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Dislocations are generated in Si wafers during flash lamp annealing for 20 ms. The samples have been etched to different depths and macro‐photoluminescence (PL) spectra have been recorded for different dislocation densities. A micro‐PL investigation is also carried out on a cross section of a sample. Four characteristic emission peaks are found, which are the well‐known D1, D2, D3, and D4 lines. The findings demonstrate a significant influence of the defect densities on the PL spectra of the D lines by using both the micro‐ and the macro‐PL setups, and show a correlation of the PL intensities with etch pit density measured against the depth of the wafer. Additionally, the D lines dependency on temperature is explored, offering insights into the underlying mechanisms. The D lines exhibit a pronounced temperature dependence, which can be attributed to various factors including phonon interactions and thermal expansion effects. The influence of nickel contamination is also examined. [ABSTRACT FROM AUTHOR]

To investigate nonradiative recombination processes in indium gallium nitride (InGaN)‐based red light‐emitting diodes (LEDs), an InGaN‐based red LED with a hybrid quantum well (QW) structure consisting of red and blue single quantum wells (SQWs) is characterized by micro‐photoluminescence (μ‐PL) spectroscopy. The μ‐PL mapping of the red emission reveals numerous dark spots with various sizes and contrasts. Not only the red and blue (from a blue SQW) but green emission bands are observed at some red dark spots, suggesting that indium (In) segregation is one of the causes of nonradiative recombination in the red emission. Comparing the blue and green emission images to the red emission image reveals that the dark spots in the intensity map of the red emission can be classified into four types. Through this correlative analysis, the red dark spots associated with the dark areas in the intensity map of the blue emission are attributed to the major nonradiative recombination centers in the red emission. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are widely used as next-generation light sources because of their various advantages. However, their luminous efficiency is remarkably low at the green-emission wavelength. The luminous efficiencies of InGaN/GaN quantum wells (QWs) significantly decrease with increasing indium content in the green wavelength region, mainly owing to the quantum-confined Stark effect (QCSE). This green gap problem can be solved using QWs grown on semi-polar GaN substrates, such as the {11–22} planes, to reduce the QCSE. We propose that the use of surface plasmons (SPs) is a promising way to improve the light emission efficiency of light-emitting materials such as InGaN/GaN QWs. SP resonance increases the spontaneous emission rates of the excited states, causes a relative reduction in non-radiative relaxation, and ultimately increases the internal quantum efficiencies. In this study, the light emissions of InGaN/GaN QWs grown on polar and semi-polar GaN were investigated using micro-photoluminescence (PL). We successfully enhanced the light emission of semi-polar GaN via SP resonance. The PL peak intensities and wavelengths were mapped and compared to determine the underlying mechanisms. We also measured the emission lifetimes by time-resolved PL and interpreted the detailed mechanism of SP-enhanced emissions. It was found that SP resonances can control not only the emission efficiency but also the exciton dynamics, such as exciton localization effects, QCSE screening, and defect level saturation. We conclude that the green gap problem can be solved by SP-enhanced light emission in semipolar InGaN/GaN.

Ultra-thin Zinc oxide nanowires were prepared by a simple thermal evaporation method using a suitable amount of lead sulfide as an additive. It has been found that the nanowires are single crystalline of zincate grown along [1 0 1] direction. The transmission electron microscopy images show that nanowires consist of smooth ultra-thin cantilever-like with a diameter in the range of 10–20 nanometer (nm) and length of few microns. At room temperature, the photoluminescence spectra exhibit unusual strong broad peaks extending from the visible to near infrared (∼500–800 nm). The synthesized nanowires can serve as a novel platform for electrochemical and nano-biomolecular applications. [ABSTRACT FROM AUTHOR]

Self‐assembled nanocrystals (NCs) into superlattices (SLs) are alternative materials to polycrystalline films and single crystals, which can behave very differently from their constituents, especially when they interact coherently with each other. This work concentrates on the Superradiance (SR) emission observed in SLs formed by CsPbBr3 and CsPbBrI2 NCs. Micro‐Photoluminescence spectra and transients in the temperature range 4–100 K are measured in SLs to extract information about the SR states and uncoupled domains of NCs. For CsPbBr3 SLs with mostly homogeneous SR lines (linewidth 1–5 meV), this work measures lifetimes as short as 160 ps, 10 times lower than the value measured in a thin film made with the same NCs, which is due to domains of near identical NCs formed by 1000 to 40 000 NCs coupled by dipole–dipole interaction. The thermal decoherence of the SR exciton state is evident above 25 K due to its coupling with an effective phonon energy of ≈8 meV. These findings are an important step toward understanding the SR emission enhancement factor and the thermal dephasing process in perovskite SLs. [ABSTRACT FROM AUTHOR]

The active channels in AlGaN/GaN‐based heterostructures are studied under different applied electrical fields to identify the Joule heating factors affecting the temperature values in the channels. The temperature in active channels of two different lengths (30 and 180 µm) is characterized using optical methods, and electrical methods are used as a reference. The technique of optical thermometry is based on the data of micro‐photoluminescence and micro‐Raman experiments. The electrical method is based on the measurements of current–voltage characteristics for comparison. It is shown that photoluminescence‐ and electrical‐based temperature values demonstrate similar behavior and good correlation. The Raman‐based method, exploiting the temperature dependence of the frequency position of E2high vibrational band in GaN, shows a significant deviation compared with electrical‐ and luminescence‐based methods. This deviation is shown to be related to the residual mechanical strain in the layered structure and the formation of hot phonons. The influence of hot phonons and mechanical strain effects increases at high electrical load (>5 kV cm−1) and at high temperatures (>400 °C), respectively. [ABSTRACT FROM AUTHOR]

Detailed studies of the luminescent properties of the Si-based 2D photonic crystal (PhC) slabs with air holes of various depths are reported. Ge self-assembled quantum dots served as an internal light source. It was obtained that changing the air hole depth is a powerful tool which allows tuning of the optical properties of the PhC. It was shown that increasing the depth of the holes in the PhC has complex influences on its overall photoluminescence (PL) response due to the simultaneous influences of counteracting factors. As a result, the maximal increase in the PL signal of more than two orders of magnitude was obtained for some intermediate, but not full, depth of the PhC's air holes. It was demonstrated that it is possible to engineer the PhC band structure in such a way as to construct specific states, namely bound states in continuum (BIC), with specially designed dispersion curves being relatively flat. In this case, such states manifest themselves as sharp peaks in the PL spectra, and have high Q-factors which are larger than those of radiative modes and other BIC modes without such a flat dispersion characteristic. [ABSTRACT FROM AUTHOR]

Abstract The active channels in AlGaN/GaN‐based heterostructures are studied under different applied electrical fields to identify the Joule heating factors affecting the temperature values in the channels. The temperature in active channels of two different lengths (30 and 180 µm) is characterized using optical methods, and electrical methods are used as a reference. The technique of optical thermometry is based on the data of micro‐photoluminescence and micro‐Raman experiments. The electrical method is based on the measurements of current–voltage characteristics for comparison. It is shown that photoluminescence‐ and electrical‐based temperature values demonstrate similar behavior and good correlation. The Raman‐based method, exploiting the temperature dependence of the frequency position of E2high vibrational band in GaN, shows a significant deviation compared with electrical‐ and luminescence‐based methods. This deviation is shown to be related to the residual mechanical strain in the layered structure and the formation of hot phonons. The influence of hot phonons and mechanical strain effects increases at high electrical load (>5 kV cm−1) and at high temperatures (>400 °C), respectively.

The efficiency of back‐contact perovskite solar cells has steadily increased over the past few years and now exceeds 11%, with interest in these devices shifting from proof‐of‐concept to viable technology. In order to make further improvements in the efficiency of these devices it is necessary to understand the cause of the low fill factor, low open‐circuit voltage (VOC), and severe hysteresis. Here a time‐dependent Suns‐Voc and Suns‐photoluminescence (PL) analysis are performed to monitor the transient ideality factor spatially. Two sets of quasi‐interdigitated back‐contact perovskite solar cells are studied; cells with and without a mesoporous TiO2 layer. Maps of the PL intensity and ideality factor resemble the periodic structure of the back‐contact electrodes and the transient behavior exhibit distinct features such as a temporary variation in the periodicity of the modulation, spatial phase shifting, and phase offsets. It is shown that the presence of the mesoporous layer greatly reduces recombination, increasing the VOC by 0.12 V. Coupled 2D time‐dependent drift‐diffusion simulations allow the experimental results to be modeled, and replicate the key features observed experimentally. They reveal that non‐uniform ion distribution along the transport layer interfaces can drastically alter the PL intensity and ideality factor throughout the device. [ABSTRACT FROM AUTHOR]

In this study, Yb3+-Er3+-Tm3+ doped Y2O3 microspheres were synthesized using the solvothermal method. Structural, morphological, and elemental analysis was done using XRD, FESEM, and EDX characterization techniques. The optical properties of the samples were determined using UVâ€"Vis-NIR spectroscopy and upconversion photoluminescence measurements. The anti-Stokes emission peaks from these polycrystalline phosphor microspheres were obtained using a commercial micro-photoluminescence setup equipped with a 976 nm laser as an excitation source at room temperature. It was compared with the emission spectra taken from a 2â€"3 mm spot size of 976 nm laser irradiation on the same sample. The micro-emission spectra were analyzed based on possible Stark splitting energy level transitions between the 2S+1LJ manifolds of Er3+ and Tm3+ ions. A detailed mechanism is outlined for emission in the entire visible region under 976 nm laser excitation. [ABSTRACT FROM AUTHOR]

We measure low-temperature micro-photoluminescence spectra along a MoS 2 nanotube, which exhibit the peaks of the optical whispering gallery modes below the exciton resonance. The energy fluctuation and width of these peaks are determined by the changes of the nanotube wall thickness and propagation of the optical modes along the nanotube axis, respectively. We demonstrate the potential of the high-quality nanotubes for realization of the strong coupling between exciton and optical modes when the Rabi splitting can reach 400 meV. We show how the formation of exciton-polaritons in such structures will be manifested in the micro-photoluminescence spectra and analyze the conditions needed to realize that.

Abstract We investigated strontium oxide (SrO) as an interlayer material to enhance the UV stability of a CH 3 NH 3 PbI 3 perovskite solar cell. Moisture and over 400 nm wavelength of light were excluded to investigate the effect of UV light only. Two different interlayer fabrication processes were examined to optimize the performance of this solar cell. Devices fabricated by dipping for 30 min in SrO solution exhibited photoconversion efficiencies of 15.5%, whereas those fabricated with 60-min dipping showed photoconversion efficiencies of 15% and exhibited local Sr agglomeration. Devices with SrO displayed lower initial efficiencies than those without any SrO layer (17.6%), However, a device without SrO retained only 34.4% of its initial efficiency after 100 h of UV exposure. In contrast, SrO-incorporated devices retained almost 60.0% of their initial efficiency. Severe μ-PL mapping intensity degradation was observed in devices that did not include the interlayer, but no degradation was observed in those with the SrO interlayer. This can be attributed to the passivation of the degradation sites by SrO. Graphical abstract Image 1 Highlights • Perovskite UV stability was tested under conditions except moisture, oxygen and wavelengths exceeding 400 nm. • With high resolution μ-PL mapping technique, direct evidence is provided about the area perovskite UV degradation begins. • UV degradation is initiated at the ETL/perovskite interface. • Effect of the SrO interlayer on UV stability was examined in an inert atmosphere. • UV stability is enhanced by SrO interface passivation. [ABSTRACT FROM AUTHOR]

We present a conceptual approach for the localisation and characterisation of local sites of recombination in high diffusion length semiconductors under photovoltaic field conditions. While established imaging techniques operate in this very regime of uniform "1 sun" illumination, inevitable lateral diffusion of charge carriers veils the origin and severity of localised recombination sites. To reduce this limitation due to lateral diffusion the natural choice is using focussed charge carrier excitation and detection in combination with scanning the specimen. The resulting photoluminescence intensity maps are of high spatial resolution and may be composed of a superposition of a multitude of recombination active defects influencing each other due to the high bulk diffusion length. We demonstrate the feasibility of a self-consistent calibration of the setup quantum efficiency in such experimental condition which delivers a charge carrier density map in absolute units. A solution is presented to disentangle the superposition of local sites of recombination to isolate the actual recombination activity of every site. We demonstrate the feasibility of the approach experimentally on the high diffusion length semiconductor silicon. [Display omitted] • Understanding micro-PL measurements on long diffusion length semiconductors. • Detailed theoretical and conceptual discussion: what can be measured? • Self-consistent calibration of absolute photoluminescence intensities. • Retrieving recombination rate of superposed local sites of recombination. • Demonstration on epitaxially gown silicon with structural defects. [ABSTRACT FROM AUTHOR]

Erbium-doped SiO 2 -TiO 2 thin films were prepared by the sol-gel method, using erbium nitrate pentahydrate powder, tetraethyl-orthosilicate (TEOS), and titanium tetraisopropoxide (TTIP) as precursors. The Si/Ti ratios in the SiO 2 -TiO 2 films agree with the TEOS/TTIP molar ratio in the sol-gel precursor. Atomic coordination structure of erbium was defined by extended X-ray absorption fine structure spectrometry (EXAFS) and optical properties of the films were characterized by micro-photoluminescence (Micro-PL). The first-neighbor-shell coordination number of erbium in SiO 2 -TiO 2 thin films would influence the optical properties. The 700 °C-annealed 80%SiO 2 -20%TiO 2 :Er1.0% (mol%) film with the lowest coordination number exhibits the highest photoluminescence intensity. Moreover, Fourier transform infrared spectroscopy (FTIR) analysis reveals that the main bonding structures of SiO 2 -TiO 2 thin films are related to the erbium dopants. The modification of microstructure and chemical bonding configuration in the SiO 2 -TiO 2 films by the Er-doping concentration and its influence on the optical properties are discussed. [ABSTRACT FROM AUTHOR]

Spin-related emission properties have important applications in the future information technology; however, they involve microscopic ferromagnetic coupling, antiferromagnetic or ferrimagnetic coupling between transition metal ions and excitons, or d state coupling with phonons is not well understood in these diluted magnetic semiconductors (DMS). Fe3+ doped ZnSe nanoribbons, as a DMS example, have been successfully prepared by a thermal evaporation method. Their power-dependent micro-photoluminescence (PL) spectra and temperature-dependent PL spectra of a single ZnSe:Fe nanoribbon have been obtained and demonstrated that alio-valence ion doping diminishes the exciton magnetic polaron (EMP) effect by introducing exceeded charges. The d-d transition emission peaks of Fe3+ assigned to the 4T2 (G) → 4A1 (S) transition at 553 nm and 4T1 (G) → 4A1 (S) transition at 630 nm in the ZnSe lattice have been observed. The emission lifetimes and their temperature dependences have been obtained, which reflected different spin-phonon interactions. There exists a sharp decrease of PL lifetime at about 60 K, which hints at a magnetic phase transition. These spin-spin and spin-phonon interaction related PL phenomena are applicable in the future spin-related photonic nanodevices. [ABSTRACT FROM AUTHOR]

We report on the successful growth of strained core-shell GaAs/InGaAs nanowires on Si (111) substrates by molecular beam epitaxy. The as-grown nanowires have a density in the order of 10 cm, length between 3 and 3.5 μm, and diameter between 60 and 160 nm, depending on the shell growth duration. By applying a range of characterization techniques, we conclude that the In incorporation in the nanowires is on average significantly smaller than what is nominally expected based on two-dimensional growth calibrations and exhibits a gradient along the nanowire axis. On the other hand, the observation of sharp dot-like emission features in the micro-photoluminescence spectra of single nanowires in the 900-1000-nm spectral range highlights the co-existence of In-rich enclosures with In content locally exceeding 30 %. [ABSTRACT FROM AUTHOR]

We present the combination of two complementary microphotoluminescence spectroscopic techniques operating in transient and steady state condition, respectively. Introducing the time domain into the well-established micro-photoluminescence mapping approach operating under steady state conditions demonstrates a distinct improvement of the robustness and reliability in the determination of charge carrier lifetime measured with micrometer spatial resolution. Lifetimes from 50 ns to above ms are accessible. We elaborate a calibration procedure and apply the combined all-photoluminescence setup to high-performance multicrystalline silicon. A lifetime image obtained from the established photoluminescence imaging technique is reconstructed from the microscopic map by considering lateral diffusion and optical blurring, revealing a more detrimental influence of small angle grain boundaries as well as a higher lifetime within grains as may be deduced from the standard imaging technique. [ABSTRACT FROM AUTHOR]

In this paper, Micro-Raman spectroscopy and Micro-Photoluminescence techniques were utilized to quantify the residual stress in Al 0.26 Ga 0.74 N/GaN/Si HEMT's for unpassivated and passivated sample by SiO 2 /SiN layers. One of the issues that can impact device reliability of the HEMT's based GaN, is the mechanical stress induced in the structure. It has been observed that biaxial stress has a linear relationship with the Raman E 2 (high), A 1 (LO) mode and the luminescent band gap of GaN. A slight blue shift in the PL peak position indicates a compressive stress induced in the GaN layer close to 0.33 GPa and 0.99 GPa before and after passivation respectively, accompanied by a red shift in PL peak position of the Al 0.26 Ga 0.74 N barrier layer affirms the existence of a tensile stress around −1.28 GPa and −2.08 GPa for the unpassivated and passivated sample. [ABSTRACT FROM AUTHOR]

ZnO nanowires with average diameters of 50-200 nm were grown by chemical vapor deposition. Their gas sensing properties were analyzed by micro-photoluminescence spectroscopy allowing for optical readout. The influence of [ABSTRACT FROM AUTHOR]

Hydride Vapor Phase Epitaxy (HVPE) growth process is still efficient for the growth of high quality GaN material. In situ-characterization techniques are extremely difficult to implement inside HVPE hot wall reactors. A method based on selective area growth coupled to spatially resolved optical spectroscopies, micro-photoluminescence and micro-reflectivity is developed for a control of GaN optical quality and strain at different growth stages. As highly reproducible HVPE process is used with a two-step epitaxial lateral overgrowth procedure to produce 80 µm thick GaN layers presenting a weak residual strain with high optical quality comparable to free-standing GaN layers. [ABSTRACT FROM AUTHOR]

Spin-related emission properties have important applications in the future information technology; however, they involve microscopic ferromagnetic coupling, antiferromagnetic or ferrimagnetic coupling between transition metal ions and excitons, or d state coupling with phonons is not well understood in these diluted magnetic semiconductors (DMS). Fe3+ doped ZnSe nanoribbons, as a DMS example, have been successfully prepared by a thermal evaporation method. Their power-dependent micro-photoluminescence (PL) spectra and temperature-dependent PL spectra of a single ZnSe:Fe nanoribbon have been obtained and demonstrated that alio-valence ion doping diminishes the exciton magnetic polaron (EMP) effect by introducing exceeded charges. The d-d transition emission peaks of Fe3+ assigned to the 4T2 (G) → 6A1 (S) transition at 553 nm and 4T1 (G) → 6A1 (S) transition at 630 nm in the ZnSe lattice have been observed. The emission lifetimes and their temperature dependences have been obtained, which reflected different spin–phonon interactions. There exists a sharp decrease of PL lifetime at about 60 K, which hints at a magnetic phase transition. These spin–spin and spin–phonon interaction related PL phenomena are applicable in the future spin-related photonic nanodevices.

The micro-Raman and micro-photoluminescence spectra of non-conjugated and conjugated with antibody against S6K2 commercial CdSe/ZnS quantum dots (QDs) were investigated under different excitation wavelengths and at different temperatures. In the photoluminescence (PL) spectra, the additional PL band shifted on 0.6–0.65 eV to higher energies from the CdSe/ZnS QD exciton PL band is revealed. The relative intensity of this band is found to be several times larger in bio-conjugated QDs, than in the non-conjugated ones. The characteristics of both PL bands (the PL intensity, spectral position and half-width of the PL band) vary similarly under continuous laser light irradiation, storage of the QD samples in the atmospheric ambience as well as during the temperature change. In the Raman spectra recorded under excitation resonant with the high-energy PL band, the additional Raman peaks at about 300 cm−1 and 600 cm−1, which are close to the frequency of LO and 2LO phonons of bulk CdS, are found. It is proposed that alloyed QDs with chemical composition close to CdS are responsible for the additional high-energy PL band. The possible reasons for the formation of the alloyed QDs are discussed. [ABSTRACT FROM AUTHOR]

The progressive stacking of chalcogenide single layers gives rise to two-dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide (InSe) is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness (as large as 0.2 eV for three single layers). First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: ZnO micro-tetrapod microstructures were fabricated by a vapor phase transport method. Under the excitation of 325nm continuous wave He–Cd laser, the microphotoluminescence spectrum from a single ZnO micro-tetrapod presented a two-band structure with a series of optical resonance modes; a possible optical resonance loop formed in two adjacent legs of the tetrapod was suggested, and the two-band spectrum structure was attributed to the exciton–exciton scattering process. The lasing emission was obtained from single ZnO micro-tetrapod under intense excitation of 355nm nanosecond pulsed laser. The lasing spectrum shows clear mode structure with the lasing quality factor of 1300 and the lasing threshold of 150kW/cm2. The microphotoluminescence resonance and lasing results indicate that ZnO tetrapod can serve as a high-Q ultraviolet microcavity laser. [Copyright &y& Elsevier]

Abstract: The change of the photoluminescence (PL) and optical characteristics in non-conjugated and conjugated with S6K2 antibody CdSe/ZnS core/shell quantum dots (QDs) during storage in air has been studied by the conventional PL, micro-PL and micro-Raman techniques. The QDs dried on a crystalline Si substrate were kept in the darkness and under illumination. In the PL spectra, the storage resulted in a blue shift of PL peak position, in the increasing of the full width at a half maximum (FWHM) of the PL band and in the decreasing of the PL intensity. In the Raman spectra, the shift of the CdSe LO peak position to the low frequency region and the increasing of its FWHM were observed. The transformations in the PL and optical characteristics correlate with each other and are found to be the largest in bio-conjugated QDs stored under illumination. The increase of the light intensity accelerated the changes occurred during storage. An oxidation of the QD core, which decreases the QD size, is supposed to be responsible for observed transformations. The bio-conjugation is assumed to promote QD oxidation that results in different PL peak position in stored non-conjugated and bio-conjugated QDs. The mechanism of the effect is discussed. [Copyright &y& Elsevier]

Nanoscale heterostructures with modulated composition and/or passivated interfaces can enrich/enhance the performance of diverse compact devices. Here, we report the synthesis of nanoscale pearl-like InP nanowire heterostructures wrapped with InP quantum dots (QDs)-decorated P xO y nanospheres periodically along the length by a chemical vapor deposition (CVD) method. Compared with the Raman modes of bulk InP, additional surface phonon (SP) peak, which results from InP QDs finite size, is observed in these pearl-like heterostructures. Room-temperature photoluminescence (PL) showed that these pearl-like heterostructures simultaneously exhibited two broad emission bands at 768 and 846 nm, which belong to the PL emission of InP QDs and InP trunks, respectively. The significant blue shift of the two emission bands compared with the intrinsic luminescence of InP crystal at 920 nm is attributed to the quantum confinement effects. A self-organization model is proposed to illustrate the formation of the heterostructures. These interesting pearl-like InP/P xO y heterostructures may find potential applications in constructing new nanoscale optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract: Luminescence of Zn4In2O7 nanobelts and microplates synthesized by a thermal evaporation–deposition method, has been investigated by photoluminescence (PL) and cathodoluminescence (CL) in the scanning electron microscope (SEM). Time resolved and temperature dependent CL measurements show that an emission at 2.37eV appears to be characteristic of the Indium–Zinc–Oxide (IZO) compound investigated. PL and waveguiding behavior of the microplates is described. Raman spectra of the structures as a function of In content has been studied. [Copyright &y& Elsevier]

A method to improve the growth repeatability of low-density InAs/GaAs self-assembled quantum dots by molecular beam epitaxy is reported. A sacrificed InAs layer was deposited firstly to determine in situ the accurate parameters of two- to three-dimensional transitions by observation of reflection high-energy electron diffraction patterns, and then the InAs layer annealed immediately before the growth of the low-density InAs quantum dots (QDs). It is confirmed by micro-photoluminescence that control repeatability of low-density QD growth is improved averagely to about 80% which is much higher than that of the QD samples without using a sacrificed InAs layer. [ABSTRACT FROM AUTHOR]

Abstract: Epitaxial emitters deposited by atmospheric pressure CVD have been studied using different characterization methods such as spreading resistance profiling (SRP) or electrochemical capacitance voltage profiling (ECV). Comparing simulations with measured data, very low minority carrier lifetimes of τeff = 20μs have been determined for FZ-material after a standard epitaxy process. LBIC measurements showed very low and inhomogeneous distributed diffusion lengths in the range of 100-250μm before process optimization. Therefore an emitter epitaxy process working at lower temperatures was developed [1] leading to diffusion lengths of 750μm. The effective minority carrier lifetimes and emitter saturation currents were determined using QSSPC measurements. For samples with an emitter, deposited at optimized temperature, a best value for the effective minority carrier lifetime of τeff = 212μs was measured and an emitter saturation current could be determined to J0e= 46 fA/cm2. In order to investigate the stress in the epitaxial layers μRaman and μPL measurements were performed showing no increased values at the interface. The doping density in boron doped emitters was determined with μPL and in good agreement with measured ECV-profiles. The Shockley-Read-Hall lifetime in the emitter bulk showed no increased values at the interface between substrate and epitaxial layer. [Copyright &y& Elsevier]

Abstract: We report on a comparative micro-photoluminescence investigation of ZnO hexagonal nanopillars (HNPs) and the seeding layer grown on the off-axis 4H-SiC substrate. Transmission electron microscope (TEM) results establish that a thin seeding layer continuously covers the terraces of 4H-SiC prior to the growth of ZnO HNPs. Low temperature photoluminescence (LTPL) shows that ZnO HNPs are only dominated by strong donor bound exciton emissions without any deep level emissions. Micro-LTPL mapping demonstrates that this is specific also for the seeding layer. To further understand the recombination mechanisms, time-resolved micro-PL spectra (micro-TRPL) have been collected at 5K and identical bi-exponential decays have been found on both the HNPs and seeding layer. Temperature-dependent TRPL indicates that the decay time of donor bound exciton is mainly determined by the contributions of non-radiative recombinations. This could be explained by the TEM observation of the non-radiative defects in both the seeding layer and HNPs, like domain boundaries and dislocations, generated at the ZnO/SiC interface due to biaxial strain. [Copyright &y& Elsevier]

Abstract: μ-Raman and μ-photoluminescence methods have been employed to investigate microscopic spatial stress distribution and optical properties of GaN films grown on the convex shape-patterned sapphire substrate (CSPSS). By comparison of the μ-Raman and μ-PL spectra, we found that significantly large difference, Δσ xx ∼0.46GPa, in biaxial compressive stress between the flat trench and convex regions in the side facet of the GaN film, around ∼2μm below the surface whereas on the GaN surface, little difference with large residual stress was observed in both regions compared to those from the side facet. Temperature dependent and time-resolved photoluminescence spectra have shown that the GaN film grown on the CSPSS has improved crystal purity through the reduction of intrinsic point defects. [ABSTRACT FROM AUTHOR]

Pure ZnO hexagonal microwires and Fe(III)-doped ZnO microwires (MWs) with a novel rectangular cross section were synthesized in a confined chamber by a convenient one-step thermal evaporation method. An oriented attachment mechanism is consistent with a vapor-solid growth process. Photoluminescence (PL) and Raman spectroscopy of the Fe(III)-doped ZnO MWs and in situ spectral mappings indicate a quasi-periodic distribution of Fe(III) along a one-dimensional (1-D) superlattice ZnO:ZnFe2O4 wire, while PL mapping shows the presence of optical multicavities and related multimodes. The PL spectra at room temperature show weak near-edge doublets (376 nm and 383 nm) and a broad band (450–650 nm) composed of strong discrete lines, due to a 1-D photonic crystal structure. Such a 1-D coupled optical cavity material may find many applications in future photonic and spintronic devices. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: We have studied micro-photoluminescence spectra of a self-assembled single GaAs quantum dot under 8 K. With strong pulsed excitation, the micro-photoluminescence spectrum shows bright emission lines originated from an exciton, a positively charged exciton, and a biexciton, together with weak lower energy emissions reflecting multi-excitonic structures with more carriers. We have identified the origins of these weak emission lines, and showed the existence of charged biexciton states, through single photon correlation measurements and excitation power dependence of the photoluminescence intensity. In addition, investigating the radiative recombination process of the charged biexciton, we have determined the electron–hole exchange energy in the GaAs quantum dot. [Copyright &y& Elsevier]

Abstract: In the present work, we report the effect of low-energy ion bombardment on CdTe surfaces. The effect is revealed by FESEM images and photoluminescence (PL) measurements carried out before and after irradiation of CdTe polycrystals by means of an ion-beam sputtering (IBS) system. An important improvement in the luminescence of CdTe was observed in the irradiated areas, related to defect-free surfaces. [Copyright &y& Elsevier]

Abstract: Continuous wave- and time-resolved micro-photoluminescence spectroscopy has been performed on single InAs self-assembled quantum dots grown on GaAs. The presence of residual impurities (donors and acceptors) in samples with low dot density opens the possibility to switch from trion to neutral exciton states inside quantum dots by selective optical pumping. We propose a microstate model to describe the recombination dynamics of all the excitonic especies (neutral exciton, positive/negative trion and biexciton) under the considered optical pumping conditions when increasing the excitation power. [Copyright &y& Elsevier]

Abstract: We fabricated ordered GaAs/AlGaAs quantum dots (QDs) on patterned GaAs(001) substrates and investigated their optical properties by micro-photoluminescence (-PL) spectroscopy. Sharp excitonic lines with single photon emission properties were observed. Polarization-dependent PL was performed to resolve the optical fine structure splitting of neutral excitonic lines and to identify the neutral biexciton line. [Copyright &y& Elsevier]

Abstract: We report on double-quantum dot (QD) molecules realized with modulated quantum wire (QWR) heterostructures by self-limiting growth of AlGaAs alloys in inverted tetrahedral pyramids. The QWR barriers connecting the dots facilitate the tunnel-coupling between the confined carriers. Evidences for the presence of such coupling are provided by conventional micro-photoluminescence measurements and theoretical modeling. Systematically tuning the relative QD sizes in the QD molecules reveals spectral line splitting consistent with the expected level splitting due to carrier hybridization. Prospects for extension of these structures to larger QD superlattices are discussed. [Copyright &y& Elsevier]

Abstract: We study the exciton states of vertically coupled InAlAs/AlGaAs self-assembled quantum dot (QD) pairs which were designed to have different wetting-layer edges in two QD layers. From a single QD pair, micro-photoluminescence demonstrates four exciton s levels as a result of interdot coupling. Consistent with theory, such a level can be split into four sub-levels. In general, 2-fold splitting is exhibited by the doublet under magnetic field. The doublet is of near-circular polarization in one side but of near-linear polarization in the other side. This abnormal behavior might be understood by heavy hole–light hole mixing. The other 2-fold splitting is observed by photoluminescence excitation measurement without magnetic field. This splitting is suggested resulting from the spatial asymmetry of the coupled QD pair. It is possible that these two split states are robust against magnetic field, and are selectively excited by using pump energy associated with different wetting layers. [Copyright &y& Elsevier]

We report on the magneto-optical study of spin polarized energetic fine structures for exciton complex in single CdSe quantum dot (QD) by using micro- photoluminescence (micro-PL) spectroscopy. The zero-field splitting of exciton luminescence peak arisen from the anisotropic exchange interaction of carriers in the QDs was observed. The g-factors for exciton and negatively-charged exciton, i.e. trion in a single QD were determined by fitting the magnetic field dependence of the corresponding PL peaks. By exciting the single QD with circularly polarized light of σ- and σ+ polarization, the spin-up and spin-down trions were selectively generated. The ratio, τ/τsf, of the exciton lifetime and the time constants for the spin-flipping process of trion in a single QD was estimated to be 0.13, which implies a long spin-lifetime in single CdSe QD. [ABSTRACT FROM AUTHOR]

Abstract: We have studied multi-excitonic energy levels confined in single GaAs/AlGaAs quantum dots grown by modified droplet epitaxy via micro-photoluminescence (μPL) measurements under a magnetic field. From the excitation intensity dependence of the μPL spectrum of a single GaAs Quantum dot, it is possible to see the emissions from multi-excitonic energy levels. By applying a magnetic field, splitting of the exciton line is observed. Similarly to the exciton line, the multi-exciton lines split with increasing magnetic field. It can be considered that the splitting of the multi-exciton lines arises from the exciton Zeeman splitting essentially. [Copyright &y& Elsevier]