Aggravated efficiency droop in vertical-structured gallium nitride light-emitting diodes induced by high temperature aging

Abstract

The present work demonstrates that aging at higher temperatures significantly aggravates “efficiency droop” in the n-side-up vertical-structured GaN-based light-emitting diodes (LEDs). The observed luminous efficiency droop is over 40% at the measuring current of 350 mA. This phenomenon closely relates with creeping of Au80Sn20 eutectic bonds. On one hand, the plastic deformation accumulated during creeping at higher aging temperatures will make the LED epilayers tensile strained at room temperature. The tensile strain induces a change of the internal quantum efficiency (IQE). The maximum variation of IQE related with strain states was around 20%. On the other hand, creeping under the thermal-mismatching induced tensile stress activates voids' nucleation and growth in the solder bonds. The distribution profile of voids in solder bonds will be mapped on the multiple quantum-well structure in vertical-structured LED chips. Local current densities can be much higher than the average current density used in the calculation of LED's efficiencies. Therefore, the efficiency roll-off value will shift toward the smaller bias direction and the total internal quantum efficiency will decrease as current increases.

Efficiency Boosting by Thermal Harvesting in InGaN/GaN Light-Emitting Diodes

“…However, high self-heating and low heat dissipation are the critical issues needed to be addressed during the operation of LEDs. Therefore, extensive research and development efforts have been devoted to reducing the thermal heat generated in the InGaN/GaN-based LEDs to reduce the thermal droop, which rapidly drops the device efficiency under a high input electrical power especially in the high voltage regime(qV > Zω) [11][12][13][14][15][16][17][18]. Over the past couple of decades, plenty of architectures and solutions have been proposed to address the scientific and technological challenges introduced by the thermal heat, including adding the heat sink, increasing the heat dissipation area, changing n-electrode length, and exploiting the thermoelectric generator [19][20][21][22][23].…”

Multi-Azimuth Failure Mechanisms in Phosphor-Coated White LEDs by Current Aging Stresses

“…Thirty samples are divided into three groups (each group contains 10 samples) corresponding to three aging conditions. After aging tests, all samples are cooled down in the air for more than 5 h to release the remaining thermal energy prior to following measurements [25]. All instruments used in the experimental study are listed in Table 1.…”