InAlN electron-blocking layers (EBLs) are shown to improve the emission intensity and to mitigate the efficiency droop problem in III-nitride-based visible light-emitting diodes (LEDs). Using an In0.18Al0.82N EBL in blue LEDs, we have achieved a significant improvement in the electroluminescence emission intensity and a mitigated efficiency droop compared to similar LEDs without an EBL or with an Al0.2Ga0.8N EBL. This indicates that an In0.18Al0.82N EBL is more effective in electron confinement and reduces the efficiency droop possibly caused by carrier spill-over than conventional AlGaN EBLs.
We report on the bandgap variation in thin films of B x Ga 1−x N grown on AlN/sapphire substrates using metal-organic vapor phase epitaxy. Optical transmission, photoluminescence, and x-ray diffraction were utilized to characterize the materials' properties of the B x Ga 1−x N films. In contrast to the common expectation for the bandgap variation, which is based on the linear interpolation between the corresponding GaN and BN values, a significant bowing ͑C = 9.2Ϯ 0.5 eV͒ of the bandgap was observed. A decrease in the optical bandgap by 150 meV with respect to that of GaN was measured for the increase in the boron composition from 0% to 1.8%.
Although Escherichia coli can be genetically engineered to degrade environmental toxic organophosphate compounds (OPs) to nontoxic materials, a critical problem in such whole cell systems is limited substrate diffusion. The present work examined whether periplasmic expression of organophosphorus hydrolase (OPH) resulted in better whole cell enzymatic activity compared to standard cytosolic expression. Recombinant OPH periplasmic expression was achieved using the general secretory (sec) pathway with the pelB signal sequence. We found that while total OPH activity in periplasmic-expressing cell lysates was lower compared to that in cytosolic-expressing cell lysates whole cell OPH activity was 1.8-fold greater at 12 h post-induction in the periplasmic-expressing cells as a result of OPH translocation into the periplasmic space ( approximately 67% of whole cell OPH activity was found in the periplasmic fraction). These data suggest that E. coli engineered to periplasmically secrete OPH via the sec pathway may provide an improved whole cell biodegradation system for destruction of environmental toxic OPs.
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