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GeSn alloys are a promising emerging complementary metal–oxide–semiconductor compatible technology for applications in photonics and electronics. However, the unavoidable intrinsic compressive strain introduced during epitaxial growth has prevented researchers from pushing the performance of GeSn devices to the limit and realizing real-world applications. In this paper, we present a straightforward geometric strain-inversion technique that harnesses the harmful compressive strain to achieve beneficial tensile strain in GeSn nanowires, drastically increasing the directness of the band structure. We achieve ∼2.67% uniaxial tensile strain in ∼120 nm wide nanowires, surpassing other values reported thus far. Unique pseudo-superlattices comprising of indirect and direct bandgap GeSn are demonstrated in a single material only by applying a periodic tensile strain. Improved directness in tensile-strained GeSn significantly enhances the photoluminescence by a factor of ∼2.5. This work represents a way to develop scalable band-engineered GeSn nanowire devices with lithographic design flexibility. This technique can be potentially applied to any layer with an intrinsic compressive strain, creating opportunities for unique tensile strained materials with diverse electronic and photonic applications. [ABSTRACT FROM AUTHOR]

The control of the local strain profile in 2D materials offers an invaluable tool for tailoring the electronic and photonic properties of solid-state devices. In this paper, we demonstrate a local engineering of the exciton photoluminescence (PL) energy of monolayer tungsten disulfide (WS2) by means of strain. We apply a local uniaxial stress to WS2 by exploiting electron-beam patterned and actuated polymeric micrometric artificial muscles (MAMs), which we implement onto monolithic synthetic WS2/graphene heterostructures. We show that MAMs are able to induce an in-plane stress to the top WS2 layer of the van der Waals heterostructure and that the latter can slide on the graphene underneath with negligible friction. As a proof of concept for the local strain-induced PL shift experiments, we exploit a two-MAM configuration in order to apply uniaxial tensile stress on well-defined micrometric regions of WS2. Remarkably, our architecture does not require the adoption of fragile suspended microstructures. We observe a spatial modulation of the excitonic PL energy of the WS2 monolayers under stress, which agrees with the expected strain profile and attains a maximum redshift of about 40 meV at the maximum strain intensity point. After the actuation, a time-dependent PL blueshift is observed in agreement with the viscoelastic properties of the polymeric MAMs. Our approach enables inducing local and arbitrary deformation profiles and circumvents some key limitations and technical challenges of alternative strain engineering methods requiring the 2D material transfer and production of suspended membranes. [ABSTRACT FROM AUTHOR]

Point defects in semiconductors are relevant for use in quantum technologies as room temperature qubits and single photon emitters. Among suggested defects for these applications are the negatively charged silicon vacancy and the neutral divacancy in SiC. The possible nonequivalent configurations of these defects have been identified in 4H-SiC, but for 6H-SiC, the work is still in progress. In this paper, we identify the different configurations of the silicon vacancy and the divacancy defects to each of the V1-V3 and the QL1-QL6 color centers in 6H-SiC, respectively. We accomplish this by comparing the results from ab initio calculations with experimental measurements for the zero-phonon line, hyperfine tensor, and zero-field splitting. [ABSTRACT FROM AUTHOR]

Organic solar cells have attractive potential for space applications as they have very high specific power (power generated per weight) and ultra-high flexibility (to reduce stowed volume). However, one critical issue is whether they are stable under the harsh space environment, particularly their stability under high energy, high flux, electron and proton bombardment. In this paper, the stability of benchmark organic photovoltaic layers under proton bombardment (150 keV with a fluence of 1 × 1012/cm2) and electron bombardment (1 MeV with a fluence of 1 × 1013/cm2) under vacuum is investigated. Raman spectroscopy, photoluminescence spectroscopy, and optical reflectance spectroscopy are applied to study their chemical/structural, photo-chemical/morphological, and optical stability after the bombardments. The results show that all the benchmark organic photovoltaic films are stable under the radiation, implying that organic solar cells could be feasible for space applications. [ABSTRACT FROM AUTHOR]

We present a method for three-dimensional intrinsic defect imaging in zinc oxide (ZnO) by spectrally resolved two-photon fluorescence microscopy, based on the previously presented method of observing a photoluminescence distribution in wide-gap semiconductor crystals [Noor et al., Appl. Phys. Lett. 92(16), 161106 (2008)]. A tightly focused light beam radiated by a titanium-sapphire laser is used to obtain a two-photon excitation of selected area of the ZnO sample. Photoluminescence intensity of a specific spectral range is then selected by optical band pass filters and measured by a photo-multiplier tube. Reconstruction of the specimen image is done by scanning the volume of interest by a piezoelectric positioning stage and measuring the spectrally resolved photoluminescence intensity at each point. The method has been proved to be effective at locating intrinsic defects of the ZnO crystalline structure in the volume of the crystal. The method was compared with other defect imaging and 3D imaging techniques like scanning tunneling microscopy and confocal microscopy. In both cases, our method shows superior penetration abilities and, as the only method, allows location of the defects of the chosen type in 3D. In this paper, we present the results of oxygen vacancies and zinc antisites imaging in ZnO nanorods. [ABSTRACT FROM AUTHOR]

The migration of vacancies in diamond is of considerable fundamental interest and has been widely studied previously, while the involvement of self-interstitials in diamond is less common except through centers such as 3H, 515.8 nm, 533.5 nm, and 580 nm. In this paper, the annealing and lateral migration of some interstitial-related centers in type IIa diamond are investigated by low temperature photoluminescence (PL) microscopy, and the distributions of interstitial- and vacancy-related centers are also clearly presented and discussed. [ABSTRACT FROM AUTHOR]

This paper reports a temperature-dependent (10-280 K) photoluminescence (PL) study of belowbandgap electron-hole recombinations and anomalous negative thermal quenching of PL intensity in InP1-xBix (x=0.019 and 0.023). Four PL features are well resolved by curve-fitting of the PL spectra, of which the energies exhibit different temperature dependence. The integral intensities of the two high-energy features diminish monotonically as temperature rises up, while those of the two low-energy features decrease below but increase anomalously above 180 K. A phenomenological model is established that the residual electrons in the final state of the PL transition transfer into nonradiative state via thermal hopping, and the thermal hopping produces in parallel holes in the final state and hence enhances the radiative recombination significantly. A reasonable interpretation of the PL processes in InPBi is achieved, and the activation energies of the PL quenching and thermal hopping are deduced. [ABSTRACT FROM AUTHOR]

The bulk and surface recombination determine the electrical performance of many semiconductor devices. Yet, the experimental determination and separation of both surface and bulk recombination rate remains challenging. This paper presents the measurement and separation of the bulk and surface recombination in silicon by means of time resolved photoluminescence spectroscopy. The high temporal resolution of the applied time correlated single photon counting technique is exploited to access the photoluminescence response of a silicon sample upon pulsed excitation in the nanosecond to millisecond regime on a sub-cm2 area. A rigorous data fitting algorithm based on two dimensional numeric simulations of the induced charge carrier dynamics is applied to extract all information on bulk and surface recombination properties from the recorded photoluminescence transients. Using different samples with symmetric as well as asymmetric surface recombination properties, we demonstrate the capabilities of the proposed contactless and nondestructive technique, which may be applicable to silicon based mono- or multi-junction devices. [ABSTRACT FROM AUTHOR]

This paper presents the heteroepitaxial growth of ultrawide bandgap β-Ga2O3 thin films on c-plane sapphire substrates by low pressure chemical vapor deposition. N-type conductivity in silicon (Si)-doped β-Ga2O3 films grown on sapphire substrate is demonstrated. The thin films were synthesized using high purity metallic gallium (Ga) and oxygen (O2) as precursors. The morphology, crystal quality, and properties of the as-grown thin films were characterized and analyzed by field emission scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, photoluminescence and optical, photoluminescence excitation spectroscopy, and temperature dependent van der Pauw/Hall measurement. The optical bandgap is ∼4.76 eV, and room temperature electron mobility of 42.35 cm²/V s was measured for a Si-doped heteroepitaxial β-Ga2O3 film with a doping concentration of 1.32×1018 cm-3. [ABSTRACT FROM AUTHOR]

Lanthanide ions possess fascinating optical properties and have received great attention due to their widespread technological applications. However, enhancing and in-situ tuning the photoluminescence is still a challenging subject. The paper shows that in 0-3 type lead-free ferroelectric composites constructed by ZnO and 1.0mol.% Er-doped 0.94Bi0.5Na0.5TiO3-0.06BaTiO3, the up-conversion photoluminescence of Er3+ ion can be unusually increased by 4.5 times after introducing 40mol.% ZnO, and then further enhanced by 1.2 times with electrical poling. The mechanism is attributed to the ZnO-mediated energy transfer and the electric field-induced phase transition. The composites also show excellent electrical properties and improved temperature stability. These results not only provide a hybrid method to significantly enhance and in-situ tune the photoluminescence but also are helpful for developing multifunctional materials with excellent optical and electrical properties simultaneously. [ABSTRACT FROM AUTHOR]

Lanthanide ions possess fascinating optical properties and have received great attention due to their widespread technological applications. However, enhancing and in-situ tuning the photoluminescence is still a challenging subject. The paper shows that in 0-3 type lead-free ferroelectric composites constructed by ZnO and 1.0 mol. % Er-doped 0.94Bi0.5Na0.5TiO3-0.06BaTiO3, the up-conversion photoluminescence of Er3+ ion can be unusually increased by 4.5 times after introducing 40 mol. % ZnO, and then further enhanced by 1.2 times with electrical poling. The mechanism is attributed to the ZnO-mediated energy transfer and the electric field-induced phase transition. The composites also show excellent electrical properties and improved temperature stability. These results not only provide a hybrid method to significantly enhance and in-situ tune the photoluminescence but also are helpful for developing multifunctional materials with excellent optical and electrical properties simultaneously. [ABSTRACT FROM AUTHOR]

In this paper, we study a family of solid-state, organic semiconductors for visible light communications. The star-shaped molecules have a boron-dipyrromethene (BODIPY) core with a range of side arm lengths which control the photophysical properties. The molecules emit red light with photoluminescence quantum yields ranging from 22% to 56%. Thin films of the most promising BODIPY molecules were used as a red colour converter for visible light communications. The film enabled colour conversion with a modulation bandwidth of 73MHz, which is 16 times higher than that of a typical phosphor used in LED lighting systems. A data rate of 370 Mbit/s was demonstrated using On-Off keying modulation in a free space link with a distance of ∼15 cm. [ABSTRACT FROM AUTHOR]

In this paper, the temperature dependent lasing characteristics of solution-processed organic-inorganic halide perovskite CH3NH3PbI3 films have been demonstrated. The lasing temperature can be sustained up to a near room temperature at 260 K. Via the temperature dependent photoluminescence (PL) measurements, an emerged phase-transition band can be observed, ascribing to the crystalline structures changed from the orthorhombic to tetragonal phase states in the perovskites as a function of a gradual increase in the ambient temperature. The optical characteristics of the PL emission peaks and the anomalous shifts of the peak intensities are highly correspondent with the phase states in perovskites at different temperatures, showing a low-threshold lasing behavior at the phase transition. The laser cavities may be formed under multiple random scattering provided by the polycrystalline grain boundary and/or phase separation upon the phase transition. Since the threshold gain is potentially high in the random cavities, the large material gain exhibited by the solution-processed perovskite would be very promising in making practical laser devices. [ABSTRACT FROM AUTHOR]

In this paper, we report on the effects of including Si-doped (In)GaN prelayers on the low temperature optical properties of a blue-light emitting InGaN/GaN single quantum well. We observed a large blue shift of the photoluminescence peak emission energy and significant increases in the radiative recombination rate for the quantum well structures that incorporated Si-doped prelayers. Simulations of the variation of the conduction and valence band energies show that a strong modification of the band profile occurs for the quantum wells on Si-doped prelayers due to an increase in strength of the surface polarization field. The enhanced surface polarization field opposes the built-in field across the quantum well and thus reduces this built-in electric field. This reduction of the electric field across the quantum well reduces the Quantum Confined Stark Effect and is responsible for the observed blue shift and the change in the recombination dynamics. [ABSTRACT FROM AUTHOR]

In this paper, we present the fabrication of dilute nitride semiconductor GaAs1-xNx by nitrogen-ion-implantation and flash lamp annealing (FLA). N was implanted into the GaAs wafers with atomic concentration of about ximp1=0.38% and ximp2=0.76%. The GaAs1-xNx layer is regrown on GaAs during FLA treatment in a solid phase epitaxy process. Room temperature near band-edge photoluminescence (PL) has been observed from the FLA treated GaAs1-xNx samples. According to the redshift of the near band-edge PL peak, up to 80% and 44% of the implanted N atoms have been incorporated into the lattice by FLA for ximp1=0.38% and ximp2=0.76%, respectively. Our investigation shows that ion implantation followed by ultrashort flash lamp treatment, which allows for large scale production, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the thermal carrier process in bimodal-sized In(Ga)As/GaAs quantum dots (QDs) via temperature dependent photoluminescence (PL). The PL intensity ratio of low energy modal to high energy modal is observed to be temperature sensitive and show different trends for QDs with weak and strong lateral coupling strength, i.e., rise and drop with increasing temperature, respectively. The experimental results are explained by two competing processes: (i) carrier thermal escape from each modal to wetting layer state and (ii) direct carrier coupling between two modals. An improved carrier rate equation model is developed to further demonstrate the importance of process ii in strong lateral coupled QDs system. [ABSTRACT FROM AUTHOR]

In this paper, we report the fabrication and characterization of Schottky rectifying junctions between semiconducting, modified single-layer graphene and a metal. The pristine, semimetallic behavior of graphene is altered by controlled exposure to an oxygen plasma, resulting in the opening of an optical band gap as shown by photoluminescence spectroscopy. The occurrence of a Schottky barrier between semiconducting graphene and metals with different work functions (Al, Cr, Pd, and Yb) is investigated by electrically characterizing the as-fabricated junctions. The rectifying properties of our Schottky diodes show the potential of semiconducting, modified graphene as building block of elementary logic circuits. [ABSTRACT FROM AUTHOR]

In this paper, we report our study on gold (Au) films with different thicknesses deposited on single layer graphene (SLG) as surface enhanced Raman scattering (SERS) substrates for the characterization of rhodamine (R6G) molecules. We find that an Au film with a thickness of ∼7 nm deposited on SLG is an ideal substrate for SERS, giving the strongest Raman signals for the molecules and the weakest photoluminescence (PL) background. While Au films effectively enhance both the Raman and PL signals of molecules, SLG effectively quenches the PL signals from the Au film and molecules. The former is due to the electromagnetic mechanism involved while the latter is due to the strong resonance energy transfer from Au to SLG. Hence, the combination of Au films and SLG can be widely used in the characterization of low concentration molecules with relatively weak Raman signals. [ABSTRACT FROM AUTHOR]

This paper presents a study on the emission efficiency enhancement of InAsSb nanostructures using a carrier blocking layer. InP is proposed to serve as the carrier blocking layer to suppress the thermal escape of carriers in InAsSb nanostructures and significantly enhance their emission efficiency at high temperature (good photoluminescence signal even at 330 K). However, this leads to a blueshift in their emission wavelength due to the significantly increased quantum confinement of the nanostructures. By inserting a thin InGaAs layer between InP blocking layer and InAsSb nanostructures, longer emission wavelength can be maintained. This provides an approach to achieve InAsSb nanostructures with both good high-temperature optical characteristics and long emission wavelength, which is very useful for fabricating mid-infrared emitters operating at room temperature. [ABSTRACT FROM AUTHOR]

A GaSb/GaAs quantum-dot light-emitting diode (QD LED) with a single GaSb QD layer is investigated in this paper. The room-temperature photoluminescence peak blueshift with increasing excitation power densities suggests a type-II alignment of the GaSb/GaAs heterostructures. Significant electroluminescence (EL) is observed for the device under forward biases, which suggests that pronounced dipole transitions occur at the GaSb/GaAs interfaces. With increasing forward biases, the observed EL peak blueshift confirms that the origin of luminescence is from the type-II GaSb/GaAs QD structures. A model is established to explain the operation mechanisms of the type-II QD LED. [ABSTRACT FROM AUTHOR]

The traceability of polyethylcyanoacrylate nanoparticles transported through human skin is studied in this paper. Photoluminescence is used to find the precise diffusion path of polyethylcyanoacrylate nanoparticles through the skin stratum corneum (SC). Reproducible data were obtained, and the nanoparticles’ distribution in each layer of the SC is presented. We contribute to the basic knowledge of these phenomena as a stationary stochastic process using a one-dimensional linear chain model with the left end open and the right end closed. Possible applications are in the field of pharmaceutical technology, especially concerning drug transport through the skin by nanoparticle carriers. [ABSTRACT FROM AUTHOR]

In this paper we study the influence of progressing oxidation on the photoluminescence spectra of small silicon nanocrystals (SiNCs). H-terminated SiNCs exhibit only a fast approximately nanosecond photoluminescence component at ∼525 nm, quenched and redshifted to ∼550 nm by progressing oxidation. At the same time a new approximately microsecond photoluminescence component appears, intensity of which progressively increases and its peak position redshifts continuously from 575 up to 660 nm. We interpret our observations in terms of the quasidirect core electron-hole pair recombination quenched by the ultrafast trapping into the oxygen-related surface/interface states, forming within the band gap due to oxidation. [ABSTRACT FROM AUTHOR]

The surface plasmon-enhanced spontaneous emission based on an organic light-emitting device is reported in this paper. For surface plasmon localization, silver nanoparticles were thermally deposited in a high vacuum on cathode that had a 1-nm-thick LiF spacer. Since plasmons provide a strong oscillator decay channel, time-resolved photoluminescence (PL) results displayed a 1.75-fold increased emission rate, and continuous wave PL results showed a twofold enhanced intensity. In addition, LiF film/Ag cluster/LiF film structure resolved the carrier injection problem between the cathode and the organic layer. Thus, the suggested design may follow plasmonic applications for a wider organic optoelectronics. [ABSTRACT FROM AUTHOR]

In this paper, we had quantitatively investigated the photoluminescence of organic emitter on a Si substrate with periodically corrugated metal thin film experimentally and theoretically. Due to the plasmonic coupling by the metal gratings, 4.3 times and 1.7 times enhancements in optical intensities were observed at specified and full viewing angles at certain wavelengths, respectively. Good agreement of angular-frequency versus in-plane wavevector (ω-k) curves between experiments and calculations were obtained when varying organic materials, metal materials, and grating pitches. Two different metal materials were used, which show slight shift in ω-k curves due to the high sensitivity of the surface plasmon to the relative permittivity. [ABSTRACT FROM AUTHOR]

In this paper, a highly conductive and strongly absorptive organic thin film by doping Ag into N,N′-bis (2,6-di-isopropylphenyl)-1,7-bis (4-methoxy-phenyl) perylene-3,4,9,10-tetracarboxydiimide (MPPDI) was demonstrated. Strong absorption resulted from the broadband absorption of MPPDI at visible range and plasmon-enhanced absorption around 420 nm of Ag nanoparticles. Ag dopants in MPPDI acted as quenchers, which resulted in a dramatic decrease in photoluminescence intensity of MPPDI. Besides, J-V characteristics of Ag:MPPDI thin film changed from trapped-charge-limited current to Ohmic conduction with increasing Ag concentrations. Conductivity of 1.15×10-6 Ω cm was achieved when MPPDI/Ag=5:1. This organic thin film has potential applications for low-reflectance organic light-emitting diode and organic photovoltaic device. [ABSTRACT FROM AUTHOR]

In this paper we report on the optical properties of a series of GaN/AlGaN multiple quantum well structures grown on a-plane (1120) GaN, which had been deposited on r-plane (1102) sapphire substrates, compared to a reference GaN template of the same orientation. The low temperature photoluminescence spectrum of the template layer is dominated by two emission bands, which we attribute to recombination involving excitons in the bulk of the layer and electrons and holes trapped at basal-plane stacking faults, designated X1 and X2, respectively. The photoluminescence spectra from the quantum well structures show similar emission bands except that both X1 and X2 shift to higher energy with decreasing quantum well thickness. The shift to higher energy is due to the effects of quantum confinement on carriers trapped at the stacking faults that intersect the quantum wells, as well as those excitons that are localized within the quantum wells. This assignment is based partly on excitation spectroscopy that reveals exciton transitions associated with electrons from the n=1 and n=2 quantum well confined states. [ABSTRACT FROM AUTHOR]

This paper examines the influence of rapid thermal annealing on the photoluminescence spectra of self-assembled InAs/InP(001) quantum dots capped with 760 nm InP deposited at a reduced temperature. The capping layer contained a large concentration of point defects that can promote interdiffusion upon annealing. The onset temperature for measurable blueshift in the emission spectra was found to be ∼600 °C whereas shifts of 270 meV were obtained after annealing at 750 °C for 300 s. Gradual etching of the InP capping layer enabled to progressively quench energy shifts upon annealing, a promising result for spatially selective emission tuning. [ABSTRACT FROM AUTHOR]

The use of photoluminescence excited with two-photon process for characterizing the defect and impurity level in wide-gap semiconductor is discussed in this paper. Defects of polycrystalline zinc selenide (ZnSe) is observed deep inside the crystal. Two types of defects can be detected based on the spectral luminescence image. One type of defect can be seen in the entire spectrum images. Meanwhile, other types of defects can only be observed at higher energy of the spectrum, from 460 to 465 nm. This study represents works of identifying crystals defect in wide gap materials by two-photon luminescence technique. [ABSTRACT FROM AUTHOR]