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This investigation describes the development of a InGaN/GaN light-emitting diode (LED) with textured sidewalls using natural lithography with polystyrene spheres (PSs) as the etching mask and dry etching the epitaxial layers of LEDs to achieve nano-scale textured sidewalls. The LED with textured sidewalls increased the output power of the InGaN-GaN multiple quantum well (MQW) LEDs by a factor of 1.3, indicating that the LED with nano-scale textured sidewalls had larger light extraction efficiency. The wall-plug efficiency of nitride-based LEDs was increased by 30% using textured sidewalls.

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This study reports the development of GaN-based power-chip light-emitting diodes ͑LEDs͒ with sidewall roughness using natural lithography with polystyrene spheres as the etching mask. At an injection current of 350 mA, the LED with sidewall roughness increased the light output intensity of the InGaN/GaN multiple quantum well LEDs by a factor of 1.26, indicating that the LED with sidewall roughness had larger light extraction efficiency. The wall-plug efficiency of GaN-based LED was increased by 26.5% with sidewall roughness. After 1000 h life test, it was found that normalized output power of power-chip LED with sidewall roughness did not show any significant degradation. III-nitride wide bandgap light-emitting diodes ͑LEDs͒ have recently attracted considerable interest due to their various applications, such as traffic signals, back-side lighting in liquid crystal display, and illumination lighting by white light LEDs. 1 However, the external quantum efficiency of GaN-based LEDs is low because the refractive index of the nitride epitaxial layer differs greatly from that of the air. The refractive indexes of GaN and air are 2.5 and 1.0, respectively. Thus, the critical angle at which light generated in the InGaN-GaN active region can escape is approximately ͓ c = sin −1 ͑n air /n GaN ͔͒ ϳ 23°, which limits the external quantum efficiency of conventional GaN-based LEDs to only a few percent. 2,3 The light from LEDs can be enhanced either through the sample surface or through the sidewalls of the power chip. Research into improving the light extraction efficiency ͑external quantum efficiency͒ and brightness in the LEDs Refs. 3-15 has been intense. These processes all allow the photons generated within the LEDs to find the escape cone, by multiply scattering from a rough surface. A similar concept should also be applied to power chip sidewall. In other words, more photons should be able to escape from powerchip LEDs with sidewall roughness as compared to LEDs with conventional power-chip sidewall.By using plasma-enhanced chemical vapor deposition SiO 2 layer as the etching mask, Chang et al. successfully demonstrated a 10% output power enhancement of nitride-based LEDs with m-scale wavelike textured sidewalls. 8 Due to the lithography limits of their instruments, they used a mask with a large period to fabricate m-scale wavelike textured sidewalls. Further enhancement of the light output can be achieved if sidewall roughness can be reduced to the sub-m or nanoscale range. Recently, Horng et al. demonstrated the power enhancement of surface-textured ITO/GaN LEDs using a combination of natural lithography and dry etching techniques. 9 In this paper, GaN-based power-chip LEDs with chip sidewall roughness were fabricated by natural lithography and dry etching techniques to increase the light output efficiency of power chip LED. In addition, the life test result of power chips with sidewall roughness did not show significant degradation in the electrical properties of GaN-based power-chip LEDs.The GaN-based LED samples w...

When we use halftone as the method to adjust the brightness of an LED array, there may be a difference in utilization among the LEDs which may cause a high utilization of a particular one, easily damaging and reducing the life of the array. In this paper we therefore propose a shift method by using different halftone patterns with complement in the LED array to achieve uniform utilization of each LED.