm have recently become available. We report on the use of a blue diode laser together with a 30 mW red diode laser for sum-frequency generation around 254 nm. The ultraviolet power is estimated to be 0.9 nW, and 35 GHz mode-hop-free tuning range is achieved. This is enough to perform high-resolution ultraviolet spectroscopy of mercury isotopes. The possibility to use frequency modulation in the ultraviolet is demonstrated; however, at present the ultraviolet power is too low to give advantages over direct absorption monitoring. Mercury detection at atmospheric pressure is also considered which is of great interest for environmental monitoring. (C) 2000 American Institute of Physics. [S0003-6951(00)02810-2].
9.	Schneider, Jochen, et al. (author) Magnetic-field-dependent plasma composition of a pulsed arc in a high-vacuum ambient 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:12, s. 1531-1533 Journal article (peer-reviewed)abstract The effect of a magnetic field on the plasma composition of a pulsed Au plasma stream in a high-vacuum ambient is described. The plasma was formed with a pulsed vacuum-arc-plasma source, and the time-resolved plasma composition was measured with time-of-flight charge-to-mass spectrometry. Plasma impurities due to ionization of nonmetallic species (H+, O+, and N+) were found to be below the detection limit in the absence of a magnetic field. However, in the presence of a magnetic field (0.4 T), the contribution of ionized nonmetal species to the plasma composition was up to 0.22 atomic ratio. These results are characteristic of plasma-based techniques where magnetic fields are employed in a high-vacuum ambient. In effect, the impurity incorporation during thin-film growth pertains to the present findings. (C) 2000 American Institute of Physics. [S0003-6951(00)00712-9].
10.	Tungasmita, Sukkaneste, et al. (author) Enhanced quality of epitaxial AlN thin films on 6H-SiC by ultra-high-vacuum ion-assisted reactive dc magnetron sputter deposition 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:2, s. 170-172 Journal article (peer-reviewed)abstract Epitaxial AlN thin films have been grown on 6H-SiC substrates by ultra-high-vacuum (UHV) ion-assisted reactive dc magnetron sputtering. The low-energy ion-assisted growth (E-i = 17-27 eV) results in an increasing surface mobility, promoting domain-boundary annihilation and epitaxial growth. Domain widths increased from 42 to 135 nm and strained-layer epitaxy was observed in this energy range. For E-i> 52 eV, an amorphous interfacial layer of AlN was formed on the SiC, which inhibited epitaxial growth. Using UHV condition and very pure nitrogen sputtering gas yielded reduced impurity levels in the films (O: 3.5 x 10(18) cm(-3)). Analysis techniques used in this study are in situ reflection high-energy electron diffraction, secondary-ion-mass spectroscopy, atomic-force microscopy, x-ray diffraction, and cross-section high-resolution electron microscopy. (C) 2000 American Institute of Physics. [S0003-6951(00)01802-7].
11.	Pozina, Galia, et al. (author) InGaN/GaN multiple quantum wells grown by metalorganic vapor phase epitaxy with mass transport 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:11, s. 1638-1640 Journal article (peer-reviewed)abstract We report on studies of In0.12Ga0.88N/GaN heterostructures with three 35-Angstrom-thick quantum wells (QWs) grown on sapphire substrates by metalorganic vapor phase epitaxy with employment of mass transport. The structure is demonstrated to show good structural and optical properties. The threading dislocation density is less than 10(7) cm(-2) for the mass-transport regions. The photoluminescence (PL) spectrum is dominated by the rather narrow near-band gap emission at 2.97 eV with a linewidth of 40 meV. This emission has a typical PL decay time about 5 ns at 2 K within the PL contour. With increasing excitation intensity, an additional transition with longer decay time (about 200 ns) is enhanced at energy about 2.85 eV. The position of this line depends strongly on the excitation power. We explain the data in terms of a model, where the PL is a result of contribution from at least two nonequivalent QWs, which could be realized due to a potential gradient across the layers. (C) 2000 American Institute of Physics. [S0003- 6951(00)04337-0].
12.	Chang, KC, et al. (author) High-carbon concentrations at the silicon dioxide-silicon carbide interface identified by electron energy loss spectroscopy 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:14, s. 2186-2188 Journal article (peer-reviewed)abstract High carbon concentrations at distinct regions at thermally-grown SiO2/6H-SiC(0001) interfaces have been detected by electron energy loss spectroscopy (EELS). The thickness of these C-rich regions is estimated to be 10-15 Angstrom. The oxides were grown on n-type 6H-SiC at 1100 degrees C in a wet O-2 ambient for 4 h immediately after cleaning the substrates with the complete RCA process. In contrast, C-rich regions were not detected from EELS analyses of thermally grown SiO2/Si interfaces nor of chemical vapor deposition deposited SiO2/SiC interfaces. Silicon-rich layers within the SiC substrate adjacent to the thermally grown SiO2/SiC interface were also evident. The interface state density D-it in metal-oxide-SiC diodes (with thermally grown SiO2) was approximately 9x10(11) cm(-2) eV(-1) at E- E-v=2.0 eV, which compares well with reported values for SiC metal-oxide-semiconductor (MOS) diodes that have not received a postoxidation anneal. The C-rich regions and the change in SiC stoichiometry may be associated with the higher than desirable D-it's and the low channel mobilities in SiC-based MOS field effect transistors. (C) 2000 American Institute of Physics. [S0003-6951(00)01940-9].
13.	Mamor, M, et al. (author) High-energy He-ion irradiation-induced defects and their influence on the noise behavior of Pd/n-Si1-xGex Schottky junctions 2000 In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:25, s. 3750-3752 Journal article (peer-reviewed)abstract We report on the electrical properties of defects introduced by high-energy 5.4 MeV He ions in n-type strained n-SiGe and the impact of this irradiation on the noise properties of Pd/n-Si1-xGex Schottky barrier diodes (SBDs). From the deep level transient spectroscopy measurements, the main defects EA1 and EA2 are observed in both Si and Si0.96Ge0.04 and have energy levels at 0.24 and 0.44 eV, respectively, below the conduction band. EA1 and EA2 have been correlated with the V-V and the P-V pairs, respectively. For both defects EA1 and EA2, the energy level position is found to be the same for x = 0 and 0.04, indicating that such levels are pinned to the conduction band. Furthermore, the impact of the high-energy He-ion irradiation on the electrical noise properties of Pd/n-Si1-xGex SBDs is also studied. From the noise experimental data, the main noise source observed in these irradiated diodes was attributed to the generation-recombination noise inducing an abnormal peak in their noise spectra at around f(1) = 180 Hz. This peak is found to be independent of Ge concentration. (C) 2000 American Institute of Physics. [S0003-6951(00)02125-2].
14.	Abadei, S., et al. (author) DC field dependent properties of Na0.5 K0.5 NbO3/SiO2/Si structures at millimeter-wave frequencies 2001 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:13, s. 1900-1902 Journal article (peer-reviewed)abstract Dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Ω cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 μm. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices
15.	Abadei, S., et al. (author) DC field dependent properties of Na0.5K0.5NbO3/SiO2/Si structures at millimeter-wave frequencies 2001 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:13, s. 1900-1902 Journal article (peer-reviewed)abstract Dielectric properties of laser-ablated 0.5-mum-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Omega cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-mum-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 mum. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices.
16.	Aberg, D., et al. (author) Nitrogen deactivation by implantation-induced defects in 4H-SiC epitaxial layers 2001 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:19, s. 2908-2910 Journal article (peer-reviewed)abstract Ion implantation causes free charge carrier reduction due to damage in the crystalline structure. Here, nitrogen-doped 4H silicon carbide (n type) epitaxial layers have been investigated using low ion doses in order to resolve the initial stage of the charge carrier reduction. It was found that the reduction of free carriers per ion-induced vacancy increases with increasing nitrogen content. Nitrogen is suggested to be deactivated through reaction with migrating point defects, and silicon vacancies or alternatively interstitials are proposed as the most likely candidates.
17.	Aberg, I, et al. (author) Nanoscale tungsten aerosol particles embedded in GaAs 2002 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:16, s. 2976-2978 Journal article (peer-reviewed)abstract GaAs containing buried nanoscale tungsten particles has been characterized electrically. The particles were produced using a special aerosol process and were embedded in GaAs by epitaxial overgrowth. Two different particle sizes were investigated separately. When the particle concentration was increased, a conductance drop of about 500 times was observed. A simulation model, based on a random distribution of the particles, was developed and used to support our findings. The major advantage of our method is the simplicity and low processing cost.
18.	Ahuja, R., et al. (author) Electronic structure of Ti3SiC2 2000 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:16, s. 2226-2228 Journal article (peer-reviewed)
19.	Andersson, Peter, et al. (author) Switchable Optical Polarizer Based on Electrochromism in Stretch-Aligned Polyaniline 2003 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:7, s. 1307-1309 Journal article (peer-reviewed)abstract We report on the polarizing electrochromic (EC) effect of a conjugated polymer. This has been achieved in a planar flexible electrochemical device cell comprised of a patterned stretch-aligned thin film of polyaniline and an electrolyte, all made on a polyethylene foil substrate. The resulting device exhibits polarized absorption characteristics, of a dichroic ratio of 4, that can be controlled by the voltage applied. Also, thin flexible EC polarizers have been realized by combining two stretch-aligned polyaniline films with orthogonal stretching direction. In the resulting EC polarizer the orientation of the polarized absorption can be switched between two orthogonal directions, depending on the voltage applied.
20.	Aradi, B., et al. (author) Impurity-controlled dopant activation : Hydrogen-determined site selection of boron in silicon carbide 2001 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:17, s. 2746-2748 Journal article (peer-reviewed)abstract The geometry and formation energy of substitutional B and Al dopants as well as their complexes with hydrogen have been calculated in 4H-SiC using first-principles methods. Our results show that boron selecting the silicon site and, therefore, getting activated as a shallow acceptor depends on the presence of hydrogen which is promoted into the crystal by boron itself. Without hydrogen, boron would mostly be incorporated at the carbon site. Aluminum does not show this behavior: it always selects the silicon site and is incorporated independently of hydrogen. © 2001 American Institute of Physics.
21.	Arnaudov, B., et al. (author) Magnetic-field-induced localization of electrons in InGaN/GaN multiple quantum wells 2003 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:13, s. 2590-2592 Journal article (peer-reviewed)abstract A study was performed on the magnetic-field-induced localization of electrons in InGaN/GaN multiple quantum wells (MQW). A stepwise behavior of both the Hall coefficient and magnetoresistivity was observed. The peculiarities were explained by a magnetic-field-induced localization of electrons in a two-dimensional (2D) potential relief of the InGaN MQW.
22.	Björk, Mikael, et al. (author) Nanowire resonant tunneling diodes 2002 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:23, s. 4458-4460 Journal article (peer-reviewed)abstract Semiconductor heterostructures and their implementation into electronic and photonic devices have had tremendous impact on science and technology. In the development of quantum nanoelectronics, one-dimensional (1D) heterostructure devices are receiving a lot of interest. We report here functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires. The emitter, collector, and the central quantum dot are made from InAs and the barrier material from InP. Ideal resonant tunneling behavior, with peak-to-valley ratios of up to 50:1 and current densities of 1 nA/mum(2) was observed at low temperatures. (C) 2002 American Institute of Physics.
23.	Björk, Mikael, et al. (author) One-dimensional heterostructures in semiconductor nanowhiskers 2002 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:6, s. 1058-1060 Journal article (peer-reviewed)abstract We report on the growth of designed heterostructures placed within semiconductor nanowhiskers, exemplified by the InAs/InP material system. Based on transmission electron microscopy, we deduce the interfaces between InAs and InP to be atomically sharp. Electrical measurements of thermionic emission across an 80-nm-wide InP heterobarrier, positioned inside InAs whiskers 40 nm in diameter, yield a barrier height of 0.6 eV. On the basis of these results, we propose new branches of physics phenomena as well as new families of device structures that will now be possible to realize and explore.
24.	Bligaard, T., et al. (author) Pareto-optimal alloys 2003 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:22, s. 4527-4529 Journal article (peer-reviewed)abstract Large databases that can be used in the search for new materials with specific properties remain an elusive goal in materials science. The problem is complicated by the fact that the optimal material for a given application is usually a compromise between a number of materials properties and the cost. In this letter we present a database consisting of the lattice parameters, bulk moduli, and heats of formation for over 64 000 ordered metallic alloys, which has been established by direct first-principles density-functional-theory calculations. Furthermore, we use a concept from economic theory, the Pareto-optimal set, to determine optimal alloy solutions for the compromise between low compressibility, high stability, and cost.
25.	Blomqvist, Mats, et al. (author) High-performance epitaxial Na0.5K0.5NbO3 thin films by magnetron sputtering 2002 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:2, s. 337-339 Journal article (peer-reviewed)abstract Epitaxial Na0.5K0.5NbO3 (NKN) thin films have been grown on LaAlO3 substrates by rf magnetron sputtering of a stoichiometric, high-density, ceramic target. X-ray diffraction analysis showed c-axis oriented cube-on-cube growth. Micrometer size interdigital capacitor (IDC) structures were defined on the surface of the NKN film using photolithography. The electrical characterization at 1 MHz showed dissipation factor tan delta of 0.010, tunability 16.5% at 200 kV/cm and dielectric permittivity epsilon(r)=470. The frequency dispersion of epsilon(r) between 1 kHz and 1 MHz was 8.5% and the IDCs showed very good insulating properties with leakage current density on the order of 30 nA/cm(2) at 400 kV/cm. The polarization loop exhibits weak ferroelectric hysteresis with maximum polarization 23.5 muC/cm(2) at 600 kV/cm. These results are promising for tunable microwave devices based on rf sputtered NKN thin films.

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