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The reliability of high-power light-emitting-diode (LED) devices strongly depends on the die-attach quality because voids may increase junction temperature and total thermal resistance of LED devices. Die-attach material has a key role in the thermal management of high-power LED package by providing low-contact thermal resistance. Thermal and mechanical analyses were carried out by experiments and thermal simulation. The quantitative analysis results show that thermal resistance of die-attach layer (thermal resistance caused by die-attach material and voids in die-attach layer) plays an important role in total thermal resistance of high-power LED packaging according to the differential structure function of thermal transient characteristics. The increase of void fraction in die-attach layer causes the increases of thermal resistance of die-attach layer; the thermal resistance increased by 1.95 K/W when the void fraction increased to 62.45%. The voids also make an obvious influence on thermal stress and thermal strain of chip; the biggest thermal stress of chip was as high as 847.1 MPa compared to the 565.2 MPa when the void fraction increases from being void-free to 30% in the die-attach layer.

In this work, the high power GaN-based unpackaged chip was drive with high current of 600 mA and high temperature of 130 °C till failure. A large stain area was found in the main light area of die after degradation and the leakage current increased by tiny range. And the illuminance degraded greatly as shown in distribution map. In the meantime, the temperature rose dramatically. FIB, SEM and TEM characterization demonstrated that the detachment between multilayer metal electrodes was the main cause of the stain area and the degradation of illuminance and temperature, and also the higher junction temperature played a key role in this detachment phenomenon.

Carbon quantum dots (CQDs) have attracted much attention owing to their unique optical properties and a wide range of applications. The fabrication and control of CQDs with organic solubility and long-wavelength emission are still urgent issues to be addressed for their practical use in LEDs. Here, organic-soluble CQDs were produced at a high yield of ∼90% by a facile solvent engineering treatment of 1,3,6-trinitropyrene, which were simultaneously used as the nitrogen and carbon sources. The optical properties of the organic-soluble CQDs (o-CQDs) were investigated in nonpolar and polar solvents, films, and LED devices. The CQDs have a narrow size distribution around 2.66 nm, and can be dispersed in different organic solvents. Significantly, the as-prepared CQDs present an excitation-independent emission at 607 nm with fluorescence quantum yields (QYs) up to 65.93% in toluene solution. A pronounced solvent effect was observed and their strong absorption bands can be tuned in the whole visible region (400–750 nm) by changing the solvent. The CQDs in various solvents can emit bright, excitation-independent, long-wavelength fluorescence (orange to red). Furthermore, benefiting from the unique oil-solution properties, the as-prepared CQDs can be processed in thin film and device forms to meet the requirements of various applications, such as phosphor-based white-light LEDs. The color coordinate for these CQD modified LEDs is realized at (0.32, 0.31), which is close to pure white light (0.33, 0.33).

In this paper, the degradation of bare high power GaN/InGaN blue light-emitting diodes (HP-LEDs) was investigated by considering the electrical, thermal and optical aging characteristics. The HP-LED samples were stressed at the elevated temperature of 85 °C with an injection current of 500 mA. The rated current of the HP-LEDs is 350 mA at room temperature. Changing in tunneling current for the electrical characteristic, a gradual increase for the external quantum efficiency (EQE), a gradual decrease for the light power and the luminous flux were monitored. The luminous intensity distribution is more uneven after degradation. And thermal resistance and temperature rise of chip increase with aging time. In addition, the thermal resistance of the die-attach and ceramic wafer were also increasing after aging. After theoretical calculation, the defect concentration of the die monotonously increases with aging time. Therefore, the responsible factors of these changes were proposed to be the generation of the dopant activation, point defects, dislocations and other defects in the chip level during highly accelerated test. These defects as non-radiative recombination centers make charge carrier cross quantum well structure directly. Thereby, the degradation of the electrical, thermal and optical aging characteristics of HP-LEDs is observed.

In this paper, we simulate graphene on the surface of substrate, using interconnection metallization to connect merge pin schottky (MPS) power diode chip and substrate, then build a thermal model of the device, and perform the finite-element analysis with ANSYS software. In recent years, graphene has attracted a large amount of interest because of its outstanding electric conductivity, ultrahigh thermal conductivity and large specific surface area. Therefore, if graphene films are used as heat sink, heat will diffuse through graphene surface at breakneck speeds, solving the heat accumulation problem of the device. In this work, we simulate the heat dissipation effect of the device with graphene films or without graphene films. Then, we change the thickness of graphene films, contact area between graphene films and heat dissipation substrate, and contact area between interconnection metallization and graphene films.

The influence of different degrees of high reverse-bias stress on high power light-emitting diodes (LEDs) was investigated based on the aging of LED devices under the stress of 85 °C / 85 % RH. GaN-based blue LEDs were respectively tested by negative Human-Body-Mode (HBM) electronic static discharge (ESD) at −1000 V, −2000 V, −3000 V, −4000 V and −5000 V. The electrical performances and optical performances of samples were measured before and after ESD test. The LEDs stressed at −1000 V, −2000 V and −3000 V showed a soft breakdown due to the generation of defect inside the chip and LEDs stressed at −4000V and −5000V showed a thermal breakdown. The thermal breakdown made temperature rise rapidly and formed a melting channel, which caused the damage of the LED. Though the electrical performances and optical performances of LEDs stressed at −1000 V, −2000 V and −3000 V did not show conspicuous degradation, the damage induced by ESD affect the reliability of LEDs.