The exciton localization (ELZ) in polar (0001) and semipolar (112̅ 2) In 0.2 Ga N 0.8 multiplequantum-well (MQW) structures has been studied by excitation power density and temperature dependent photoluminescence. The ELZ in the (112̅ 2) MQW was found to be much stronger (ELZ degree σ E ∼ 40 -70 meV) compared to the (0001) MQW (σ E ∼ 5−11 meV) that was attributed to the anisotropic growth on the (112̅ 2) surface. This strong ELZ was found to cause a blue-shift of the (112̅ 2) MQW exciton emission with rising temperature from 200 to 340 K, irrespective of excitation source used. A lower luminescence efficiency of the (112̅ 2) MQW was attributed to their anisotropic growth, and higher concentrations of unintentional impurities and point defects than the (0001) MQW.

Abstractauthoren InGaN multiple quantum well light‐emitting diodes (LEDs) were grown on chemically–mechanically polished (112―2) GaN templates (up to 100 mm diameter wafers) by metalorganic vapour phase epitaxy. Initial GaN overgrowth on the polished templates in nitrogen ambient maintained the polished surface. The peak emission wavelength of the LEDs varied from 445 to 550 nm. In contrast to the simultaneously grown LEDs on as‐grown templates, the LEDs on polished templates have very smooth surface morphology, uniform luminescence, and higher output power. Fluorescence images of 445 nm LEDs grown on (a) as‐grown and (b) polished (112―2) GaN templates.

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Heteroepitaxial growth of GaN buffer layers on 3C-SiC/(001) Si templates (4°-offcut towards [110]) by metalorganic vapour phase epitaxy has been investigated. High-temperature grown Al 0.5 Ga 0.5 N/AlN interlayers were employed to produce a single (202̅ 3) GaN surface orientation. Specular crack-free GaN layers showed undulations along [11̅ 0] 3C SiC Si -with a root mean square roughness of about 13.5 nm (50 × 50 μm 2 ). The orientation relationship determined by x-ray diffraction (XRD) was found to beSiC/Si . Low-temperature photoluminescence (PL) and XRD measurements showed the presence of basal-plane stacking faults in the layers. PL measurements of (202̅ 3) multiple-quantum-well and light-emitting diode structures showed uniform luminescence at about 500 nm emission wavelength. A small peak shift of about 3 nm was observed in the electroluminescence when the current was increased from 5 to 50 mA (25-250 A cm −2 ).

Abstract-The scattering properties of dielectric waveguides connected in cascade can be obtained by using the generalized scattering matrix concept, together with the generalized telegraphist equations formulism and the modal matching technique. This review aims to show the potential of periodic structures in dielectric waveguides in order to gain control of light in the design of microwave and photonic devices. The new inverted Π dielectric waveguide is presented. Numerical and experimental results of the complex scattering coefficients were obtained at microwave frequencies. At optical frequencies, results for planar waveguide photonic crystals are included and compared with the numerical values from commercial software. In all cases the agreement was excellent. Electromagnetic and photonic band gaps, photonic windows, optical switching, optical resonant microcavities as well as refractive index optical sensors can be achieved by means of dielectric waveguides in cascade.

Abstract-In this work, we demonstrate that the LSM and LSE modes formulation is an excellent theoretical tool for determining the refractive index and thickness of the guiding layer in planar optical waveguides with step refractive index profile. Refractive index of transparent materials capable of being deposited as a solid thin layer on a substrate for confining light can be evaluated very accurately. The method can be applied to analyze and design monomode and multimode optical waveguides, unlike the methods proposed so far, including cutoff wavelength region. This wave model only requires the experimental evaluation of the effective indices of the guided modes. In order to verify the developed formulation, the commercial software Olympios was used for theoretical comparison. Polymeric planar optical waveguides were fabricated and characterized. A prism coupling method and the Metricon system were used for effective indices measurements and to compare the accuracy. The experimental evaluation of the thickness was carried out by profilometry. In all cases a complete agreement was obtained for refractive index and thickness between theory and experiments.

We present a comprehensive study of the emission spectra and electrical characteristics of InGaN/GaN multi-quantum well light-emitting diode (LED) structures under resonant optical pumping and varying electrical bias. A 5 quantum well LED with a thin well (1.5 nm) and a relatively thick barrier (6.6 nm) shows strong bias-dependent properties in the emission spectra, poor photovoltaic carrier escape under forward bias and an increase in effective resistance when compared with a 10 quantum well LED with a thin (4 nm) barrier. These properties are due to a strong piezoelectric field in the well and associated reduced field in the thicker barrier. We compare the voltage ideality factors for the LEDs under electrical injection, light emission with current, photovoltaic mode (PV) and photoluminescence (PL) emission. The PV and PL methods provide similar values for the ideality which are lower than for the resistance-limited electrical method. Under optical pumping the presence of an n-type InGaN underlayer in a commercial LED sample is shown to act as a second photovoltaic source reducing the photovoltage and the extracted ideality factor to less than 1. The use of photovoltaic measurements together with bias-dependent spectrally resolved luminescence is a powerful method to provide valuable insights into the dynamics of GaN LEDs.

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