To improve heat dissipation of sapphire-based LEDs, we develop a new LED package with a dual heat spreader design. The first heat spreader is a cup-shaped copper sheet, which was directly contacted with sapphire to enhance heat dissipation of the chip itself. The second heat spreader is the die-bonding material of diamond-added AgSnCu solder and a high thermal conductive metal-core printed circuit board (MCPCB), where the conventional dielectric layer was replaced with a thin diamond-like layer. Characterization results demonstrate that the diamond-added composite solder is useful in reducing LED thermal resistance, thus avoiding the thermal accumulation phenomenon. In addition, a LED packaged on the new MCPCB exhibits smaller total thermal resistance and larger light output power

We report on improved device performance of flip-chip (FC) GaN-based light-emitting diodes (LEDs) by combining patterned sapphire substrate (PSS) and thin-film techniques. It was found that an FC LED grown on a conventional planar sapphire exhibits a power enhancement factor of only 36.3% after the thin-film processes of substrate removal and surface roughening. In contrast, the as-fabricated FC LED grown on a PSS showed a power enhancement factor of up to 62.3% without any postprocess as compared with the light output power of an original conventional FC LED. Further intensity improvement to 74.4% could be achieved for the FC LED/PSS sample with the thin-film processes

In this letter, we report on the fabrication and photovoltaic characteristics of p-i-n GaN/InGaN thin-film solar cells. The thin-film solar cells were fabricated by removing sapphire using a laser lift-off technique and, then, transferring the remaining p-i-n structure onto a Ti/Ag mirror-coated Si substrate via wafer bonding. The mirror structure is helpful to enhance light absorption for a solar cell with a thin absorption layer. After the thin-film process for a conventional sapphire-based p-i-n solar cell, the device exhibits an enhancement factor of 57.6% in current density and an increment in conversion efficiency from 0.55% to 0.80%. The physical origin for the photocurrent enhancement in the thin-film solar cell is related to multireflection of light by the mirror structure

This letter presents performance comparison between a GaAs/mirror/copper thin-film solar cell and a conventional GaAs solar cell with a thick GaAs substrate. The GaAs thin-film solar cell was fabricated by transferring a GaAs solar cell onto a AuGe/Au mirror-coated copper substrate. With the aid of the excellent copper conductor, the thin-film solar cell exhibits significant improvement in both open-circuit voltage and short circuit current density. The improved current-voltage (I-V) performance of the thin-film solar cell originates from the following two factors: reduced reverse saturation current by good heat dissipation of copper and enhanced light absorption by the highly reflective AuGe/Au mirror. The role of the mirror can further be verified in the measurement of external quantum efficiency (EQE) response where the thin-film solar cell exhibits a larger EQE response in the wavelength range of 700-900 nm than the conventional GaAs solar cell with the same active absorbing thickness

Blue InGaN LEDs with periodically surface-textured indium tin oxide by holographic lithography were compared with those textured randomly by natural lithography where polystyrene spheres (PSs) with required diameter were employed as a mask for dry-etching process. It was found that the employed texturing processes not only exhibit unchanged I-V characteristics but also improve light output power. The turn-ON threshold voltages of all the textured InGaN LEDs are similar to that of a conventional LED chip. An LED textured with a regular pattern with 600 nm pitch exhibits a maximum power enhancement of 65.2% at an injection current of 350 mA as compared with that of an original one. In addition, the LEDs with this 600 nm array pattern present much better light extraction than that textured with equal dimensioned PSs, which is indicative of the superior diffraction-dominated light extraction behavior