Defective silica sphere arrays having locally hexagonal-closed-packed structure but lack of long range ordering were incorporated into organic light emitting diodes as grating to extract the waveguided light trapped in the indium tin oxide/organic layers and the glass substrate. Using these defective hexagonal-closed-packed gratings for light extraction, broad band lambertian emitters are obtained due to the periodicity broadening and the random orientation in the gratings, resulting in enhancements in current and power effi ciencies by a factor of 1.7 and 1.9, respectively.

Articles you may be interested inCarrier recombination mechanisms in nitride single quantum well light-emitting diodes revealed by photo-and electroluminescence J. Appl. Phys.

The band structure of dilute-As GaNAs alloy with the As composition range from 0% to 12.5% is studied by using First-Principle density-functional calculation. Our analysis shows that the dilute-As GaNAs alloy exhibits the direct band gap properties. The dilute-As GaNAs alloy shows a band gap range from 3.645 eV down to 2.232 eV with As content varying from 0% to 12.5%, which covers the blue and green spectral regime. This finding indicates the alloy as a potential candidate for photonic devices applications. The bowing parameter of 14.5 eV 0.5 eV is also obtained using line fitting with the First-Principle and experimental data. The effective masses for electrons and holes in dilute-As GaNAs alloy, as well as the split-off energy parameters, were also presented. Minimal interband Auger recombination is also suggested for the dilute-As GaNAs alloy attributing to the off-resonance condition for this process.

Single metal site catalysts are the most promising candidates to replace platinum-group-metal (PGM) catalysts for the oxygen reduction reaction (ORR), yet insufficient performance and scalable preparation approaches remain great challenges. Here, we report a nitrogen (N)/sulfur (S) codoped single Fe site catalyst (Fe–N/S–C) through a chemical vapor deposition (CVD) strategy. Using the cyclopentadiene-shielded Fe atom ferrocene (Fc) as the precursor, atomically dispersed single Fe sites were successfully embedded into the N, S codoped 2D carbon nanosheets. The superior catalytic activity for the ORR in alkaline media is stemmed from the N, S codoping, tuning the optimal charge distribution of Fe sites. In addition, the CVD approach could surpress the formation of iron-carbide-containing iron clusters (“Fe x C/Fe”), thereby leading to high surface areas and porosity. Furthermore, the Fe–N/S–C catalyst was further studied as a cathode catalyst in direct methanol fuel cells showing encouraging performance.

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Multimedia streaming applications have stringent Quality-of-Service (QoS) requirements. Typically each packet is associated with a packet delivery deadline. This work models and considers streaming broadcast of stored-video over the downlink of a single cell. We first generalize the existing class of immediately-decodable network coding (IDNC) schemes to take into account the deadline constraints. The performance analysis of IDNC schemes are significantly complicated by the packet deadline constraints (from the application layer) and the immediate-decodability requirement (from the network layer). Despite this difficulty, we prove that for independent channels, the IDNC schemes are asymptotically throughput-optimal subject to the deadline constraints when there are no more than three users and when the video file size is sufficiently large. The deadline-constrained throughput gain of IDNC schemes over non-coding scheme is also explicitly quantified. Numerical results show that IDNC schemes strictly outperform the non-coding scheme not only in the asymptotic regime of large files but also for small files. Our results show that the IDNC schemes do not suffer from the substantial decoding delay that is inherent to existing generation-based network coding protocols.

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Spontaneously-grown, self-aligned AlGaN nanowire ultraviolet light emitting diodes still suffer from low efficiency partially because of the strong surface recombination caused by surface states, i.e., oxidized surface and high density surface states. Several surface passivation methods have been introduced to reduce surface non-radiative recombination by using complex and toxic chemicals. Here, we present an effective method to suppress such undesirable surface recombination of the AlGaN nanowires via diluted potassium hydroxide (KOH) solution; a commonly used chemical process in semiconductor fabrication which is barely used as surface passivation solution in self-assembled nitride-based nanowires. The transmission electron microscopy investigation on the samples reveals almost intact nanowire structures after the passivation process. We demonstrated an approximately 49.7% enhancement in the ultraviolet light output power after 30-s KOH treatment on AlGaN nanowires grown on titanium-coated silicon substrates. We attribute such a remarkable enhancement to the removal of the surface