Degradation mechanism beyond device self-heating in high power light-emitting diodes

Abstract

Temperature-dependence of the internal efficiency droop in GaN-based diodes Appl. Phys. Lett. 99, 181127 (2011) Localized surface plasmon-enhanced electroluminescence from ZnO-based heterojunction light-emitting diodes Appl. Phys. Lett. 99, 181116 (2011) Performance enhancement of blue light-emitting diodes with AlGaN barriers and a special designed electronblocking layer J. Appl. Phys. 110, 093104 (2011) A light emitting diode based photoelectrochemical screener for distributed combinatorial materials discovery Rev. Sci. Instrum. 82, 114101 (2011) Promotion of hole injection enabled by GaInN/GaN light-emitting triodes and its effect on the efficiency droop Appl. Phys. Lett. 99, 181115 (2011) Additional information on J. Appl. Phys. A unique degradation property of high power InGaN/GaN multiple quantum well (MQW) white light-emitting diodes (LEDs) was identified. The LEDs were stressed under different forwardcurrents. The various ageing characteristics were analyzed for both the electrical response and electro-luminescence (EL) spectra. The Raman spectroscopy allowed noninvasive probing of LED junction temperature profiles which correlated well with the EL characteristics, showing a junction temperature drop during degradation at certain current levels. In addition to the common observations: (1) a broadening of the light intensity-current (L-I) characteristic in the nonlinear regime, and (2) a shift of the current-voltage (I-V) dependence to higher current levels, the EL spectra showed different temperature responses of the two blue emission peaks, 440 and 463 nm. The former was temperature sensitive and thus related to shallow defect levels, while the latter was thermally stable and deeper defect states were involved in the degradation process. This unique selection rule resulted in the enhancement of the blue emission peak at 463 nm after degrading the LEDs. This study suggests that LED device heating is not directly linked to the degradation process.

Defects dynamics during ageing cycles of InGaN blue light-emitting diodes revealed by evolution of external quantum efficiency - current dependence

“…Ageing improves the low current EQE, but at high current it leads to lower EQEs as well as higher droop rates. Figure 1(f) shows that the maximum EQE vs. ageing time for 3 devices, exhibiting non-monotonic behavior with peaks at τ a = ~500 h. Our ageing data for high current contradict to most of the previous reports where monotonic darkening at high current was observed with ageing [18][19][20][21][22]. There are nonetheless some literature reported the similar initial intensity increase [15][16][17].…”

Failure mechanisms in blue InGaN/GaN LEDs for high power operation

“…However the most important physical mechanisms that responsible for unreliability of GaN-based LEDs in solid-state lighting origin not clarified until now, despite nearly 20 years of efforts made by research groups in the industrial countries [1,2]. It is clear now that degradation of power InGaN/GaN LEDs is a multi-faceted problem that involves change of defect population, catastrophic optical destruction, metal diffusion and electrode delamination [3,4]. The increase in the nonradiative recombination in the active junction of the LEDs due to the propagation of defects and the migration of the indium and impurities in the multiple quantum well (MQW) region is observed [4].…”

“…It is important to note the difficulties in identifying a specific degradation mechanism in different types of LEDs. In fact, different causes may dominate even in a single type of diode, and different degradation mechanisms can be observed simultaneously [4]. One can believe that the difficulties are related with numerous forms of nanostructural arrangement (NA) in the GaN-based LEDs.…”

“…It is clear now that degradation of power InGaN/GaN LEDs is a multi-faceted problem that involves change of defect population, catastrophic optical destruction, metal diffusion and electrode delamination [3,4]. The increase in the nonradiative recombination in the active junction of the LEDs due to the propagation of defects and the migration of the indium and impurities in the multiple quantum well (MQW) region is observed [4]. It is important to note the difficulties in identifying a specific degradation mechanism in different types of LEDs.…”

Investigation of efficiency droop for UV LED with N-type AlGaN layer

“…On the other hand, the junction temperature, the temperature of the active region, is a critical parameter and affects quantum efficiency of device, maximum output power, reliability, and other parameters. In general, heat can be generated in the ohmic contact, cladding layers, and the non-radiative recombination in the active region [7]. In this study, we proposed to remove the conventional n-type GaN below InGaN multi-quantumwells (MQWs) and replaced it with an n-type Al 0.03 Ga 0.97 N to improve the optical performance in the UV GaN LEDs.…”