Optimized design on high-power GaN-based Micro-LEDs - art. no. 684108

The structure of micro-LEDs was optimized designed. Optical, electrical and thermal characteristics of micro-LEDs were improved. The optimized design make micro-LEDs suitable for high-power device. The light extraction efficiency of micro-LEDs was analyzed by the means of ray tracing. The results shows that increasing the inclination angle of sidewall and height of mesa, and reducing the absorption of p and n electrode can enhance the light extraction efficiency of micro-LEDs. Furthermore, the total light output power can be boosted by increasing the density of micro-structures on the device. The high-power flip-chip micro-LEDs were fabricated, which has higher quantum efficiency than conventional BALED's. When the number of microstructure in micro-LEDs was increased by 57%, the light output power was enhanced 24%. Light output power is 82.88mW at the current of 350mA and saturation current is up to 800mA, all of these are better than BALED which was fabricated in the same epitaxial wafer. The IN characteristics of micro-LEDs are almost identical to BALED.

The effects of sapphire substrates processes to the LED efficiency - art. no. 68410M

We investigate the relation between the thickness of sapphire substrates and the extraction efficiency of LED. The increasing about 5% was observed in the simulations and experiments when the sapphire thickness changed from 100um to 200um. But the output power increasing is inconspicuous when the thickness is more than 200um. The structure on bottom face of sapphire substrates can enhance the extraction efficiency of GaN-based LED, too. The difference of output power between the flip-chip LED with smooth bottom surface and the LED with roughness bottom surface is about 50%, where only a common sapphire grinding process is used. But for those LEDs grown on patterned sapphire substrate the difference is only about 10%. Another kind of periodic pattern on the bottom of sapphire is fabricated by the dry etch method, and the output of the back-etched LEDs is improved about 50% than a common. case.

Plasma induced damage in GaN-based light emitting diodes - art. no. 68410X

The effects of plasma induced damage in different conditions of ICP and PECVD processes on LEDs were presented. For ICP mesa etch, in an effort to confirm the effects of dry etch damage on the optical properties of p-type GaN, a photoluminescence (PL) measurement was investigated with different rf chuck power. It was founded the PL intensity of the peak decreased with increasing DC bias and the intensity of sample etched at a higher DC bias of -400V is less by two orders of magnitude than that of the as-grown sample. Meanwhile, In the IN curve for the etched samples with different DC biases, the reverse leakage current of higher DC bias sample was obviously degraded than the lower one. In addition, plasma induced damage was also inevitable during the deposition of etch masks and surface passivation films by PECVD. The PL intensity of samples deposited with different powers sharply decreased when the power was excessive. The PL spectra of samples deposited under the fixed condition with the different processing time were measured, indicating the intensity of sample deposited with a lower power did not obviously vary after a long time deposition. A two-layer film was made in order to improve the compactness of sparse dielectric film deposited with a lower power.

Combined transparent electrodes for high power GaN-based LEDs with long life time

In this paper fabrication of high power light emitting diodes (LEDs) with combined transparent electrodes on both P-GaN and N-GaN have been demonstrated. Simulation and experimental results show that comparing with traditional metal N electrodes the efficacy of LEDs with transparent N electrode is increased by more than 10% and it is easier in process than the other techniques. Further more, combining the transparent electrodes with dielectric anti-reflection film, the extraction efficiency can be improved by 5%. At the same time, the transparent electrodes were protected by the dielectric film and the reliability of LEDs can be improved.

Multi-wafer 3C-SiC heteroepitaxial growth on Si(100) substrates

Epitaxial growth of semiconductor films in multiple-wafer mode is under vigorous development in order to improve yield output to meet the industry increasing demands. Here we report on results of the heteroepitaxial growth of multi-wafer 3C-SiC films on Si(100) substrates by employing a home-made horizontal hot wall low pressure chemical vapour deposition (HWLPCVD) system which was designed to be have a high-throughput, multi-wafer (3x2-inch) capacity. 3C-SiC film properties of the intra-wafer and the wafer-to-wafer including crystalline morphologies, structures and electronics are characterized systematically. The undoped and the moderate NH3 doped n-type 3C-SiC films with specular surface are grown in the HWLPCVD, thereafter uniformities of intra-wafer thickness and sheet resistance of the 3C-SiC films are obtained to be 6%similar to 7% and 6.7%similar to 8%, respectively, and within a run, the deviations of wafer-to-wafer thickness and sheet resistance are less than 1% and 0.8%, respectively.

Hydrate dissociation conditions for gas mixtures containing carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons using SAFT

A new method, a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate dissociation conditions for binary gas mixtures with carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons in the presence of aqueous solutions. The statistical associating fluid theory (SAFT) equation of state is employed to characterize the vapor and liquid phases and the statistical model of van der Waals and Platteeuw for the hydrate phase. The predictions of the proposed model were found to be in satisfactory to excellent agreement with the experimental data.

Interactions of three dual-dressing effects of four-wave mixing in a five-level atomic system

We study the four-wave mixing (FWM) in an opening five-level system with two dressing fields. There are three kinds of doubly dressing mechanisms (parallel cascade, sequential cascade, and nested cascade) in the system for doubly dressed four-wave mixing. These mechanisms reflect different correlations between two dressing fields and different effects of two dressing fields to the FWM. Investigation of these mechanisms is helpful to understand the generated high-order nonlinear optical signal dressed by multi-fields.

Theoretical design or single-polarization single-mode microstructured polymer optical fibres

Using the full-vector plane-wave expansion method, a kind of PMMA-based polarization-maintaining microstructured optical fibre (PM-mPOF) is theoretically studied. Dependence of the cutoff wavelengths of the two orthogonal polarization states (polarized along the two principal axes of PM-mPOF) on the structure parameters of the fibre is investigated in detail. A single-polarization single-mode (SPSM) PM-mPOF working in the visible region is designed and optimized with the result of the maximum SPSM bandwidth of 140 nm.

Experimental study on K alpha X-ray emission from intense femtosecond laser-solid interactions

The characteristics of K alpha X-ray sources generated by p-polarized femtosecond laser-solid interactions are experimentally studied in the relativistic regime. By use of knife-edge image technique and a single-photon-counting X-ray CCD camera, we obtaine the source size, the spectrum and the conversion efficiency of the Ka X-ray sources. The experimental results show that the conversion efficiency of Ka photons reaches an optimum value of 7.08 x 10(-6)/sr at the laser intensity of 1.6 x 10(18) W/cm(2), which is different from the Reich's simulation results (Reich et al., 2000 Phys. Rev. Lett. 84 4846). We find that about 10% of laser energy is converted into the forward hot electrons at the laser intensity of 1.6 x 10(18) W/cm(2).

Optimization of multiple filamentation of femtosecond laser pulses in air using a pinhole

The robustness and prolongation of multiple filamentation (MF) for femtosecond laser propagation in air are investigated experimentally and numerically. It is shown that the number, pattern, propagation distance, and spatial stability of MF can be controlled by a variable-aperture on-axis pinhole. The random MF pattern can be optimized to a deterministic pattern. In our numerical simulations, we configured double filaments to principlly simulate the experimental MF interactions. It is experimentally and numerically demonstrated that the pinhole can reduce the modulational instability of MF and is favorable for a more stable MF evolution. (c) 2007 Optical Society of America.

Polarization properties of elliptical core non-hexagonal symmetry polymer photonic crystal fibre

In this paper, polarization properties and propagation characteristics of polymer photonic crystal fibres with elliptical core and non-hexagonal symmetry structure are investigated by using the full vectorial plane wave method. The results how that the birefringence of the fibreis induced by asymmetries of both the cladding and the core. Moreover, by adjusting the non-symmetrical ratio factor of cladding eta from 0.4 to 1 in step 0.1, we find the optimized design parameters f the fibre with high birefringence and limited polarization mode dispersion, operating in a single mode regime at an appropriate wavelength range. The range of wavelength approaches the visible and near-infrared which is consistent with the communication windows of polymer optical fibres.

Dynamics of Incoherent Photovoltaic Spatial Solitons

Propagation properties of bright and dark incoherent beams are numerically studied in photovoltaic-photorefractive crystal by using coherent density approach for the first time. Numerical simulations not only exhibit that bright incoherent photovoltaic quasi-soliton, grey-like incoherent photovoltaic soliton, incoherent soliton doublet and triplet can be established under proper conditions, but also display that the spatial coherence properties of these incoherent beams can be significantly affected during propagation by the photovoltaic field.

Dark incoherent spatial solitons in logarithmically saturable nonlinear media

This paper studies numerically the dark incoherent spatial solitons propagating in logarithmically saturable nonlinear media by using a coherent density approach and a split-step Fourier approach for the first time. Under odd and even initial conditions, a soliton triplet and a doublet are obtained respectively for given parameters. Simultaneously, coherence properties associated with the soliton triplet and doublet are discussed. In addition, if the values of the parameters are properly chosen, five and four splittings from the input dark incoherent spatial solitons can also form. Lastly, the grayness of the soliton triplet and that of the doublet are studied, in detail.