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Sökning: L773:1862 6300 > (2015-2019)

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1.
  • Adamczyk, Krzysztof, et al. (författare)
  • Recombination Strength of Dislocations in High-Performance Multicrystalline/Quasi-Mono Hybrid Wafers During Solar Cell Processing
  • 2018
  • Ingår i: Physica Status Solidi (a) applications and materials science. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 215:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Wafers from a hybrid silicon ingot seeded in part for High Performance Multicrystalline, in part for a quasi-mono structure, are studied in terms of the effect of gettering and hydrogenation on their final Internal Quantum Efficiency.The wafers are thermally processed in different groups – gettered and hydrogenated. Afterwards, a low temperature heterojunction with intrinsic thin layer cell process is applied to minimize the impact of temperature. Such procedure made it possible to study the effect of different processing steps on dislocation clusters in the material using the Light Beam Induced Current technique with a high spatial resolution. The dislocation densities are measuredusing automatic image recognition on polished and etched samples. The dislocation recombination strengths are obtained by a correlation of the IQE with the dislocation density according to the Donolato model. Different clusters are compared after different process steps. The results show that for the middle of the ingot, the gettering step can increase the recombination strength of dislocations by one order of magnitude. A subsequent passivation with layers containing hydrogen can lead to a decrease in the recombination strength to levels lower than in ungettered samples.
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2.
  • Alnoor, Hatim, et al. (författare)
  • Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p-GaN light-emitting diode
  • 2017
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 214:1
  • Tidskriftsartikel (refereegranskat)abstract
    • As the low-temperature aqueous chemical synthesis (LT-ACS), holds great promises for the synthesis of one-dimensional (1D) ZnO nanostructure-based light-emitting diodes (LEDs) and hence require parameter tuning for optimal performance. N-ZnO nanorods (NRs)/p-GaN heterojunction LEDs have been synthesized by the LT-ACS using ZnO nanoparticle (NPs) seed layers prepared with different precursor solutions. The effect of these seed layers on the interface defect properties and emission intensity of the as-synthesized n-Zn/p-GaN heterojunction LEDs has been demonstrated by spatially resolved cathodoluminescence (CL) and electroluminescence (EL) measurements, respectively. A significant reduction of the interface defects in the n-ZnO NRs/p-GaN heterostructure synthesized from a seed layer prepared from zinc acetate (ZnAc) with a mixture of potassium hydroxide (KOH) and hexamethylenetetramine (HMTA) (donated as ZKH seed) compared with those prepared from ZnAc and KOH (donated as ZK seed) is observed as revealed by spatially resolved CL. Consequently, the LEDs based on n-ZnO NRs/p-GaN prepared from ZKH seed show an improvement in the yellow emission (approximate to 578nm) compared to that based on the ZK seed as deduced from the electroluminescence measurements. The improvement in the yellow EL emission on the ZKH LED probably attributed to the low presence of the non-radiative defect as deduced by light-output current (L-I) characteristics analysis.
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3.
  • Chulapakorn, Thawatchart, 1988-, et al. (författare)
  • Impact of H-uptake by forming gas annealing and ion implantation on photoluminescence of Si-nanoparticles
  • 2018
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 215:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon nanoparticles (SiNPs) are formed by implanting 70 keV Si+ into a SiO2-film and subsequent thermal annealing. SiNP samples are further annealed in forming gas. Another group of samples containing SiNP is implanted by 7.5 keV H+ and subsequently annealed in N2-atmosphere at 450 °C to reduce implantation damage. Nuclear reaction analysis (NRA) is employed to establish depth profiles of the H-concentration. Enhanced hydrogen concentrations are found close to the SiO2surface, with particularly high concentrations for the as-implanted SiO2. However, no detectable uptake of hydrogen is observed by NRA for samples treated by forming gas annealing (FGA). H-concentrations detected after H-implantation follow calculated implantation profiles. Photoluminescence (PL) spectroscopy is performed at room temperature to observe the SiNP PL. Whereas FGA is found to increase PL under certain conditions, i.e., annealing at high temperatures, increasing implantation fluence of H reduces the SiNP PL. Hydrogen implantation also introduces additional defect PL. After low-temperature annealing, the SiNP PL is found to improve, but the process is not found equivalently efficient as conventional FGA.
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4.
  • Diplas, Spyros, et al. (författare)
  • Materials for Energy Harvesting
  • 2018
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 215:17
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • n/a
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5.
  • Dong, Wenjing, et al. (författare)
  • Charge transport study of perovskite solar cells through constructing electron transport channels
  • 2017
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 214:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Perovskite solar cells (PSC) have attracted much attention in the recent years. It is important to understand their working principle in order to uncover the reasons behind their high efficiency. In this study, the carrier transport mechanism of PSC by controlling the structure of a scaffold is investigated. CeO2 is used as an electron blocking material in PSCs to study the electron transport behavior for the first time. The influence of light absorption can be excluded because CeO2 has a similar bandgap to TiO2. A variety of scaffolds are constructed using nano-TiO2 and CeO2. The results show that electrons can transport from light absober (perovskite) to FTO electrode (external circuit) through two kinds of channels. The energy band level, as well as the electronic conductivity of the scaffolds, is are key issues that affect electron transport. Although perovskites are able to transport both electrons and holes, it is still necessary to have effective electron transport channels (ETCs) between perovskite and external circuit for the sake of high efficiency. Electrochemical impedance spectroscopy analysis suggests that the lack of such channels will result in high recombination. The number of ETCs and effecient electron-hole separation are also proven to be important for cell performance.
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6.
  • Englund, Sven, et al. (författare)
  • Antimony-Doped Tin Oxide as Transparent Back Contact in Cu2ZnSnS4 Thin-Film Solar Cells
  • 2019
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 216:22
  • Tidskriftsartikel (refereegranskat)abstract
    • Antimony-doped tin oxide (Sn2O3:Sb, ATO) is investigated as a transparent back contact for Cu2ZnSnS4 (CZTS) thin-film solar cells. The stability of the ATO under different anneal conditions and the effect from ATO on CZTS absorber growth are studied. It is found that ATO directly exposed to sulfurizing anneal atmosphere reacts with S, but when covered by CZTS, it does not deteriorate when annealed at T < 550 degrees C. The electrical properties of ATO are even found to improve when CZTS is annealed at T = 534 degrees C. At T = 580 degrees C, it is found that ATO reacts with S and degrades. Analysis shows repeatedly that ATO affects the absorber growth as large amounts of Sn-S secondary compounds are found on the absorber surfaces. Time-resolved anneal series show that these compounds form early during anneal and evaporate with time to leave pinholes behind. Device performance can be improved by addition of Na prior to annealing. The best CZTS device on ATO back contact herein has an efficiency of 2.6%. As compared with a reference on a Mo back contact, a similar open-circuit voltage and short-circuit current density are achieved, but a lower fill factor is measured.
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7.
  • Englund, Sven, et al. (författare)
  • TiN Interlayers with Varied Thickness in Cu2ZnSnS(e)(4) Thin Film Solar Cells : Effect on Na Diffusion, Back Contact Stability, and Performance
  • 2018
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 215:23
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, interlayers with varied thickness of TiN between Cu2ZnSnS(e)(4) (CZTS(e)) absorbers and Mo on soda-lime glass substrates are investigated for CZTS(e) thin film solar cells. Na diffusion is analyzed using Secondary Ion Mass Spectrometry and it is found that the use of thick TiN interlayers facilitates Na diffusion into the absorbers. The CZTS(e)/TiN/Mo interfaces are scrutinized using Transmission Electron Microscopy (TEM) Electron Energy Loss Spectroscopy (EELS). It is found that diffusion of chalcogens present in the precursor occurs through openings, resulting from surface roughness in the Mo, in the otherwise chemically stable TiN interlayers, forming point contacts of MoS(e)(2). It is further established that both chalcogens and Mo diffuse along the TiN interlayer grain boundaries. Solar cell performance for sulfur-annealed samples improved with increased thickness of TiN, and with a 200 nm TiN interlayer, the solar cell performance is comparable to a typical Mo reference. Pure TiN bulk contacts are investigated and shown to work, but the performance is still inferior to the TiN interlayer back contacts. The use of thick TiN interlayers offers a pathway to achieve high efficiency CZTS(e) solar cells on highly inert back contacts.
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8.
  • Giannazzo, F., et al. (författare)
  • Graphene integration with nitride semiconductors for high power and high frequency electronics
  • 2017
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 214:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Group III nitride semiconductors (III-N), including GaN, AlN, InN, and their alloys, are currently the materials of choice for many applications in optoelectronics (light-emitting diodes, laser diodes), and high-power and high-frequency transistors. Due to its attractive electrical, optical, mechanical, and thermal properties, graphene (Gr) integration with III-N technology has been considered in the last few years, in order to address some of the major issues which still limit the performances of GaN-based devices. To date, most of the studies have been focused on the use of Gr as transparent conductive electrode (TCE) to improve current spreading from top electrodes and light extraction in GaN-LEDs. This paper will review recent works evaluating the benefits of Gr integration with III-N for high power and high frequency electronics. From the materials side, recent progresses in the growth of high quality GaN layers on Gr templates and in the deposition of Gr on III-N substrates and templates will be presented. From the applications side, strategies to use Gr for thermal management in high-power AlGaN/GaN transistors will be discussed. Finally, recent proposals of implementing new ultra-high-frequency (THz) transistors, such as the Gr base hot electron transistor (GBHET), by Gr integration with III-N will be highlighted. (C) 2016 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim
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11.
  • Keller, Jan, et al. (författare)
  • Atomic layer deposition of In2O3 transparent conductive oxide layers for application in Cu(In,Ga)Se2 solar cells with different buffer layers
  • 2016
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 213:6, s. 1541-1552
  • Tidskriftsartikel (refereegranskat)abstract
    • This contribution presents the development of atomic layer deposited (ALD) In2O3 films for utilization as transparent conductive oxide (TCO) layers in Cu(In,Ga)Se2 (CIGSe) solar cells. The effects of ALD process parameters on the morphology and growth of In2O3 are studied and related to the electrical and optical properties of the films. Maintaining similar resistivity values compared to commonly used ZnO:Al (AZO) TCOs (ρ = (5–7) × 10−4 Ωcm), a superior mobility of μ ≈ 110 cm2/Vs could be achieved (more than five times higher than a ZnO:Al reference), which results in a significantly reduced parasitic optical absorption in the infrared region. Application of the optimized In2O3 layers in CIGSe solar cells with varying buffer layers (CdS and Zn1–xSnxOy (ZTO)) leads to a distinct improvement in short circuit current density Jsc in both cases. While for solar cells containing the ZTO/In2O3 window structure, a drop in open-circuit voltage Voc and a deterioration under illumination is observed, the TCO exchange (from AZO to In2O3) on CdS buffer layers results in an increase in Voc without detectable light bias degradation. The efficiency η of the best corresponding solar cells could be improved by about 1% absolute.
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12.
  • Keller, Jan, et al. (författare)
  • Effect of Cu content on post‐sulfurization of Cu(In,Ga)Se2 films and corresponding solar cell performance
  • 2019
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 216:20
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, the effect of the initial copper content of co‐evaporated Cu(In1−x,Gax)Se2 (CIGS) absorber films on the impact of a post‐annealing step in elemental sulfur atmosphere is studied. The Cu concentration is varied over a wide range ([Cu]/[III] = CGI = 0.57–1.23), allowing to identify composition‐dependent trends in phase formation, chemical rearrangements, and solar cell performance after sulfurization. For all samples, a ternary CuInS2 layer forms at the surface. In addition, sulfur 1) is incorporated in randomly distributed CuIn(S,Se)2 mixed crystals underneath CuInS2; 2) diffuses into multidimensional defects (e.g., dislocations and grain boundaries); and 3) is bound in Na–In–S surface plates. It is found that Cu‐poor absorber composition (CGI ≤ 0.82) favors CuInS2 growth as compared with close‐stoichiometric CIGS films, driven by a faster diffusion of Cu toward the surface. For Cu‐rich absorbers (CGI > 1), Se—S exchange is significantly accelerated, presumably by the presence of Cu2−xSe phases reacting to Cu2−xS and eventually catalyzing CuInS2 formation. Finally, open‐circuit voltage (VOC), fill factor (FF), and efficiency (η) of corresponding solar cells increase after sulfurization with increasing CGI until stoichiometry is reached. The result is explained by a mitigated Cu depletion of the absorber bulk after sulfurization for close‐stoichiometric CIGS.
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13.
  • Khan, Azam, et al. (författare)
  • Analysis of direct and converse piezoelectric responses from zinc oxide nanowires grown on a conductive fabric
  • 2015
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 212:3, s. 579-584
  • Tidskriftsartikel (refereegranskat)abstract
    • Single crystalline hexagonal wurtzite zinc oxide nanowires were grown on conductive commercial textile fabric as piezoelectric material. Aqueous chemical growth (ACG) method was used for the synthesis of ZnO nanowires. Field emission surface scanning electron microscopy and X-ray diffraction techniques were used for surface and structural analysis of grown nanowires. The mechanical and piezoelectric properties of the nanowires were investigated by nanoindantation. Piezoelectric potentials up to 0.013 V were measured in response to direct applied loads in the range 0 - 11 mN. Also, a DC voltage was applied for measurement of converse piezoelectric response under a low constant applied force (~5 μN) and the piezoelectric coefficient was found to be 33.2 pm/V. This study performed on commercial conductive textile demonstrates the feasibility to fabricate wearable nanogenerator clothing.
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14.
  • Larsen, Jes K, et al. (författare)
  • Potential of CuS cap to prevent decomposition of Cu2ZnSnS4 during annealing
  • 2015
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 212:12, s. 2843-2849
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the challenges associated with processing of Cu2ZnSnS4 (CZTS) is the thermal decomposition reaction that causes loss of S and SnS from the absorber surface. To reduce the decomposition a sufficiently high SnS and S partial pressure must be supplied during annealing. The absorber surface can alternatively be protected with a thin cap. Aiming to obtain a more flexible process, CZTS precursors were capped with a thin CuS layer before annealing. The cap was subsequently removed with a KCN etch before device finishing. It was found that the cap coverage decreased during annealing, exposing a part of the absorber surface. At the same time, the initially Cu poor absorber took up Cu from the cap, ending up with a stoichiometric Cu content. Devices made from capped precursors or precursors annealed without sulfur had poor device characteristics. An increased doping density of almost one order of magnitude could be the reason for the very poor performance. CuS is therefore not a suitable cap material for CZTS. Other cap materials could be investigated to protect the CZTS absorber surface during annealing.
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15.
  • Lenz, Thomas, et al. (författare)
  • Microstructured organic ferroelectric thin film capacitors by solution micromolding
  • 2015
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 212:10, s. 2124-2132
  • Tidskriftsartikel (refereegranskat)abstract
    • Ferroelectric nanostructures offer a promising route for novel integrated electronic devices such as non-volatile memories. Here we present a facile fabrication route for ferroelectric capacitors comprising a linear array of the ferroelectric random copolymer of vinylidenefluoride and trifluoroethylene (P(VDF-TrFE)) interdigitated with the electrically insulating polymer polyvinyl alcohol (PVA). Micrometer size line gratings of both polymers were fabricated over large area by solution micromolding, a soft lithography method. The binary linear arrays were realized by backfilling with the second polymer. We investigated in detail the device physics of the patterned capacitors. The electrical equivalent circuit is a linear capacitor of PVA in parallel with a ferroelectric capacitor of P(VDF-TrFE). The binary arrays are electrically characterized by both conventional Sawyer-Tower and shunt measurements. The dependence of the remanent polarization on the array topography is explained by numerical simulation of the electric field distribution.
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16.
  • Lopez-Lorente, Angela, et al. (författare)
  • Mid-infrared thin-film diamond waveguides combined with tunable quantum cascade lasers for analyzing the secondary structure of proteins
  • 2016
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 213:8, s. 2117-2123
  • Tidskriftsartikel (refereegranskat)abstract
    • Diamond has excellent optical properties including broadband transmissivity, low self-absorption, and a high refractive index, which have prompted its use for optical sensing applications. Thin-film diamond strip waveguides (DSWGs) combined with tunable quantum cascade lasers (tQCLs) providing an emission wavelength range of 5.78-6.35 mu m (1735-1570 cm(-1)) have been used to obtain mid-infrared (MIR) spectra of proteins, thereby enabling the analysis of their secondary structure via the amide I band. Three different proteins were analyzed, namely bovine serum albumin (BSA), myoglobin, and gamma-globulin. The secondary structure of BSA and myoglobin has a major contribution of a-helices, whereas gamma-globulins are rich in beta-sheet structures, which is reflected in the amide I band. Acomparison of the spectra obtained via the combination of the tQCL and DSWG with spectra obtained using conventional Fourier transform infrared (FTIR) spectroscopy and a commercial diamond attenuated total reflection (ATR) element has been performed. It is shown that the main features evident in FTIR-ATR spectra are also obtained using tQCL-DSWG sensors.
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17.
  • Messina, Luca, et al. (författare)
  • An object kinetic Monte Carlo model for the microstructure evolution of neutron-irradiated reactor pressure vessel steels
  • 2016
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 213:11, s. 2974-2980
  • Tidskriftsartikel (refereegranskat)abstract
    • This work presents a full object kinetic Monte Carlo framework for the simulation of the microstructure evolution of reactor pressure vessel (RPV) steels. The model pursues a "gray-alloy" approach, where the effect of solute atoms is seen exclusively as a reduction of the mobility of defect clusters. The same set of parameters yields a satisfactory evolution for two different types of alloys, in very different irradiation conditions: an Fe-C-MnNi model alloy (high flux) and a high-Mn, high-Ni RPV steel (low flux). A satisfactory match with the experimental characterizations is obtained only if assuming a substantial immobilization of vacancy clusters due to solute atoms, which is here verified by means of independent atomistic kinetic Monte Carlo simulations. The microstructure evolution of the two alloys is strongly affected by the dose rate; a predominance of single defects and small defect clusters is observed at low dose rates, whereas larger defect clusters appear at high dose rates. In both cases, the predicted density of interstitial loops matches the experimental solute-cluster density, suggesting that the MnNi-rich nanofeatures might form as a consequence of solute enrichment on immobilized small interstitial loops, which are invisible to the electron microscope.
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18.
  • Nour, Eiman, et al. (författare)
  • Low frequency accelerator sensor based on piezoelectric ZnO nanorods grown by low temperature scalable process
  • 2016
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-Blackwell. - 1862-6300 .- 1862-6319. ; 213:9, s. 2503-2508
  • Tidskriftsartikel (refereegranskat)abstract
    • Piezoelectric vertically aligned zinc oxide (ZnO) nanorods (NRs) were grown by low temperature aqueous chemical approach and successfully used as a low frequency self-powered accelerator detector system. The nanogenerator (NG) device was tested under the influence of low frequency vibrations, different load masses, and finger prints pressure. The experimental results show relatively high sensitivity to frequencies as low as 5 Hz. This energy conversion device has produced a maximum output voltage of about 0.3 and 1.4 V under a frequency of 41 Hz and a mass of 1000 g, respectively. The fabricated NG can be used as an accelerator sensor with a good performance in the range from about 0.67 to 5.5 m s−2 with a sensitivity of 0.045 V s2 m−1. Furthermore, it has been demonstrated that the NG is able to harvest energy under finger-print scanning. The result from the finger-print pressure was consistent with the masses testing results. This energy-harvesting technology also provides a simple and cost-effective platform to capture low-frequency mechanical energy, i.e., body movements, and other applications like developing a sensitive finger print camera, etc.
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19.
  • Omanakuttan, Giriprasanth, et al. (författare)
  • Epitaxial lateral overgrowth of GaxIn1-xP toward direct GaxIn1-xP/Si heterojunction
  • 2017
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 214:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The growth of GaInP by hydride vapor phase epitaxy (HVPE) was studied on planar GaAs, patterned GaAs for epitaxial lateral overgrowth (ELOG), and InP/Si seed templates for corrugated epitaxial lateral overgrowth (CELOG). First results on the growth of direct GaInP/Si heterojunction by CELOG is presented. The properties of GaxIn(1-x)P layer and their dependence on the process parameters were investigated by X-ray diffraction, including reciprocal lattice mapping (XRD-RLM), scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDS), photoluminescence (PL), and Raman spectroscopy. The fluctuation of Ga composition in the GaxIn(1-x)P layer was observed on planar substrate, and the strain caused by the composition variation is retained until relaxation occurs. Fully relaxed GaInP layers were obtained by ELOG and CELOG. Raman spectroscopy reveals that there is a certain amount of ordering in all of the layers except those grown at high temperatures. Orientation dependent Ga incorporation in the CELOG, but not in the ELOG GaxIn(1-x)P layer, and Si incorporation in the vicinity of direct GaxIn(1-x)P/Si heterojunction from CELOG are observed in the SEM-EDS analyses. The high optical quality of direct GaInP/Si heterojunction was observed by cross-sectional micro-PL mapping and the defect reduction effect of CELOG was revealed by high PL intensity in GaInP above Si.
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20.
  • Pevere, Federico, et al. (författare)
  • Effect of X-ray irradiation on the blinking of single silicon nanocrystals
  • 2015
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 212:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Photoluminescence (PL) intermittency (blinking) observed for single silicon nanocrystals (Si-NCs) embedded in oxide is usually attributed to trapping/de-trapping of carriers in the vicinity of the NC. Following this model, we propose that blinking could be modified by introducing new trap sites, for example, via X-rays. In this work, we present a study of the effect of X-ray irradiation (up to 65 kGy in SiO) on the blinking of single Si-NCs embedded in oxide nanowalls. We show that the luminescence characteristics, such as spectrum and life-time, are unaffected by X-rays. However, substantial changes in ON-state PL intensity, switching frequency, and duty cycle emerge from the blinking traces, while the ON- and OFF- time distributions remain of mono-exponential character. Although we do not observe a clear monotonic dependence of the blinking parameters on the absorbed dose, our study suggests that, in the future, Si-NCs could be blinking-engineered via X-ray irradiation.
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21.
  • Reuterskiold Hedlund, Carl, et al. (författare)
  • Trench-Confined InP-Based Epitaxial Regrowth Using Metal-Organic Vapor-Phase Epitaxy
  • 2018
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 215:8
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, an area-selective metal-organic vapor-phase epitaxy (MOVPE) for trench-confined InP-based epitaxial regrowth in-between arrayed rectangular-shaped device elements is reported. Test structures are fabricated to investigate the influence of MOVPE growth and other processing parameters on regrowth control, doping incorporation, and morphology. For correctly chosen crystallographic mesa orientation and mask geometry, good control of growth selectivity, layer morphology, and doping concentration can be achieved, although with an enhanced and non-constant growth rate. This is discussed in terms of orientation-dependent growth rate and loading effects. In addition, a selective etch and regrowth approach which allows for the processing of field-effect transistors of significance for spatial light modulators with trench-integrated driver electronics is successfully implemented.
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22.
  • Reuterskiöld-Hedlund, Carl, et al. (författare)
  • Buried-Tunnel Junction Current Injection for InP-Based Nanomembrane Photonic Crystal Surface Emitting Lasers on Silicon
  • 2019
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 217:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, the design, metal-organic vapor-phase epitaxial growth, fabrication, and characterization of buried-tunnel junction (BTJ) current injection structures for InP/Si hybrid nanomembrane photonic crystal surface emitting lasers (PCSELs) are reported. Corresponding BTJ-light-emitting diodes on InP substrate show low series resistance and uniform carrier injection over square-shaped device areas with side length ranging from 15 up to 250 mu m, whereas BTJ-PCSEL structures with similar current injection configuration fabricated on photonic-crystal silicon-on-insulator substrate using transfer print technology show significant linewidth narrowing at low current density.
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23.
  • Saini, Nishant, et al. (författare)
  • Germanium Incorporation in Cu2ZnSnS4 and Formation of a Sn–Ge Gradient
  • 2019
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 216:22
  • Tidskriftsartikel (refereegranskat)abstract
    • Alloying of Cu2ZnSnS4 (CZTS) with Ge can potentially promote grain growth and suppress the formation of Sn‐related defects. Herein, a two‐step fabrication route based on compound co‐sputtering and sulfurization at a high temperature is used to prepare Ge‐incorporated CZTS (Cu2ZnGexSn1 − xS4 [CZGTS]). For Cu2ZnGeS4 (CZGS), films deposited using elemental Ge and binary GeS targets are compared. The recrystallization is shown to be promoted for the absorbers deposited using Ge target, possibly due to lower sulfur content in the precursor suppressing the formation of wurtzite‐like phases during sputtering. The grain growth and crystallinity in CZGTS are slightly improved for x = 0.2 but not for higher concentration of the incorporated Ge. Owing to the composition‐dependent electronic properties, compositionally graded CZGTS films may be beneficial for reducing recombination towards the back contact. Hence, herein, the successful formation of a steep concentration gradient with Ge and Sn is demonstrated by the deposition of a CZGS/CZTS precursor stack followed by sulfurization with varying time periods.
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24.
  • Santos, Paulo, et al. (författare)
  • Theory of a carbon-oxygen-hydrogen recombination center in n-type Si
  • 2017
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 214:7
  • Tidskriftsartikel (refereegranskat)abstract
    • We have recently found that in-diffusion of hydrogen into n-type Si crystals containing oxygen and carbon impurities can result in the formation of powerful recombination centers (M. Vaqueiro-Contreras et al., to appear in PSS RRL). Here, we describe a combination of first-principles calculations and electrical measurements to investigate the composition, structure, electrical activity and recombination mechanism of a carbon-oxygen-hydrogen complex (COH) in Si. We found a defect comprising a carbon-oxygen complex connected to an H atom whose location depends on the charge state of the complex, and showing a calculated acceptor level at Ev+0.3eV, a few meV away from the observations. Bistable carbon-oxygen-hydrogen complex in silicon. Carbon, oxygen, hydrogen, and silicon atoms are shown in gray, red, black, and white, respectively
  •  
25.
  • Song, Yang, 1981-, et al. (författare)
  • A Theoretical Study of Dye Molecules Adsorbed onto Diamond (111) Surfaces
  • 2016
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 213:8, s. 2105-2111
  • Tidskriftsartikel (refereegranskat)abstract
    • The combinations of different dye molecules adsorbed on 100% H-terminated B-doped diamond (111) surfaces, have been carefully simulated by using DFT under periodic boundary conditions. The dye molecules include C20H13NO3S4, C35H37NO2S3, C34H38OS2, C32H36OS2, and C31H35S3Br. The functional group within these dyes, behaves as an electron acceptor during the sunlight harvesting process. By comparing the upper valence band edge of the diamond surface with the HOMO and LUMO levels of the dyes in an energy diagram, a suitable scheme for a p-type dye sensitized solar cell was constructed. These functionalities were further confirmed by the observation of a partial degree of electron transfer from the diamond surface to the dye molecules. The combination of spectra for the dye molecules showed a wide absorption range from 200nm to 620nm. The effect of B doping on the binding of the dye molecules have furthermore been investigated. Shorter diamond//dye bonds are well correlated with large electron bond populations, and a larger degree of electron transfer. The former is regarded to be a meassure of covalency, and the latter a meassure of ionicity, in the interfacial bond. 
  •  
26.
  • Tingberg, Tobias, 1984, et al. (författare)
  • Step-flow growth of GaN(0001) on 4H-SiC(0001) by plasma-assisted molecular beam epitaxy
  • 2016
  • Ingår i: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 213:9, s. 2498-2502
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on step-flow growth of GaN(0001) on 4H-SiC(0001) substrates by plasma-assisted molecular beam epitaxy. The GaN layers were deposited directly on the substrate without using a buffer layer. A growth temperature of 900 degrees C and above resulted in an atomically flat surface morphology with locally straight steps indicating step-flow growth. The step height was 0.21 nm corresponding to one-half unit cell. The terrace width was 97 nm and the root-mean-square roughness was 0.06 nm. Samples grown below 900 degrees C exhibited a surface morphology consisting of spiraling terraces forming hexagonal hillocks. The full-width at half-maximum for X-ray rocking-curves recorded across the (0002) and (10 (1) over bar5) reflections was as narrow as 62 and 587 arcsec, respectively. We show that the high growth temperature in conjunction with Ga adlayers on the growth front provides a path for achieving step-flow growth of GaN by MBE.
  •  
27.
  • Trompoukis, C., et al. (författare)
  • Photonic nanostructures for advanced light trapping in thin crystalline silicon solar cells
  • 2015
  • Ingår i: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 212:1, s. 140-155
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the fabrication, integration, and simulation, both optical and optoelectrical, of two-dimensional photonic nanostructures for advanced light trapping in thin crystalline silicon (c-Si) solar cells. The photonic nanostructures are fabricated by the combination of various lithography (nanoimprint, laser interference, and hole mask colloidal) and etching (dry plasma and wet chemical) techniques. The nanopatterning possibilities thus range from periodic to random corrugations and from inverted nanopyramids to high aspect ratio profiles. Optically, the nanopatterning results in better performance than the standard pyramid texturing, showing a more robust behavior with respect to light incidence angle. Electrically, wet etching results in higher minority carrier lifetimes compared to dry etching. From the integration of the photonic nanostructures into a micron-thin c-Si solar cell certain factors limiting the efficiencies are identified. More precisely: (a) the parasitic absorption is limiting the short circuit current, (b) the conformality of thin-film coatings on the nanopatterned surface is limiting the fill factor, and (c) the material damage from dry etching is limiting the open circuit voltage. From optical simulations, the optimal pattern parameters are identified. From optoelectrical simulations, cell design considerations are discussed, suggesting to position the junction on the opposite side of the nanopattern.
  •  
28.
  • Tsigkourakos, Menelaos, et al. (författare)
  • Suppression of boron incorporation at the early growth phases of boron-doped diamond thin films
  • 2015
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 212:11, s. 2595-2599
  • Tidskriftsartikel (refereegranskat)abstract
    • The presence of O during the chemical vapour deposition (CVD) of B-doped diamond results in the suppression of B incorporation into the diamond film. In this study, we demonstrate that the amount of residual O within the chamber is higher at the beginning of the diamond growth due to the O-contaminated chamber walls, and is decreased after a certain time period. This leads to a gradual increase of the B incorporation by more than one order of magnitude during the early growth phases of nanocrystalline diamond (NCD). We further show that this suppression of B incorporation at the early growth phases of B-doped diamond is influenced by the growth rate of the film. This is attributed to the constant time period whereby most of the residual O interacts with the B-precursors in the gas phase by forming stable B-O species, which are flushed out from the chamber exhaust. Furthermore, the constant B profile of an NCD film grown in a loadlock hot-filament CVD (HFCVD) system reveals that the amount of residual O is constant and minimal during the growth process. Therefore, our work proves that the use of a loadlock overcomes the B-suppression problem at the early growth phases of diamond, making it the optimal solution for the growth of highly conductive thin diamond films.
  •  
29.
  • Zamulko, Sergiy, et al. (författare)
  • Optical Properties of Cu2ZnSn(SxSe1-x)(4) by First-Principles Calculations
  • 2018
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 215:17
  • Tidskriftsartikel (refereegranskat)abstract
    • Structural, electronic, and optical properties of Cu2ZnSn(SxSe1-x)(4) semiconductors are studied theoretically for different concentration of S and Se anions. The optical properties are calculated at three levels of theory, in the generalized gradient approximation (GGA), meta-GGA, and with a hybrid functional. The GGA and meta-GGA calculations are corrected with an on-site Coulomb U-d term. Lattice constants, dielectric constants, and band-gaps are found to vary almost linearly with the concentration of S. The authors also show that a dense sampling of the Brillouin zone is required to accurately account for the shape of the dielectric function, which is hard to attain with hybrid functionals. This issue is resolved with a recently developed kp based interpolation scheme, which allows us to compare results of the hybrid functional calculations on an equal footing with the GGA and meta-GGA results. We find that the hybrid functionals provide the overall best agreement with the experimental dielectric function.
  •  
30.
  • Zukauskaite, Agne, et al. (författare)
  • Nanoprobe Mechanical and Piezoelectric Characterization of ScxAl1-xN(0001) Thin Films
  • 2015
  • Ingår i: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 212:3, s. 666-673
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanoindentation with in-situ electrical characterization was used to characterize piezoelectric scandium aluminum nitride (ScxAl1-xN) thin films with Sc contents up to x=0.3. The films were prepared by reactive magnetron sputtering using Al2O3 substrates with TiN seed layer/bottom electrodes at a substrate temperature of 400 °C. X-ray diffraction shows c-axis oriented wurtzite ScxAl1-xN, where the crystal quality decreases with increasing x. Piezoresponse force microscopy in mapping mode shows a single piezoelectric polarization phase in all samples. The hardness and decreases from 17 GPa in AlN to 11 GPa in Sc0.3Al0.7N, while reduced elastic modulus decreases from 265 GPa to 224 GPa, respectively. Both direct and converse piezoelectric measurements are demonstrated by first applying the load and generating the voltage and later by applying the voltage and measuring film displacement using a conductive boron doped nanoindenter tip. The Sc0.2Al0.8N films exhibit an increase in generated voltage by 15% in comparison to AlN and a correspondingly larger displacement upon applied voltage, comparable to results obtained by double beam interferometry and piezoresponse force microscopy. 
  •  
31.
  • Ginley, D., et al. (författare)
  • Transparent Oxides and Related Materials for Electronics and Optics : Phys. Status Solidi A
  • 2019
  • Ingår i: physica status solidi (a). - Weinheim : Wiley. - 1862-6300.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The International Symposium on Transparent Oxide Thin Films for Electronics and Optics (TOEO) has been held every two years since 1997. The 10th TOEO conference (TOEO‐10), whose name was changed to The International Symposium on Transparent Oxide and Related Materials for Electronics and Optics so as to include recent related material from TOEO‐8, was held July 3–5, 2017, at International Conference Center, Waseda University, Tokyo, Japan. This conference was very successful and included 105 participants. The TOEO sessions had one special panel discussion on “Energy, the global challenge”, 22 invited talks, 6 contributed oral papers, and 34 poster presentations.We are pleased to publish this special issue of Physica Status Solidi (a). The highest‐quality papers were selected through on‐site review at the conference and by the standard peer‐review process following the criteria of the journal. We expect that this volume will promote the research on transparent oxide materials.The organizers thank Japan Society for the Promotion of Science, the 166th Committee, for continued support.
  •  
32.
  • Ren, Yi, et al. (författare)
  • Influence of the Cu2ZnSnS4 absorberthickness on thin film solar cells
  • 2015
  • Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 212:12, s. 2889-2896
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, we investigate the influence of absorber thickness on Cu2ZnSnS4 (CZTS) solar cells, ranging from 500 to 2000 nm, with nearly constant metallic composition. Despite the observed ZnS and SnS phases on the surface and backside of all absorber films, scanning electron microscopy, Raman scattering, and X-ray diffraction show no large variations in material quality for the different thicknesses. The open-circuit voltage (V-oc), short-circuit current and overall power conversion efficiency of the fabricated devices show an initial improvement as the absorber thickness increases but saturate when the thickness exceeds 750 nm. External quantum efficiency (EQE) measurements suggest that the current is mainly limited by collection losses. This can result from non-optimal bulk quality of the CZTS absorber (including the presence of secondary phases), which is apparently further reduced for the thinnest devices. The observed saturation of V-oc agrees with the expected influence from strong interface recombination. Finally, an effective collection depth of 750-1000 nm for the minority carriers generated in the absorber can be estimated from EQE, indicating that the proper absorber thickness for our device process is approximately 1000 nm. Performance could be improved for thicker films, if the collection depth can be increased.
  •  
33.
  • Zeller, Patrick, et al. (författare)
  • Scanning Photoelectron Spectro-Microscopy : A Modern Tool for the Study of Materials at the Nanoscale
  • 2018
  • Ingår i: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6300. ; 215:19
  • Tidskriftsartikel (refereegranskat)abstract
    • The advanced properties of modern materials originate from their nanoscale size and shape and from chemical modifications or doping. Special techniques that can measure the chemical state in the nanoscale are required for exploration and understanding the properties of these materials. While X-ray photoelectron spectroscopy (XPS) can access the necessary chemical information, conventional setups have no spatial resolution. The scanning photoelectron microscope (SPEM) takes in advent the third generation synchrotron radiation facilities and uses a zone plate (ZP) focusing optics that allows spatially resolved XPS measurements in the submicron scale. Several recent examples of investigations of chemically modified or doped nanomaterials are given. The modification of suspended and supported graphene with nitrogen and fluorine is presented as well as the doping dependent position of the Fermi-level in single GsAs nanowires and the Mott–Hubbard transition in Cr-doped vanadium oxide. These examples show several peculiar SPEM abilities like a high surface and chemical sensitivity and a submicron spatial resolution proving the capability and importance of this technique to study materials at the nanoscale.
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