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Background: Dialysis and kidney transplant patients are vulnerable populations for COVID-19 related disease and mortality. Methods: We conducted a prospective study exploring the eight week time course of specific cellular (interferon-I³ release assay and flow cytometry) or/and humoral immune responses (ELISA) to SARS-CoV-2 boost vaccination in more than 3100 participants including medical personnel, dialysis patients and kidney transplant recipients using mRNA vaccines BNT162b2 or mRNA-1273. Results: SARS-CoV-2-vaccination induced seroconversion efficacy in dialysis patients was similar to medical personnel (> 95%), but markedly impaired in kidney transplant recipients (42%). T-cellular immunity largely mimicked humoral results. Major risk factors of seroconversion failure were immunosuppressive drug number and type (belatacept, MMF-MPA, calcineurin-inhibitors) as well as vaccine type (BNT162b2 mRNA). Seroconversion rates induced by mRNA-1273 compared to BNT162b2 vaccine were 97% to 88% (p

The internal quantum efficiency (IQE) is a key property of light-emitting semiconductor structures. We critically review the most popular methods for determining the IQE. In particular, we discuss the impact of low- temperature non-radiative recombination on temperature-dependent CW photoluminescence measurements. Using temperature-dependent time-resolved photoluminescence we establish a method to verify 100 % IQE at low temperature and thus to obtain absolute internal quantum efficiencies at all temperatures.

Via temperature-dependent time-resolved photoluminescence spectroscopy, we investigate the radiative and nonradiative recombination processes in thin (quantum well widths of about 1.5 nm) a-plane, m-plane, () and () GaInN/GaN fivefold quantum well structures of varying indium content grown on low defect density GaN substrates and GaN templates. At room temperature, we observe surprisingly short radiative lifetimes in the range from 100 ps to 1 ns for these structures, being about one to two orders of magnitude shorter than for similar c-plane quantum wells. This large difference cannot solely be explained by the larger overlap matrix element in non- and semipolar wells. Higher exciton binding energies and lower effective density of states masses may contribute to an enhanced radiative probability. The nonradiative recombination exhibits a thermally activated behavior with activation energies of about 10 meV for () and around 25 meV for nonpolar quantum wells. These values are lower than the quantum well barrier height and the exciton binding energy, but in a similar range as the localization energies estimated from the radiative recombination.

We study the incorporation of indium into Al x Ga 1 − x N /GaN quantum well (QW) structures with high indium concentrations above 25% for QW thicknesses in the range 2 nm down to half a c -lattice constant under pulsed and continuous growth conditions. We want to clarify which processes limit the incorporation of indium and lead to a degrading layer structure. The data are discussed in the context of the adlayer proposed by theory (Northrup et al., 2000) [1] . The interplay of the adlayer with the incoming flux, the high desorption rate and segregation of indium can consistently explain the various observed phenomena.

In x Ga 1―x N/GaN quantum well (QW) structures grown on c-plane surfaces for long wavelength light emitters have been investigated intended. We reached indium concentrations of x In ≥ 0.35 with good optical and structural quality. For QW thicknesses d QW ≤ 2 nm a fully strained layer structure is observed. QWs of such high indium concentrations, however, are very sensitive to the growth conditions of the subsequent layers and thermal stability/degradation becomes an important issue. We modified the growth of the QWs to avoid or minimize V-pit formation without temperature ramping in the barriers and showed that their properties were unchanged when used in the active zone of a laser structure.

InxGa1� xN/GaN quantum well (QW) structures grown on c-plane and m-plane surfaces have been investigated intended for long wavelength light emitters. On c-plane InxGa1� xN QWs reached indium concentrations of xInX35% with good optical and structural quality. For QW thicknesses dQWp 2n m a fully strained layer structure is observed and the indium concentration is quite homogenous. Under the same growth conditions of the QW region we find similar or even slightly larger indium concentrations on m-plane surfaces. QWs of such high indium concentrations, however, are very sensitive to the growth conditions of the subsequent layers and we observe degradation such as indium outdiffusion or partial relaxation for high growth temperatures.

The efficiency droop in nitride LEDs is currently attributed to either carrier-density-dependent nonradiative recombination or to carrier leakage, both being discussed in terms of a single-particle picture. Our time-resolved photoluminescence results show that the radiative lifetime is independent of carrier density, while the nonradiative lifetime scales with the inverse of the carrier density. This can not be understood in a single-particle model. By means of a many-particle theory approach we obtain a consistent picture with both radiative and Auger recombination enhanced by excitonic electron-hole correlation. In the high carrier density limit single-particle radiative and Auger recombination are recovered.

Room-temperature electronic properties of semiconductors, especially in the case of higher charge densities, are commonly discussed in terms of single-particle excitations -- free electrons and holes. Many-particle effects, such as the formation of excitons (Coulomb-bound electron-hole pairs), are usually seen as low-temperature and low-density phenomena. In this paper, using ultrafast terahertz and photoluminescence measurements, the authors find that under certain conditions typical for wide-band-gap semiconductors, the radiative excitons can be efficiently formed at high charge density and at room temperature. This effect is believed to contribute to the extraordinarily high quantum efficiency of group III nitride light emitters.

In this paper, we critically review the usual explanation of the blue shift in the temperature dependence of the light emission, which is commonly observed for polar GaInN/GaN quantum wells at intermediate temperatures. We demonstrate that this blue shift is not necessarily caused by a thermally induced change of occupation in an inhomogeneously broadened density of states. Instead, different energy dependencies of radiative and nonradiative lifetimes may lead to an energy dependence of the internal quantum efficiency strongly influencing the peak position of the luminescence: the piezoelectric fields within the quantum well induce an approximately exponential relationship between the electron-hole overlap matrix element for the radiative transition between the lowest quantized states and the respective transition energy. Via time-resolved photoluminescence spectroscopy, we observe a corresponding exponential energy dependence of radiative lifetimes at low temperatures and almost energy independent nonradiative lifetimes toward room temperature throughout the emission of polar single quantum wells. An analytical model is demonstrated, predicting a significant blue shift of several 10 meV for polar and a negligible shift for nonpolar GaInN/GaN quantum wells at the transition from high to low internal quantum efficiency due to the energy-dependent competition between radiative and nonradiative recombination processes. This model consistently explains the lack of a blue shift in nonpolar quantum wells grown on $m$-plane bulk GaN as well as a reduced characteristic temperature for the onset of the blue shift after artificial defect generation via argon ion implantation.

Using time-resolved photoluminescence spectroscopy on GaInN/GaN multiple quantum well structures, we analyze the radiative and nonradiative processes contributing to the “green gap” in GaN-based light emitting devices. We observe that it is only partly caused by a reduced oscillator strength due to the Quantum Confined Stark Effect (QCSE) which becomes stronger with increasing indium concentration and well width. As the dominant effect we observe a reduction of nonradiative lifetimes when the indium concentration is increased. For higher indium concentrations, we find an additional nonradiative recombination path that might be attributed to an increased generation of defects like misfit dislocations, nitrogen vacancies and/or indium clusters within the optically active region. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this contribution, we quantitatively investigate nonradiative recombination due to argon implantation induced point defects in GaInN/GaN quantum wells via time-resolved photoluminescence spectroscopy. A significant reduction of carrier lifetimes in the QW is observed already for implantation doses of 1 × 10 11 cm -2 and higher due to nonradiative recombination at implantation defects. These new nonradiative processes exhibit thermal activation energies below 40 meV, therefore being a dominant loss mechanism at room temperature. The thermal stability of the defects has been analyzed using rapid thermal annealing (RTA) at 800°C and 850°C. We find a partial recovery of the nonradiative lifetimes after RTA indicating an elimination of some defects.

The basic principles of faraday isolation and thermal effects in the rod geometry under high power operation have been reviewed. The temperature dependency of the verdet-constant and the magnetization of NdFeB have been identified as the limiting factor of isolation ratio for an unchilled high power isolator device. The focal shift due to the isolator with rod-geometry is independent from beam diameter and strongly depending on beam quality. A highly compact isolator for unpolarized radiation up to 400 W fundamental mode for industrial application surrounding with minimal thermal lensing has been developed. At 400 W and 10-40 °C a transmission of 95-97 %, an isolation larger 20 dB, a thermal focus shift of less than 2 rayleigh ranges and a M2 smaller than 1.2 have been achieved.

The dependence of radiative and nonradiative lifetimes on the excess carrier density in GaInN/GaN quantum wells is studied via time-resolved photoluminescence spectroscopy over a wide range of excitation densities. Our results differ from the predictions of simple free-carrier models: density independent radiative lifetimes clearly evidence the excitonic nature even at room temperature. At high densities, nonradiative lifetimes are weakly temperature dependent and proportional to the inverse of the density, implying an excitonic, threshold-less Auger process. Furthermore, in the intermediate density regime between low and high injection, an increase of the nonradiative lifetimes is observed, which is typical for Shockley-Read-Hall-type recombination.

The origin of the green gap for GaInN/GaN quantum wells is investigated via temperature-dependent time-resolved photoluminescence spectroscopy. A strong correlation between nonradiative lifetimes and total strain energy is observed, although the wells are almost fully strained. We discuss this observation in terms of nonradiative recombination at defects which contribute to a beginning partial relaxation. The formation energy of a defect is likely reduced by the amount of its released strain energy. We therefore expect an exponential dependence of the defect density on this released strain energy. Our measured nonradiative lifetimes are consistent with a cumulative strain driven generation of defects.

A strong enhancement of Eu3+ luminescence in europium-implanted GaN samples is obtained by codoping with silicon (Si) and magnesium (Mg), simultaneously. The Eu3+ intensity in the 5D0 to 7F2 transition region is found to be 30 times higher compared to europium-implanted undoped GaN. The major contribution to this overall enhancement is due a weak peak present only in europium-implanted Mg-doped GaN at 2.0031 eV (618.9 nm) which is strongly enhanced by codoping both Mg and Si. The excitation process of europium ions is proposed to take place through a donor-acceptor pair related energy transfer mechanism.

We investigated the optical polarization anisotropy of m-plane GaInN/GaN quantum well structures on m-plane SiC and bulk GaN substrates. On bulk GaN, the degree of polarization increases with increasing indium content according to the larger strain-induced separation of the topmost valence bands. On m-plane SiC, however, we observe constantly large polarization ratios of around 90% and more. From an x-ray strain state analysis and calculations of the valence band energies, we find that an anisotropic strain of the GaN buffer layer leads to a very strong separation of the topmost valence bands resulting in a large degree of polarization.

We have studied the growth of GaInN/GaN quantum wells on various polar, nonpolar and semipolar planes. From a detailed x-ray diffraction analysis, we derive the strain state and the composition of the quantum wells. The optical emission energy is obtained from photoluminescence spectra and modelled taking into account the deformation potentials and the Stark shifts. Both x-ray and optical data consistently show that indium incorporation is identical on the polar, nonpolar and semipolar planes within the experimental uncertainty.

The latencies of the acoustically evoked brainstem potentials depend on brainstem temperature. The sensitivity of this method in detecting changes of temperature is 0.4°C. It was used to see whether face fanning or scalp cooling in hyperthermic human subjects dissociate brainstem temperature from general core temperature. No such evidence was found. It is concluded that external cooling does not decrease brainstem temperature significantly below that of the rest of the body core.

We compare radiative and nonradiative recombination in polar and nonpolar GaInN/GaN quantum wells and demonstrate that purely radiative recombination can be achieved even at room temperature. The radiative recombination is due to free excitons, which partially dissociate at elevated temperatures. Nonradiative recombination is strongly inhibited in the polar case but not in the nonpolar case.