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.

AlGaN layers grown on AlGaN buffer layer and GaN buffer layer using strain-relief interlayers - art. no. 68410S

We investigated AlGaN layers grown by metalorganic chemical vapor deposition (MOCVD) on high temperature (HT-)GaN and AlGaN buffer layers. On GaN buffer layer, there are a lot of surface cracking because of tensile strain in subsequent AlGaN epilayers. On HT-AlGaN buffer layer, not only cracks but also high densities rounded pits present, which is related to the high density of coalescence boundaries in HT-AlGaN growth process.The insertion of interlayer (IL) between AlGaN and the GaN pseudosubstrate can not only avoid cracking by modifying the strain status of the epilayer structure, but also improved Al incorporation efficiency and lead to phase-separation. And we also found the growth temperature of IL is a critical parameter for crystalline quality of subsequent AlGaN epilayer. Low temperature (LT-) A1N IL lead to a inferior quality in subsequent AlGaN epilayers.

High-brightness GaN-based blue LEDs grown on a wet-patterned sapphire substrate - art. no. 68410T

Patterning sapphire substrate can relax the stress in the nitride epilayer, reduce the threading dislocation density, and significantly improve device performance. In this article, a wet-etching method for sapphire substrate is developed. The effect of substrate surface topographies on the quality of the GaN epilayers and corresponding device performance are investigated. The GaN epilayers grown on the wet-patterned sapphire substrates by MOCVD are characterized by means of scanning electrical microscopy (SEM), atomic force microscopy (AFM), high-resolution x-ray diffraction (HRXRD), and photoluminescence (PL) techniques. In comparison with the planar sapphire substrate, about a 22% increase in device performance with light output power of 13.31 mW@20mA is measured for the InGaN/GaN blue LEDs grown on the wet-patterned sapphire substrate.

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.

Research on color matching of LED backlight for large-color-gamut LCD application - art. no. 68410Y

Comparing with the conventional CCFL (Cold Cathode Fluorescent Lamp) backlight, three-basic-color LEDs backlight has some advantages such as good color reproduction, long life and lead free etc. Theoretically, the color gamut is determined by x, y coordinates of the three basic colors in CIE chromaticity diagram, and the x, y coordinates of each basic color can derived from the relative spectrum distribution (RSD) of the LED. In this paper, the red, green and blue LEDs' RSD models are established to calculate and analyze the color gamut of a backlight. By simulating those models, the relationships that the color gamut of a LED backlight varies with each color are analyzed, and the optimum combination of three colors is obtained within the given wavelengths ranges. Moreover, the combinations of three colors for the gamut of 115% NTSC and 110% NTSC are plotted in pictures, respectively.

Thermal test and analysis of concentrator solar cells - art. no. 684117

Under high concentration the temperature of photovoltaic solar cells is very high. It is well known that the efficiency and performance of photovoltaic solar cells decrease with the increase of temperature. So cooling is indispensable for a concentrator photovoltaic solar cell at high concentration. Usually passive cooling is widely considered in a concentrator system. However, the thermal conduction principle of concentrator solar cells under passive cooling is seldom reported. In this paper, GaInP/GaAs/Ge triple junction solar cells were fabricated using metal organic chemical vapor deposition technique. The thermal conductivity performance of monolithic concentrator GaInP/GaAs/Ge cascade solar cells under 400X concentration with a heat sink were studied by testing the surface and backside temperatures of solar cells. The tested result shows that temperature difference between both sides of the solar cells is about 1K. A theoretical model of the thermal conductivity and thermal resistance of the GaInP/GaAs/Ge triple junction solar cells was built, and the calculation temperature difference between both sides of the solar cells is about 0.724K which is consistent with the result of practical test. Combining the theoretical model and the practical testing with the upper surface temperature of tested 310K, the temperature distribution of the solar cells was researched.

Growth of GaSb and GaInAsSb layers for thermophotovolatic cells by liquid phase epitaxy - art. no. 68411E

GaSb based cells as receivers in thermophotovoltaic system have attracted great interest and been extensively studied in the recent 15 years. Although nowadays the manufacturing technologies have made a great progress, there are still some details need to make a further study. In this paper, undoped and doped GaSb layers were grown on n-GaSb (100) substrates from both Ga-rich and Sb-rich solutions using liquid phase epitaxy (LPE) technique. The nominal segregation coefficients k of intentional doped Zn were 1.4 and 8.8 determined from the two kinds of GaSb epitaxial layers. Additionally, compared with growing from Ga-rich solutions, the growing processes from Sb-rich solutions were much easier to control and the surface morphologies of epitaxial layers were smoother. Further-more, in order to broaden the absorbing edge, Ga1-xInxAsySb1-y quaternary alloys were grown on both GaSb and InAs substrates from In-rich solutions, under different temperature respectively.

Electroabsorption-modulated DFB laser integrated with dual-waveguide spot-size converter - art. no. 60200N

A 1.55-mu m ridge DFB laser and electroabsorption modulator monolithically integrated with a buried-ridge-stripe dual-waveguide spot-size converter at the output port for low-loss coupling to a cleaved single-mode optical fiber was fabricated by means of selective area growth, quantum well intermixing and dual-core technologies. These devices exhibit threshold current of 28 mA, side mode suppression ratio of 38.0 dB, 3-dB modulation bandwidth of 12.0 GHz, modulator extinction ratios of 25.0 dB dc. The output beam divergence angles of the spot-size converter in the horizontal and vertical directions are as small as 8.0 degrees x 12.6 degrees, respectively, resulting in 3.2 dB coupling loss with a cleaved single-mode optical fiber.