A high-performance flip-chip light-emitting diode (FCLED) with a Ni/Ag metallic film as high reflectivity mirror (92.67%) of p-type electrode was successfully fabricated. The effect of geometric electrode patterns on the blue InGaN/GaN LEDs was investigated and analyzed qualitatively its current spreading in the active region. With different electrode patterns, these devices were experimented and simulated by simple electrical circuits in order to confirm its current-voltage characteristics and light emission pattern. It was found that the forward voltages of these FCLEDs were about 3.6 V (@350 mA). The light output power of FCLEDs with circle-round type electrode was 368 mW at an injection current of 700 mA. From these optoelectronic measurement and thermal infrared images, we proposed some design methodologies for improved current spreading, light output power, droop efficiency and thermal performance.

A high-quality GaN-based vertical light-emitting diode (LED) was successfully fabricated and transferred to an electroplated Cu substrate using strip-patterned silicon dioxide (SiO2) as a sacrificial layer in a chemical lift-off (CLO) process. The SiO2 strip patterns not only provide the sacrificial structure during the detachment process, but also improve the quality of GaN epilayers through epitaxial lateral overgrowth. Compared with conventional LEDs, the CLO-LEDs have a higher output power and a lower forward voltage. The CLO-LED has a decrease in forward voltage of 0.42 V (at 20 mA) as compared with the conventional LED. In addition, at a drive current of 350 mA, the output power of CLO-LEDs is enhanced ~ 2.2 fold, compared with that of conventional LEDs

No abstract

In this study, GaN-based blue light-emitting diodes (LEDs) with an electron retarded layer (ERL) were investigated and demonstrated. The external quantum efficiency (EQE) and efficiency droop effect can be effectively improved by introducing the ERL which was attributed to the retard of the electrons rejected into the multiple quantum wells (MQWs). Therefore, the electron overflow effect can be effectively suppressed and carrier distribution can become more uniform in the MQWs. Regarding the thermal effect, the hot-cold factors of LEDs with ERL can achieve a better performance due to the carrier uniform distribution in the MQWs, which is not easily influenced by the temperature. On the other hand, the temperature dependence of the electroluminescence (EL) of LEDs with ERL also can exhibit a better property especially at lower temperature. Index Terms-GaN-based, LEDs, electron retarded layer, efficiency droop, electron overflow1551-319X (c)

Recently, near-ultraviolet light-emitting diodes (NUV-LEDs) have been used in many applications such as light sources for ultraviolet curing, environmental cleaning, biomedical instrumentation, counterfeit bill detection and phosphor-based white LEDs. However, it is difficult to fabricate NUV-LEDs with high emission efficiency. As the wavelength of NUVLEDs decreases, the most dominant emission will be photons with transverse-magnetic (TM) polarization. For LED structures grown on a c-plane substrate, TM-light propagates mainly in the lateral direction, and it suffers strong effects of total internal reflection (TIR) due to the large incident angle on the interface. Therefore, light extraction efficiency (LEE) of NUV-LEDs is still lower than that of visible LEDs. In this study, a spin coating process in which the grating structure comprises the metallic nanoparticle layer coated on a p-GaN top layer was developed. Various sizes of metallic nanoparticles forming a suspended nanoparticle layer (SNL) embedded in a transparent conductive layer were clearly observed after the deposition of indium tin oxide (ITO). The SNL enhanced the light extraction efficiency of NUVLEDs. Light output power was 1.4 times the magnitude of that of conventional NUV-LEDs operating at 350 mA, but retained nearly the same current-voltage characteristic. Unlike in previous research on surface-plasmon-enhanced LEDs, the metallic nanoparticles were consistently distributed over the surface area. Device performance can be improved substantially by using the three-dimensional distribution of metallic nanoparticles in the SNL, which scatters the propagating light randomly and is coupled between the localized surface plasmon and incident light internally trapped in the LED structure through TIR.Keywords: Surface plasmon, nanoparticle, light-emitting diode (LED), internal quantum efficiency (IQE), external quantum efficiency (EQE), light extraction efficiency (LEE), electroluminescence spectrum, metal-organic chemical vapor deposition (MOCVD), localized surface plasmons (LSPs), transparent conductive layer.