Transition metal impurities are known to adversely affect the efficiency of electronic and optoelectronic devices by introducing midgap defect levels that can act as efficient Shockley-Read-Hall centers. Iron in GaN do not follow this pattern: their level is close conduction band hence far from midgap. Using hybrid functional first-principles calculations, we uncover properties Fe demonstrate its high a nonradiative center due recombination cycle involving excited states. Unintentional...

Degradation under high current stress of AlGaN quantum well based light emitting diodes at 285 and 310 nm has been studied using electroluminescence, time-resolved photoluminescence current-voltage experimental techniques. The measurements have revealed that during aging decrease the emission intensity is accompanied by increase tunneling current, nitrogen vacancy concentration partial compensation p-doping. main role in device degradation ascribed to formation conductivity channels,...

In this work, a novel CMOS compatible process for Si-based materials has been presented to form SiGe nanowires (NWs) on On Insulator (SGOI) wafers with unprecedented thermoelectric (TE) power factor (PF). The TE properties of NWs were characterized in back-gate configuration and physical model was applied explain the experimental data. carrier transport modified by biasing voltage gate at different temperatures. PF enhanced >2 comparison bulk over temperature range 273 K 450 K. This...

We report photo- and electroluminescence from an alternating conjugated polymer consisting of fluorene units low-band gap donor-acceptor-donor (D–A–D) units. The D–A–D segment includes two electron-donating thiophene rings combined with a thiadiazolo-quinoxaline unit, which is electron withdrawing to its nature. resulting has band 1.27 eV. corresponding electro- photoluminescence spectra both peak at approximately 1 μm. Light-emitting diodes, based on single layer the polymer, demonstrated...

Scanning near-field photoluminescence spectroscopy has been applied to evaluate bandgap fluctuations in epitaxial AlGaN films with the AlN molar fraction varying from 0.30 0.50. A dual localization pattern observed. The potential of small-scale (<100 nm) localization, evaluated width spectra, is between 0 and 51 meV increases increased Al content. These variations have assigned compositional occurring due stress variations, dislocations, formation Al-rich grains during growth. Larger...

By studying low radiative efficiency blue III-nitride light emitting diodes (LEDs), we find that the ABC model of recombination commonly used for understanding behavior in LEDs is insufficient and additional effects should be taken into account. We propose a modification to standard by incorporating bimolecular nonradiative term. The modified shown much better agreement with data more consistent than conventional very short carrier lifetimes measured time-resolved photoluminescence similar,...

Hole self-localization into polaron states is a phenomenon characteristic of many wide bandgap compounds including transparent semiconducting oxide β-Ga2O3. While this effect has been recognized for some time, its dynamics remained elusive, and often considered instantaneous. In work, using the two-color ultrafast pump–probe technique, we have measured hole time in At room temperature, found to be 0.5 ps increasing 1.1 at 10 K. terms configuration coordinate diagram, tunneling thermal...

Nonstoichiometric GaAs obtained by implantation with 2 MeV arsenic ions at 1015 cm−2 dose is studied. As-implanted samples show a <200 fs lifetime of photocarriers and low resistivity due to hopping, mobility less than 1 cm2/V s. Annealing the 600 °C leads substantial recovery postimplant damage, as seen from Rutherford backscattering channeling spectra increase about 2000 s, but photocarrier still ps. These parameters are similar those low-temperature annealed °C, make implanted an...

To assess the impact of random alloying on optical properties InGaN alloy, high-quality InxGa1−xN (0 < x 0.18) epilayers grown c-plane free-standing GaN substrates are characterized both structurally and optically. The thickness (25–100 nm) was adjusted to keep these layers pseudomorphically strained over whole range explored indium content as checked by x-ray diffraction measurements. evolution low temperature absorption (OA) edge linewidth a function energy, hence content, is...

Hole injection through V-defect sidewalls into all quantum wells (QWs) of long wavelength GaN light emitting diodes had previously been proposed as means to increase efficiency these devices. In this work, we directly tested the viability mechanism by electroluminescence and time-resolved photoluminescence measurements on a device in which QW furthest away from p-side structure was deeper, thus serving an optical detector for presence injected electron–hole pairs. Emission well confirmed...

The efficiency of high-power operation multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on the realization uniform hole distribution between QWs. In long wavelength InGaN/GaN QW LEDs, thermionic interwell transport is hindered by high GaN barriers. However, in polar LED structures, these barriers may be circumvented lateral injection via semipolar 101¯1 QWs that form facets V-defects. such carrier transfer time since competed recombination. this work, we...

The efficiency of operation GaN-based light emitting diodes (LEDs) to a large degree relies on realization uniform hole distribution between multiple quantum wells (QWs) the active region. Since direct thermionic transport QWs is inefficient, injection through semipolar 101¯1 that form facets V-defects has been suggested as an alternative approach. However, for efficient LED operation, carrier should be not only vertically, but also laterally, within individual QWs. In this work, lateral in...

The efficiency of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on uniformity hole distribution between the QWs. Typically, transport QWs takes place via carrier capture into and thermionic emission out In InGaN/GaN QWs, is hindered by high confinement polarization barriers. To overcome this drawback, injection through semipolar located at sidewalls V-defects had been proposed. However, in case V-defect injection, strong lateral variations take place....

Undoped In0.53Ga0.47As epilayers were implanted with 2-MeV Fe+ ions at doses of 1×1015 and 1×1016 cm−2 room temperature annealed temperatures between 500 800 °C. Hall-effect measurements show that after annealing, layers resistivities on the order 105 Ω/square can be achieved. Carrier lifetimes as short 300 fs are observed for samples 600 For higher annealing temperatures, characteristic times optical response a few picoseconds.

Carrier trapping of Fe3+/Fe2+ deep acceptors in epitaxially grown GaN:Fe on sapphire was studied by time-resolved photoluminescence. For the investigated Fe doping levels order 1018 cm−3, luminescence decay times are strongly dependent concentration, indicating that centers act as predominant nonradiative recombination channels. Linear dependence time iron concentration allows estimation electron capture cross-section for Fe3+ ions, which is equal to 1.9 × 10−15 cm2. The upper bound hole...

Scanning near field optical microscopy (SNOM) was applied to study the carrier localization in single InGaN/GaN quantum well structures grown on nonpolar m-plane GaN substrates. Dual potential consisting of hundreds nanometers- micrometer-size areas as smaller centers were identified from SNOM scans and photoluminescence spectral widths. The found align along [0001] direction, which attributed partial strain relaxation at monolayer steps.

Very high polarization degree of 0.98, considerably larger than theoretical predictions, has been measured in (202¯1¯) In0.24Ga0.76N/GaN quantum well by low temperature photoluminescence. With increasing temperature, the decreases due to thermal population excited valence band level. This effect suggests an accurate method determine interlevel energy, which, for studied well, is 32 meV. Time-resolved photoluminescence measurements set radiative recombination times between 2 and 12 ns...

A multimode scanning near-field optical microscopy technique that allows the mapping of surface morphology, photoluminescence (PL) spectra in illumination and illumination-collection modes, PL dynamics, all one scan, has been developed along with a method to use it for evaluation carrier diffusion. The measuring diffusion lengths as small ∼100 nm their anisotropy spatial distribution, parameters remaining inaccessible conventional far-field techniques. procedure applied study ambipolar...

Fe doped GaN was studied by time-resolved photoluminescence (PL) spectroscopy. The shape of PL transients at different temperatures and excitation powers allowed discrimination between electron hole capture to Fe3+ Fe2+ centers, respectively. Analysis the internal structure ions intra-ion relaxation rates suggests that for high repetition photoexciting laser pulses trapping takes place in excited state rather than ground ions. Hence, estimated coefficients 5.5 × 10−8 cm3/s 1.8 should be...

Uniform carrier distribution between quantum wells (QWs) of multiple QW light emitting diodes (LEDs) and laser is important for the efficiency device operation. In lasers, uniform ensures that all QWs contribute to lasing; in LEDs, it enables high power operation with minimal Auger losses a maximal efficiency. The takes place via interwell (IW) transport. polar GaN-based structures, transport might be hindered by strong confinement internal electric fields. this work, we study IW...

Abstract The optical response of hierarchical materials is convoluted, which hinders their direct study and property control. Transparent wood (TW) an emerging biocomposite in this category, adds function to the structural properties wood. Nano‐ microscale inhomogeneities composition, structure, at interfaces strongly affect light transmission haze. While interface manipulation can tailor TW properties, realization optically clear requires detailed understanding light–TW interaction...

Time-resolved photoluminescence measurements performed on proton implanted and annealed GaN layers have shown that carrier lifetime can be tuned over two orders of magnitude and, at implantation dose 1×1015 cm−2, decreases down to a few picoseconds. With annealing temperatures between 250 750 °C, lifetime, contrary electrical characteristics, is only slightly restored, indicating compensation dynamics are governed by different defects. Ga vacancies, free bound threading dislocations,...

Emission from a 285 nm AlGaN quantum well light emitting diode has been studied by scanning near-field optical spectroscopy. The scans revealed micrometer-size domainlike areas with higher intensity and at longer wavelength; presumably, because of lower AlN molar fraction in these regions. Experiments performed on different days have shown that time, spots increases emission wavelength shifts to the red, indicating further change alloy composition. This allowed distinguishing an aging...