Efficiency degradation behaviors of current/thermal co-stressed GaN-based blue light emitting diodes with vertical-structure

Abstract

With this work, we demonstrate a three-stage degradation behavior of GaN based LED chips under current/thermal co-stressing. The three stages in sequence are the initial improvement stage, the platform stage, and the rapid degradation stage, indicating that current/thermal co-stressing activates positive effects and negative ones simultaneously, and the dominant degradation mechanisms evolve with aging time. Degradation mechanisms are discussed. Electric current stress has dual characters: damaging the active layers by generating defects and at the same time improving the p-type conductivity by activating the Mg-dopant. High temperature stresses will promote the effects from electric current stresses. The activation of the Mg-dopant will saturate, whereas the generation of defects is carried on in a progressive way. Other mechanisms, such as deterioration of ohmic contacts, also operate. These mechanisms compete/cooperate with each other and evolve with aging time, resulting in the observed three-stage degradation behavior. There exist risks to predict the lifetime of LEDs by a model with a constant accelerated factor.

Influence of electron distribution on efficiency droop for GaN-based light emitting diodes

“…Compared with LED I, with the indium concentration increasing in the quantum barriers, LED II shows a better electrical performance. However, with the indium further increasing, at the low current region, maybe because of the increased tunneling current due to the indium incorporation, the current density-voltage curve of LED III shifts to smaller current density at the same forward voltage comparing to the LED II [25]. Figure 3 (b) shows the electroluminescence spectra measured at 13.8 A/cm 2 and room temperature for these samples.…”

Optical degradation mechanisms of mid-power white-light LEDs in LM-80-08 tests

“…In Section 3.2, we have found chip-related deterioration at 55°C and 105°C. It has been found that the chip-related degradation of the LED packages is due to either junction deterioration or Ohmic contact deterioration [4,20]. In order to understand the effects of blue chip degradation to optical performance, the I-V characteristics was studied in terms of series resistance and ideality factors at high current region (forward current N 1 mA) by following equation [21]:…”

Degradation and corresponding failure mechanism for GaN-based LEDs

“…Stage I is from 0 h to 300 h, during which the radiant fluxes of these LEDs increase in fluctuation. The increase of the radiant fluxes is related to the increase of the hole concentration in the p-GaN by the activation of the dopant Mg due to the annealing effect, 18 but the fluctuation indicates a competition between the activation of the dopant Mg in the p-GaN and the generation of the defect in the chip. After that, a sudden decay appears indicating a different dominate mechanism during this stage.…”

“…[14][15][16] In addition, during the aging tests, it has been reported that the degradation behaviors and failure mechanisms would be different at different aging states. 17,18 But during the degradation, how the failure mechanism will influence the degradation at the different stages, the origin of the dominant degradation behavior as well as their relationship with the corresponding LED structure have still not been fully understood.…”