Significant Improvement In Optical Properties Research Articles

Comprehensive optimization of electronic and optical properties of polar III-nitride laser

A detailed investigation is performed to obtain optimized optical performance of polar III-nitride single quantum well (SQW) semiconductor lasers by band engineering through symmetric and asymmetric tuning of device parameters. Electronic, optical, and threshold characteristics are calculated to analyze the effects of band engineering on device performance. Here, the InN-In0.25Ga0.75 N SQW structure is chosen as a case study. This work shows a significant improvement in optical properties from higher wavefunction overlap integral obtained from band modification due to the tuning which also provides higher momentum matrix elements, spontaneous emission rate, and optical gain, as well. The maximum TE-polarized optical gain for the symmetric structure is found as around 6291 cm−1 for 6 A well width and 6 A barrier width at 710 nm, while for asymmetric laser structure, a maximum TE-polarized optical gain of around 6225 cm−1 at around 800 nm is observed for 6 A well width with asymmetric barrier width of 6 A and 8 A. The optimization is carried out over 500–1600 nm wavelength range to obtain the optimum structure for maximum optical performance at different wavelengths. A time-efficient genetic algorithm-based optimization is also performed that provides the same optimization results in reduced time.

Structural, Optical and Microstructural Properties of TiNi Thin Films before and after Oxidation

The deposition of composites with tailored optical properties is investigated. This would employ structures consisting of combined metallic and oxides nature. A thin layer of TiNi is obtained by using RF magnetron sputtering on a stainless-steel substrate, followed by oxidation at 400°C and 800°C for four and one hours, respectively. The optical properties of the thin films were characterized by optical spectrophotometer, and Fourier Transform Infrared Spectroscopy (FTIR). The morphology, topography, and structure were studied by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD). The results show that TiO2 has been produced through the oxidation process of the sputter-deposited TiNi thin film at high oxidation temperature. The TiNi thin films showed a significant improvement in optical properties after oxidation, as the absorbance increased, and the emittance was reduced. This work introduces oxidized TiNi thin films as candidates for solar selective absorber.

XCage: A Tricyclic Octacationic Receptor for Perylene Diimide with Picomolar Affinity in Water

The rational design of wholly synthetic receptors that bind active substrates with ultrahigh affinities is a challenging goal, especially in water. Here, we report the synthesis of a tricyclic octacationic cyclophane, which exhibits complementary stereoelectronic binding toward a widely used fluorescent dye, perylene diimide, with picomolar affinity in water. The ultrahigh binding affinity is sustained by a large and rigid hydrophobic binding surface, which provides a highly favorable enthalpy and a slightly positive entropy of complexation. The receptor-substrate complex shows significant improvement in optical properties, including red-shifted absorption and emission, turn-on fluorescence, and efficient energy transfer. An unusual single-excitation, dual-emission, imaging study of living cells was performed by taking advantage of a large pseudo-Stokes shift, produced by the efficient energy transfer.

Implementation of light extraction improvements of GaN-based light-emitting diodes with specific textured sidewalls

Textured-sidewall GaN-based light-emitting diodes (LEDs) with various sidewall angles (15–90°) and convex or concave sidewalls prepared using an inductively-coupled-plasma approach are comprehensively fabricated and studied. The device with 45° sidewalls (Device F) and that with convex sidewalls (Device B) show significant improvements in optical properties. Experiments show that, at an injection current of 350 mA, the light output power, external quantum efficiency, wall-plug efficiency, and luminous flux of Device F (Device B) are greatly improved by 18.3% (18.2%), 18.2% (18.2%), 17.3% (19.8%), and 16.6% (18.4%), respectively, compared to those of a conventional LED with flat sidewalls. In addition, negligible degradation in electrical properties is found. The enhanced optical performance is mainly attributed to increased light extraction in the horizontal direction due to a significant reduction in total internal reflection at the textured sidewalls. Therefore, the reported specific textured-sidewall structures (Devices B and F) are promising for high-power GaN-based LED applications.

GaAs surface passivation by ultra-thin epitaxial GaP layer and surface As–P exchange

The GaAs surface passivation effects of epitaxially grown ultra-thin GaP layers and surface As–P exchange have been investigated. Optical properties of passivated and unpassivated InGaAs/GaAs near-surface quantum wells (QWs) grown by metal organic vapor phase epitaxy (MOVPE) are studied by low-temperature continuous-wave and time-resolved photoluminescence (PL). By optimizing the growth conditions, smooth surface morphologies and significant improvement of optical properties were observed for both passivation methods. Passivation improved the PL intensity more than two orders of magnitude and notably increased the PL decay time.

MBE growth of InAs self-assembled quantum dots embedded in GaNAs strain-compensating layers

We fabricated self-assembled InAs quantum dots (QDs) embedded with a combined set of a GaNAs strain-compensating layer (SCL) and an InGaAs strain-reducing layer (SRL) by using atomic hydrogen-assisted molecular beam epitaxy (H-MBE) with a RF plasma nitrogen source. By inserting an InGaAs SRL between the InAs QD layer and GaNAs SCL, we were able to achieve a significant improvement of optical properties. A 1.3 μ m -range photoluminescence (PL) emission was clearly obtained at 300 K from QDs embedded in a 5 nm-thick In 0.15Ga 0.85As SRL followed by a 20 nm-thick GaN 0.008As 0.992 SCL. Further, PL emission from the first excited state of QDs was also observed under a high excitation intensity of ∼ 20.0 W / cm 2 .