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The influence of hydrogen rate on optical properties of silicon nanocrystals deposited by sputtering method was studied by means of time-resolved photoluminescence spectroscopy as well as transmission and reflection measurements. It was found that photoluminescence decay is strongly non-single exponential and can be described by the stretched exponential function. It was also shown that effective decay rate probability density function may be recovered by means of Stehfest algorithm. Moreover, it was proposed that the observed broadening of obtained decay rate distributions reflects the disorder in the samples.

In this work, we show the results of low-temperature photoluminescence (PL), time-resolved photoluminescence, and photoreflectance (PR) investigations, performed on a series of three Ga 0.64 In 0.34 As 1− x N x /GaAs single quantum wells (SQW) grown by metalorganic vapor phase epitaxy with the nitrogen content of 0, 0.5, and 0.8 %. Comparing the PL and PR data, we show that at low excitation intensity and temperature, the radiative recombination occurs via localizing centers (LCs) in all samples. The excitation intensity-dependent PL measurements combined with theoretical modeling of hopping excitons in this system allow us to provide quantitative information on the disorder parameters describing population of LCs. It has been found that the average energy of LCs increases about two times and simultaneously the number of LCs increases about 10 and 20 times after the incorporation of 0.5 and 0.8 % of nitrogen, respectively. The value of average localization energy ɛ 0 determined for N-containing samples (~6–7 meV) is in the range typical for dilute nitride QWs grown by molecular beam epitaxy (MBE). On the other hand, the “effective” concentration of LCs seems to be higher than for GaInNAs/GaAs QW grown by MBE. The dramatic increase in localizing centers also affects the PL dynamics. Observed PL decay time dispersion is much stronger in GaInNAs SQW than in nitrogen-free SQW. The change in PL dynamic is very well reproduced by model of hopping excitons.

It is shown that in polar InGaN QWs emitting in the blue-green spectral region a Stokes shift between spontaneous emission (SE) and optical transition observed in contactless electroreflectance (CER) spectrum (absorption-like technique) can be observed even at room temperature, despite the fact that the SE is not associated with localized states. Time resolved photoluminescence measurements clearly confirm that the SE is strongly localized at low temperatures whereas at room temperature the carrier localization disappears and the SE can be attributed to the fundamental transition in this QW. The Stokes shift is observed in this QW system because of the large built-in electric field, i.e., the CER transition is a superposition of all optical transitions with non-zero electron-hole overlap integrals and, therefore, the energy of this transition does not correspond to the fundamental transition of InGaN QW. Lasing from this QW has been observed at the wavelength of 475 nm, whereas the SE was observed at 500 nm. The 25 nm shift between the lasing and SE is observed because of a screening of the built-in electric field by photogenerated carriers. However, our analysis shows that the built-in electric field inside the InGaN QW region is not fully screened under the lasing conditions.

Background—Eradication ofHelicobacter pylori cures and prevents the relapse of duodenal ulceration and also results in histological resolution of chronic active gastritis. Aim—To compare four treatment regimens lasting seven days of a proton pump inhibitor and two antibiotics in the eradication of H pylori. Patients—Men or women with H pylori positive duodenal ulceration or gastritis, or both. Methods—A single blind, prospectively randomised, parallel group, comparative, multicentre study. After a positive CLO test, patients underwent histology, H pylori culture, and a 13C urea breath test to confirm H pyloristatus. Treatment with one of four regimens: LAC, LAM, LCM, or OAM, where L is 30 mg of lansoprazole twice daily, A is 1 g of amoxycillin twice daily, M is 400 mg of metronidazole twice daily, C is 250 mg of clarithromycin twice daily, and O is 20 mg of omeprazole twice daily, was assigned randomly. A follow up breath test was done at least 28 days after completing treatment. Results—H pylori eradication (intention to treat) was 104/121 (86.0%) with LAC, 87/131 (66.4%) with LAM, 103/118 (87.3%) with LCM, and 94/126 (74.6%) with OAM. There was a significant difference (p < 0.001) in the proportion of patients in whom eradication was successful between LAC and LCM when compared with LAM, but no significant difference (p = 0.15) between LAM and OAM. Metronidazole resistance before treatment was identified as a significant prognostic factor with regard to eradication of H pylori. The regimens which contained metronidazole were significantly less effective than those without metronidazole in the presence of pretreatment resistant H pylori. There was no difference among the treatment groups with regard to the incidence and severity of adverse events reported. Conclusions—All four treatment regimens were safe and effective in eradicating H pylori in the patient population studied. LAC was the most efficacious treatment in patients with pretreatment metronidazole resistant H pylori, and was significantly better than LAM and OAM in this group of patients.

The issue of quantum mechanical coupling between a semiconductor quantum dot and a quantum well is studied in two families of GaAs- and InP- based structures at cryogenic temperatures. It is shown that by tuning the quantum well parameters one can strongly disturb the 0D-character of the coupled system ground state, initially located in a dot. The out-coupling of either an electron or a hole state from the quantum dot confining potential is viewed by a significant elongation of the photoluminescence decay time constant. Band structure calculations show that in the GaAs-based coupled system at its ground state a hole remains isolated in the dot, whereas an electron gets delocalized towards the quantum well. The opposite picture is built for the ground state of a coupled system based on InP.

The lateral interdot coupling is investigated in high density (∼10 cm−2 ) self-assembled InAs quantum dots (QDs) grown on an InP substrate. Two types of structures are selected for this study, in which QDs are embedded into an InAlAs matrix, forming nearly twice stronger confinement for an electron and a hole than expected for an InAlGaAs counterpart. Resonantly injected low carrier population in these families of QDs gives very different spectral and temporal response in the temperature range of 5-30 K. While InAs/InAlGaAs QDs show monotonic temperature quench of photoluminescence (PL), the process seems to be ineffective in the family of InAs/InAlAs dots. Moreover, the PL decay traces for InAs/InAlGaAs QDs reveal a two-exponential decay as compared to a mono-exponential one observed for InAs/InAlAs dots. While a short decay component of ≤1.9 ns has been attributed to recombination of an electron-hole pair confined in the dot, the long one of >2.4 ns, observed exclusively for InAs/InGaAlAs QDs, is attributed to recombination of spatially separated electron-hole pairs formed due to carrier exchange between adjacent dots.

In this work, AlGaAs/GaAs superlattice, with layers’ sequence and compositions imitating the active and injector regions of a quantum cascade laser designed for emission in the terahertz spectral range, was investigated. Three independent absorption-like optical spectroscopy techniques were employed in order to study the band structure of the minibands formed within the conduction band. Photoreflectance measurements provided information about interband transitions in the investigated system. Common transmission spectra revealed, in the target range of intraband transitions, mainly a number of lines associated with the phonon-related processes, including two-phonon absorption. In contrast, differential transmittance realized by means of Fourier-transform spectroscopy was utilized to probe the confined states of the conduction band. The obtained energy separation between the second and third confined electron levels, expected to be predominantly contributing to the lasing, was found to be ~9 meV. The optical spectroscopy measurements were supported by numerical calculations performed in the effective mass approximation and XRD measurements for layers’ width verification. The calculated energy spacings are in a good agreement with the experimental values.

Here we present optical spectroscopy studies to examine structural and optical properties of active region of quantum cascade lasers grown fully by MOCVD technique. The active part is InGaAs/AlInAs based multilayer structure nominally lattice matched to InP substrate. In this communication we study a set of structures with different growth temperature of the cladding layers and its influence on the properties of active core. The x-ray spectroscopy (XRD) allowed to determine the widths of constituent layers and compare obtained values with nominal ones. Fourier-transformed photoluminescence (FTPL) and photoreflectance (PR) measurements provided high signal to noise spectra, proving good optical and structural properties of investigated samples. A model of atoms interdiffusion processes was presented to explain observed small energy shifts of the transitions energies within the investigated multilayer structures.

Kendall (Foundations of a theory of random sets, in Harding, E.F., Kendall, D.G. (eds.), pp. 322–376, Willey, New York, 1974) showed that the operation \\(_1 P_+^2 P_+\\) given by \\[_x_1_1=x_2+(1-x)_1,\\] where x∈[0,1] and πβ is the Pareto distribution with the density function βs−β−1 on the set [1,∞), defines a generalized convolution on ℘+. Kucharczak and Urbanik (Quasi-stable functions, Bull. Pol. Acad. Sci., Math. 22(3):263–268, 1974) noticed that also the following operation \\[_x__1=x^_2+(1-x^)_1\\] defines generalized convolutions on ℘+. In this paper, we show that ⋄α convolutions are the only possible convolutions defined by the convex linear combination of two fixed measures. To be precise, we show that if ⋄:℘2→℘ is a generalized convolution defined by \\[_x _1=p(x)_1+(1-p(x))_2,\\] for some fixed probability measures λ1,λ2 and some continuous function p:[0,1]→[0,1], p(0)=0=1−p(1), then there exists an α>0 such that p(x)=xα, ⋄=⋄α, λ1=π2α and λ2=δ1. We present a similar result also for the corresponding weak generalized convolution.

Electromodulation spectroscopy (photoreflectance and electroreflectance) is an excellent technique to study optical transitions in quantum well (QW) structures but the development of this technique in the midinfrared spectral region is still limited due to various reasons. In this work we report our recent progress in the development of contactless electroreflectance spectroscopy in midinfrared and discuss some aspects and perspectives of this technique in the context of its application to study optical transitions in GaSb-based QWs. Especially, we have focused on the band offset issue in GaInAsSb/GaSb QWs since the accurate study/verification of band gap discontinuities at QW interfaces is a crucial point in the optimization of laser structures grown on GaSb substrate and operating in the 1.8–3.0 μm spectral range.