PL Data Research Articles

Microscale Spatially Resolved Characterization of Highly Doped Regions in Laser-Fired Contacts for High-Efficiency Crystalline Si Solar Cells

Laser-fired contact (LFC) processes have emerged as a promising approach to create rear local electric contacts in p-type crystalline silicon solar cells. Although this approach has been successfully applied in devices showing efficiencies above 20%, there is still a lack of knowledge about some specific features of LFCs at the submicron level. In this study, we used micro-Raman and microphotoluminescence (PL) spectroscopies to carry out a highresolution spatially resolved characterization of LFCs processed in Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -passivated c-Si wafers. Relevant information concerning features such as local doping distribution and crystalline fraction of the laser-processed region has been obtained. In particular, interesting qualitative and quantitative variations concerning the doping profile have been observed between LFCs processed at different laser powers. Finally, conductive-atomic force microscopy measurements have allowed to identify the existence of highly conductive zones inside the LFCs greatly correlated with highly doped regions revealed by Raman and PL data. This study gives a detailed insight about the LFCs characteristics at the submicron level and their possible influence on the performance of final devices.

Quantum size effects on the optical properties of nc-Si QDs embedded in an a-SiOx matrix synthesized by spontaneous plasma processing.

Quantum confinement effects on optical transitions in ensembles of nc-Si QDs in an a-SiOx matrix has become evident by simultaneously considering the dielectric function dispersions obtained by optical modeling with spectroscopic ellipsometry, the absorption edge, and the photoluminescence peak. Diminution of the peak amplitude in the ε2-spectra for reducing the diameter of nc-Si QDs could arise due to the disappearance of excitonic effects in the E1 transition, while the peak broadening indicates an amplification of disorder in Si QDs. An energy blue shift happens to take place in an analogous fashion for all the characteristic parameters, upon decreasing the size of the nc-Si QDs for diameters in the range 6.5 < d < 2.0 nm. The band gap widening with the reduction of QD size is well supported by the first-principles calculations based on quantum confinement, while studies on the Stokes shift in the optical gap from the PL data could provide an understanding of the imperfect passivation of the surface defects on tiny nc-Si QDs. Low dimensional nc-Si QDs (∼2 nm in diameter) assembled in a large density (∼2.3 × 10(12) cm(-2)) embedded in an a-SiOx matrix synthesized by spontaneous and low-temperature (300 °C) RF plasma processing, compatible to CMOS technology, are highly conducive for device applications. Systematic changes in composition and characteristics, including the thickness, of the individual sub-layers of the nc-Si QD thin films can be comprehensively pursued through a nondestructive process by ellipsometric simulation which could, thereby, enormously contribute to the precise optimization of the deposition parameters suitable for specific device fabrication e.g., all-silicon tandem solar cells and light emitting diodes, using silicon nanotechnology.

(Keynote) Epitaxy-Based Strain-Engineering Methods for Advanced Devices

Progress in epitaxial methodology as well as in nanotechnology opened new routes to custom design novel device structures harboring highly mismatched layers as well as materials far beyond the solubility limit. In this paper we discuss III/V nanostructures as well as SiGeSn alloys grown on Si(100). Taking GaAs/InAs core shell nanowires as an example, the possibility to control the crystal structure enables to fabricate advanced radial/axial heterostructures by phase selective epitaxy. Controlling (GaIn)As/(GaIn)Sb core shell nanowires offer broken and staggered bandgap alignments for the design of advanced tunnel FETs. Finally (Si)GeSn alloys of extraordinary structural quality with Sn concentration up to 14% were deposited by reactive gas source epitaxy. PL and absorption data give evidence for a fundamental direct band gap in these materials. The potential of these materials for ultra-low power electronic devices as well as for optoelectronics is demonstrated.

Enhanced Solubilization of Carbon Nanotubes in Aqueous Suspensions of Anionic–Nonionic Surfactant Mixtures

Single-walled carbon nanotubes (SWCNTs) suspensions in aqueous solutions of sodium dodecyl sulfate (SDS) and saturated fatty acids (Cn) are studied. The quality of the dispersions is analyzed by photoluminescence spectroscopy (PL) as a function of the Cn chain length. Resonant Raman scattering (RRS) measurements and molecular dynamics (MD) simulations were also carried out in order to study the effect of the surrounding medium on SWCNTs properties in suspensions. Both PL and RRS data indicate an increased individualization of SWCNTs in the dispersions for Cn’s having an alkyl chain longer than SDS. MD simulations showed the formation of mixed Cn-SDS aggregates around a nanotube in water and a Cn binding energy to the nanotube wall that increases linearly with chain length. The enhanced solubilization of SWCNTs is thus interpreted in terms of the reduced electrostatic repulsion within the surfactant aggregates and the increased binding energy to the nanotube wall. Powders prepared by the evaporation of dis...

New Optical Properties of Porosity Layer Controlled by Laser-Induced Etching

Three different power densities and fixed irradiation times have been used to prepare porous silicon using laserinduced etching process to control the size and shape of nanostructure. There are new optical properties of porous silicon. Scanning electron microscopy was used to study surface morphology after the etching process. Porous silicon was characterized using spectroscopic studies. There is shift in Raman peak position as a result of the increase of power densities. The photoluminescence spectra (PL) tend to blue shift in peak position due to etching conditions. Raman and PL data were explained using appropriate dimensional confinement of size and size distributions of nanocrystallites. There has been an agreement between the results of Raman and PL spectroscopic studies of the PS samples. Keywords: Nanostructure, porous silicon, spectroscopic, raman, PL, LIE.

Investigation of the optical and electrical properties of p-type porous GaAs structure

Porous GaAs layers have been formed by electrochemical anodic etching of (100) heavily doped p-type GaAs substrate in a HF:C2H5OH solution. The surface morphology of porous GaAs has been studied using atomic force microscopy (AFM).Nano-structural nature of the porous layer has been demonstrated by X-ray diffraction analysis (XRD) and confirmed by AFM. An estimation of the main size of the GaAs crystallites obtained from effective mass theory and based on PL data was close to the lowest value obtained from the AFM results. The porous p-GaAs samples are characterised by spectroscopic ellipsometry and modulation spectroscopy techniques. The objective of this study is to determine the porosity, refractive index, and thickness. The porosity of GaAs determined by atomic force microscopy confirmed by the value obtained from the spectroscopic ellipsometry. In fact the current–voltage I(V) characteristics of metal–semiconductor Au/p-GaAs are investigated and compared with Au/p-porous GaAs structures. From the forward bias I(V) characteristics of these devices, the main electrical parameters such as ideality factor, barrier height, and series resistance have been determined.

Energy transfer between Tb3+ and Eu3+ in co-doped Y2O3 nanocrystals prepared by Pechini method

Tb3+ and Eu3+ co-doped Y2O3 nanoparticles with a volume-weighted average size of about 30 nm were synthesized via simple Pechini-type sol–gel process. The growth of monocrystalline nanoparticles is investigated via XRD and TEM analysis. The study of energy transfer between Tb3+ and Eu3+ ions was carried out by means of PL, PLE, and photoluminescence decay analyses. The energy transfer from Tb3+ to Eu3+ is efficient and we show how a resonant type via a dipole–dipole interaction is the most probable mechanism. We compared the energy-transfer efficiencies calculated from the intensities and from the lifetimes of \({}^5\hbox{D}_4 \longrightarrow ^7\hbox{F}_5\) transition of Tb, showing the presence of two populations of Tb, with different local surroundings, in the matrix. Furthermore, the critical distance between Tb3+ and Eu3+ ions has been calculated by means of different theories, from a new probabilistic approach based on the discretization of the theory of Chandrasekhar about the distribution of the nearest neighbors in a random distribution of particles, and from the PL data, suggesting a value of about 7 A.

Low Temperature Synthesis of CdSe Nanocrystal Quantum Dots using Paraffin Oil

We report a simple and rapid route for synthesis of CdSe quantum dots at low temperature of 150°C by using the paraffin oil as a solvent in place of the conventional trioctylphosphine and trioctylphosphine oxide. The CdSe QDs were synthesized as a function of the growth temperature. UV-vis and PL data show a narrow emission peak at 552 nm with absorption peak of 533 nm, implying a uniform size distribution. The CdSe QDs reveal large blue-shifts in both UV-vis and PL data under the low temperature conditions, due to the quantum confinement effect depending on the smaller particle size.

Intrinsic increase in lymphangion muscle contractility in response to elevated afterload

Collecting lymphatic vessels share functional and biochemical characteristics with cardiac muscle; thus, we hypothesized that the lymphatic vessel pump would exhibit behavior analogous to homeometric regulation of the cardiac pump in its adaptation to elevated afterload, i.e., an increase in contractility. Single lymphangions containing two valves were isolated from the rat mesenteric microcirculation, cannulated, and pressurized for in vitro study. Pressures at either end of the lymphangion [input pressure (P(in)), preload; output pressure (P(out)), afterload] were set by a servo controller. Intralymphangion pressure (P(L)) was measured using a servo-null micropipette while internal diameter and valve positions were monitored using video methods. The responses to step- and ramp-wise increases in P(out) (at low, constant P(in)) were determined. P(L )and diameter data recorded during single contraction cycles were used to generate pressure-volume (P-V) relationships for the subsequent analysis of lymphangion pump behavior. Ramp-wise P(out) elevation led to progressive vessel constriction, a rise in end-systolic diameter, and an increase in contraction frequency. Step-wise P(out) elevation produced initial vessel distention followed by time-dependent declines in end-systolic and end-diastolic diameters. Significantly, a 30% leftward shift in the end-systolic P-V relationship accompanied an 84% increase in dP/dt after a step increase in P(out), consistent with an increase in contractility. Calculations of stroke work from the P-V loop area revealed that robust pumps produced net positive work to expel fluid throughout the entire afterload range, whereas weaker pumps exhibited progressively more negative work as gradual afterload elevation led to pump failure. We conclude that lymphatic muscle adapts to output pressure elevation with an intrinsic increase in contractility and that this compensatory mechanism facilitates the maintenance of lymph pump output in the face of edemagenic and/or gravitational loads.

Effect of Annealing Atmosphere on the Optical and Magnetic Properties of Cr Doped ZnO Samples

We synthesize two Zn0 90Cr0 10O samples using solid state reaction method; one annealed in Air and another annealed in Ar/H2 atmosphere. We compared the optical and magnetic properties of these samples synthesized in different annealing atmospheres. XRD studies of the samples reveal shift in the ZnO peaks due to Cr-doping suggesting incorporation of Cr at Zn sites in ZnO. EDS give different values of Cr concentration for Zn0 90Cr0 10O samples annealed in air and Ar/H2 atmosphere, i.e., 7.4 at% in air and 12.03 at% in Ar/H2. UV-VIS-NIR spectroscopy showed that the reflectance intensity decreases with increase in Cr concentration. PL data suggests the presence of defects in the Cr-doped ZnO samples in addition to the presence of NBE band. The magnetic measurements show paramagnetic behavior for air annealed Zn0 90Cr0 10O sample whereas Ar/H2 annealed sample shows RTFM. The observed RTFM in the present case may be attributed to the Cr concentration and the oxygen vacancies produced on annealing the sample in Ar/H2.

Targeted profiling of atherogenic phospholipids in human plasma and lipoproteins of hyperlipidemic patients using MALDI-QIT-TOF-MS/MS

ObjectivesPhospholipids (PLs) are increasingly recognized as key molecules with potential diagnostic value in acute inflammation, CVD and atherosclerosis. We introduce a pioneer mass spectrometry (MS)-based approach aiming to investigate the relationship of specific plasma PL-subsets with atherogenic blood parameters in young patients with familial hyperlipidemia representing high-CVD-risk groups. MethodsPlasma of carefully phenotyped FH and FCH patients as well as normolipidemic subjects (age 13 ± 5 years, n = 20) was used. Clinical parameters were assessed using standard laboratory techniques and lipids were subjected to a direct targeted monitoring using LC-ESI-SRM- and MALDI-QIT-TOF-MS/MS, respectively. Statistical analysis was performed to evaluate correlations between PL data and the clinical parameters. ResultsMost characteristically significant differences of SM/PC and PC/LPC ratios and positive correlations between SM vs. LDL-C (r = 0.946; p = 0.004) and LPC vs. VLDL-C (r = 0.669; p = 0.218) were observed in FH in contrast to the other study groups. OxPC levels were found in the range of ∼2–20 μmol/L with predominance of short-chain aldehydic species (e.g. SOVPC). A positive correlation of OxPCs with IMT (r = 0.952; p = 0.052) and HDL-C (r = 0.893; p = 0.016) but negative correlation with OxLDL (r = −0.910; p = 0.096) was observed. ConclusionsOur study was a first attempt to use a MALDI-QIT-TOF-MS/MS based clinical lipidomics approach to investigate atherogenic dyslipidemia in young patients with familial hyperlipidemia. This technique represents a promising platform for clinical screening of lipid biomarkers in the future.

Time and Temperature Dependence of CdS Nanoparticles Grown in a Polystyrene Matrix

Luminescent CdS nanocrystals embedded in a polystyrene matrix were successfully prepared. The in situ growth of CdS QDs was realized by thermal treatment of Cd bis(thiolate)/polymer foil at different times and temperatures (240°C and 300°C) of annealing, in order to evaluate their influence on the quantum dots growth process. As a general trend, the increasing of time and temperature of annealing induces a rise of the CdS nanocrystals size into the polymeric matrix. The size distribution, morphology, and structure of the CdS nanoparticles were analysed with HRTEM and XRD experiments. UV‐Vis and PL data are strongly size‐dependent and were used to investigate the particles′ growth process, too. The CdS nanoparticles behavior in solution indicated a general trend of QDs to aggregation. This predisposition was clearly displayed by DLS measurements.

Growth, structural and optical properties of GaN/AlN and GaN/GaInN nanowire heterostructures

Abstract After discussing the GaN NW nucleation issue, we will present the structural properties of axial and radial (i.e. core/shell) GaN/AlN NW heterostructures and adress the issue of critical thickness during the growth of such heterostructures. Next, we will present the growth of InGaN NWs on a GaN NW base. It will be shown that the morphology and structural properties of the InGaN NW sections depend on the In content: for high In content a flat top is observed and plastic relaxation is occuring, with mismatch dislocations formed at the InGaN/GaN interface. By contrast, for In content below 25% InGaN NWs exhibit a pencil-like shape assigned to a purely elastic strain relaxation process, without formation of dislocations. Such a strain relaxation process was found to be associated with the spontaneous formation of an InGaN/GaN core-shell heterostructure. As concerns optical properties, it will be shown that the purely elastic relaxation process is associated with a marked In clustering. As a consequence, for samples with a 17% nominal In content, data were found to exhibit a S-shape characteristic of localization, with a minimum around 110K. By contrast, for a 40% In content PL data suggest that localization is much weaker. Finally, a growth model of InGaN/GaN heterostructures will be proposed.

Influence of Catalyses on the Preparation of YVO4:Eu3+ Phosphors by the Sol–gel Methodology

YVO(4):Eu(3+) phosphors have been prepared by the hydrolytic sol-gel methodology, with and without alkaline catalyst. The solid powder was obtained by reaction between yttrium III chloride and vanadium alkoxides; the europium III chloride was used as structural probe. The powder was treated at 100, 400, 600, or 800 °C for 4 h. The samples were characterized by X-ray diffraction, thermal analysis, and photoluminescence. The XRD patterns revealed YVO(4) crystalline phase formation for the sample prepared without the catalyst and heat-treated at 600 °C and for the sample prepared in the presence of ammonium as catalyst and heat-treated at 100 °C. The average nanosized crystallites were estimated by the Scherrer equation. The sample which was produced via alkaline catalysis underwent weight loss in two stages, at 100 and 400 °C, whereas the sample obtained without catalyst presented four stages of weight loss, at 150, 250, 400, and 650 °C. The excitation spectra of the samples treated at different temperatures displayed the charge transfer band (CTB) at 320 nm. PL data of all the samples revealed the characteristic transition bands arising from the (5)D(0) → (5)F(J) (J = 0, 1, 2, 3, and 4) manifolds under maximum excitation at 320, 394, and 466 nm in all cases. The (5)D(0) → (7)F(2) transition often dominates the emission spectra, indicating that the Eu(3+) ion occupies a site without inversion center. The long lifetime suggests that the matrix can be applied as phosphors. In conclusion, the sol-gel methodology is a very efficient approach for the production of phosphors at low temperature.

Synthesis and photoluminescence of Y,Eu co-doped ZnO red phosphor

A red emitting ZnO·Y 2O 3:Eu phosphor has been prepared using pyrolysis technique at temperatures ≤1000 °C. When NH 4Cl was used as an ingredient, its luminescence efficiency was quite high indicating that Cl − ions act as charge compensators since the introduction of Y 3+ and Eu 3+ cations in ZnO lattice demands the introduction of equal amount of excess anions. However, Na + or Li + quenches the luminescence efficiency of ZnO·Y 2O 3:Eu. Due to ZnO host absorption, the excitation peaks of ZnO·Y 2O 3:Eu phosphor near 260 nm and 394 nm are suppressed while the one at 468 nm is intense. This red emitting phosphor may find applications when monochromatic excitation such as lasers are involved. XRD data of (Zn 0.93Y 0.07)O z :Eu 3+,Cl − shows the presence of the ZnO phase as well as the Y 2O 3 phase. It shows that Y 2O 3 forms a sublattice within ZnO host. This is supported by the PL data of (Zn 0.93Y 0.07)O z :Eu 3+,Cl − which showed no significant change in the PL efficiency with increase in ZnO molar concentration.

Enhanced photoluminescence around 1540 nm from erbium doped silicon coimplanted with hydrogen and silver

This work reports on an approach based on coimplantation of hydrogen and silver for improving luminescence around 1540 nm from erbium doped silicon. As a result of H induced nanocavities and their gettering of implanted Ag ions, Ag nanostructures are formed in Si doped with erbium and oxygen. The presence of such nanostructures can lead to an enhancement of more than a factor of 2 in Er photoluminescence, compared to the control sample. In addition, analysis of PL data suggests that both the Er excitation cross section and the Er optical activation are increased by the formation of Ag nanostructures. We discuss possible mechanisms for these findings.

Nanostructured GaN on silicon fabricated by electrochemical and laser-induced etching

Nanostructured GaN layers have been fabricated by electrochemical and laser-induced etching (LIE) processes based on n-type GaN thin films grown on the Si (111) substrate with AlN buffer layers. The effect of varying current and laser power density on the morphology of the GaN layers is investigated. The etched samples exhibited a dramatic increase in photoluminescence intensity as compared to the as grown samples. The average diameter of the GaN crystallites was about 7–10 nm, as determined from the PL data The Raman spectra also displayed stronger intensity peaks, which were shifted and broadened as a function of etching parameters. A strong band at 522 cm − 1 is from the Si (111) substrate, and a small band at 301 cm − 1 , due to the acoustic phonons of Si. Two Raman active optical phonons are assigned h-GaN at 139 cm − 1 and 568 cm − 1 due to E2 (low) and E2 (high) respectively.

Dimethylzinc adduct chemistry revisited: MOCVD of vertically aligned ZnO nanowires using the dimethylzinc 1,4-dioxane adduct

The dimethylzinc adduct [Me 2Zn(1,4-dioxane)] has been used for the growth of vertically aligned ZnO nanowires by liquid injection MOCVD. The ZnO nanowires were deposited at temperatures of 450 and 500 °C on Si(1 1 1) and F-doped SnO 2/glass substrates and XRD data showed that the ZnO nanowires were deposited in the wurtzitic phase. Room temperature PL data for the nanowires showed that they are of high crystalline quality with intense near band-edge emission at 3.28 eV and a very low intensity of defect-related green luminescence at 2.42 eV. Single crystal XRD data showed that the [Me 2Zn(1,4-dioxane)] adduct is polymeric with repeating [Me 2Zn] units bridged by monodentate 1,4-dioxane ligands.

Formation and photoluminescence of Si quantum dots in SiO 2/Si 3N 4 hybrid matrix for all-Si tandem solar cells

In this work, Si quantum dots in SiO 2/Si 3N 4 hybrid matrix on quartz substrates were synthesized by magnetron sputtering of alternating silicon rich oxide and Si 3N 4 layers followed by different post-deposition anneals. XRD results indicate that the average dimension of the Si nanocrystals varies from 1.6 to 5.2 nm. The size and crystallization of the Si nanocrystals are dependent on a number of factors, including the annealing method, the SRO thickness and the Si 3N 4 barrier thickness, as evidenced in XRD and Raman measurements. In particular, thicker Si 3N 4 barrier layers seem to be able to suppress the growth of Si nanocrystals more effectively. PL measurements suggest the apparent bandgap of the samples investigated in this work is in the range 1.12–1.67 eV, which demonstrates the effect of quantum confinement. More interestingly, analysis of the PL data using the modified EMA equations clearly suggests that the PL peak energy not only depends on the size of the nanocrystals but also gets affected by other details in nanocrystal growth. A tentative core–shell model is constructed to illustrate our explanation. These findings offer a preliminary understanding of the nanocrystal growth and radiative recombination processes in this newly synthesized material for photovoltaic applications.

Relationship between crystal morphology and photoluminescence in polynanocrystalline lead sulfide thin films

Thin films of lead sulfide (PbS) nanoparticles were grown on corning glass and Si(1 0 0) substrates by polyethylene glycol-assisted chemical bath deposition (CBD) method. This paper compares the morphology and the luminescence properties (PL) of the deposited thin films in the presence (or absence) of PEG300 and investigates the effect of deposition temperatures. Surface morphology and photoluminescence properties of samples were analyzed. The PL data show a blue-shift from the normal emission at ∼2900 nm in PbS bulk to ∼360 nm in nanoparticles of PbS thin films. Furthermore, the PL emission of the films obtained without the addition of PEG300 (type 1) was slightly shifted from that of the films obtained in presence of PEG300 (type 2) from ∼360 to ∼470 nm. The blue-shifting of the emission wavelengths from 2900 to ∼360 or 470 nm is attributed to quantum confinement of charge carriers in the restricted volume of nanoparticles, while the shift between the two types of PbS nanoparticles thin films is speculated to be due to an increase in the defect concentration. The blue-shift increased with increase of the deposition temperature, which suggests that there has been a relative depletion in particle sizes during the CBD of the films at higher temperatures. The PbS nanocrystalline thin films obtained in the presence of PEG300 at 60 °C exhibit a high blue luminescence.