High power UVB light emitting diodes with optimized n-AlGaN contact layers
A. KnauerTim KolbeJens RaßHyun Kyong ChoCarsten NetzelSylvia HagedornNeysha Lobo‐PlochJan RuschelJohannes GlaabS. EinfeldtM. Weyers
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The influence of the n-AlGaN contact layer thickness and doping profile on the efficiency, operating voltage and lifetime of 310 nm LEDs has been investigated. Increasing the n-contact layer thickness reduces the operation voltage of the LEDs and increases the emission power slightly. Optimizing the n-doping profile yielded enhanced conductivity and reduced operation voltage with a simultaneous output power enhancement of the LEDs. Lifetime measurements have shown that even though the output power of the LEDs was enhanced the lifetimes were not negatively affected. Room temperature photoluminescence indicates a low concentration of point defects in the n-doping region yielding minimum AlGaN resistivity.Photoluminescence excitation
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In this work, we present a detailed investigation of the low temperature emission properties of ZnSeO alloys by means of photoluminescence, micro-photoluminescence, and time-resolved photoluminescence. We show that the low temperature broad photoluminescence spectrum of ZnSeO attributed to the recombination of localized excitons is composed of sharp lines related to individual trapping states. Based on studies of photoluminescence thermal quenching from individual trapping states and photoluminescence dynamics, the mechanism of nonradiative recombination in ZnSeO alloys is discussed. Moreover, an unexpected decrease of the low temperature Stokes shift with increasing oxygen content is observed in contrast to what has been reported for GaAs based highly mismatched alloys. The possible origin of this effect is proposed.
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We examined the change in photoluminescence spectra of porous Si when it is oxidized then deoxidized chemically. After both steps, photoluminescence shifted to higher frequencies and increased in intensity. These shifts to higher frequencies indicate the photoluminescence is a result of the quantum size effect. Moreover, the increase in photoluminescence intensity after oxidation suggests that termination by hydrogen on the porous Si surface does not always play a key role in the photoluminescence mechanism.
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In this work we investigate the excitonic properties of (4-FC6H4C2H4NH3)2PbI4 hybrid organic/inorganic thin films. We first use a standard point-by-point photoluminescence mapping. The maps formed using the photoluminescence intensity, line width, and broadening reveal the presence of structural defects. Using a statistical treatment of the data we found that the spatial fluctuations of the photoluminescence peak wavelengths are rather small compared to the photoluminescence line width. Moreover, we report the first direct observation of spatially resolved excitonic photoluminescence in this type of materials using dark-field imaging of white-light pumped photoluminescence. Owing to the rapid acquisition time of the dark-field images, their temperature dependence was studied, and the thermal behavior of the photoluminescence was investigated using this technique. We show that photoluminescence mapping combined with dark-field imaging and spectroscopy provides valuable information on the excitonic properties of hybrid organic/inorganic thin films.
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Abstract Simultaneous measurement of photoluminescence intensity and photoluminescence decay time of porous silicon was used for optical detection of chemical species in gas phase. For the studied set of analytes we observed that quenching of photoluminescence intensity and shortening of photoluminescence decay time scale with the analyte concentration. Simultaneous acquisition of photoluminescence intensity and photoluminescence decay time enabled to improve reliability of the sensor response measurements. Different sensor sensitivity of photoluminescence intensity and decay time to the presence of chemical species makes possible to discriminate between various classes of organic molecules. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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Blue photoluminescence is observed in aged porous silicon samples anodized under Ar+ 488 nm laser illumination. No samples have been undergone any heating treatment process. Both nanosecond and microsecond decay of blue photoluminescence have been measured. Samples show a good monoexponential microsecond decay with lifetimes of about 5.3 μs. Photoluminescence excitation spectra of blue and red Photoluminescence indicate there is a large Stokes shift (about 800-900 meV) in the excitation spectra of red photoluminescence while no this marked Stokes shift in that of blue photoluminescence. The possible origin of the photoluminescence is discussed based on the experimental results.
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