Temperature-dependent efficiency droop of blue InGaN micro-light emitting diodes

Abstract

Temperature-dependent trends in radiative and Auger recombination coefficients have been determined at different injection carrier concentrations using InGaN micro-light emitting diodes 40 μm in diameter. The differential lifetime was obtained first from the measured modulation bandwidth and was then employed to calculate the carrier concentration in the quantum well active region. When the temperature increases, the carrier concentration increases, but both the radiative and Auger recombination coefficients decrease. In addition, the temperature dependence of radiative and Auger recombination coefficients is weaker at a higher injection carrier concentration, which is strongly related to phase space filling

Aging characteristics of blue InGaN micro-light emitting diodes at an extremely high current density of 3.5 kA cm−2

“…The schematic structure of the micro-LEDs is shown in figure 1(a). The fabricated micro-LEDs have a emission wavelength ∼445 nm and the micro-LED efficiency is similar to that in [14]. Micro-LED sizes of 20 µm, 40 µm and 60 µm in diameter were chosen for aging test at a current density 3.5 kA/cm 2 under room temperature ∼25 • C. These micro-LEDs were mounted on a PCB with a fixed distance to a Si detector for measurement of light output power and the ambient temperature was monitored by a thermometer.…”

Effect of Die Shape and Size on Performance of III-Nitride Micro-LEDs: A Modeling Study

“…Only recently, the efficiency improvement had become a hot topic in the research and development of µ-LEDs. Typically, maximum values of external quantum efficiency (EQE) of µ-LEDs did not exceed 10% [7,8], which could be attributed to non-optimal light extraction from the LED dice. A record EQE of 42% at the current density of 50 A/cm 2 was recently demonstrated for 10 × 10 µm 2 devices and light extraction to silicone with the refractive index of 1.41 [3].…”

“…As the recombination processes in InGaN quantum wells (QWs), serving as active regions in III-nitride LEDs, are interfered with by carrier localization due to composition fluctuations in InGaN alloys [11,12] and a strong electric field induced in polar InGaN QWs [13], no consensus has currently been reached regarding temperature dependence of the recombination coefficients. Experimentally, there is a limited number of reports [7,14,15] providing highly scattered and contradictory information on the dependence of recombination coefficients on temperature. Hence, this problem should be resolved in order to get predictive simulations of μ-LEDs.…”

Diffusion-Driven Charge Transport in Light Emitting Devices

“…In the droop-effect, an increasing injection current leads to significant drop off in the emission efficiency of blue LEDs with indium gallium nitride (InGaN) MQW active layers [ 18 , 19 , 20 ]. The mechanisms of the efficiency droop in InGaN LEDs have been studied extensively, where carrier delocalization [ 21 , 22 , 23 ] and electron leakage [ 18 , 24 ] are proposed to be key reasons, while the most recent reports mainly pointing to Auger recombination as the main culprit [ 25 , 26 , 27 , 28 ]. Secondly, particularly in the modern high quantum efficiency LEDs, the efficiency droop limitations, current crowding and resistive loss become the most severe bottlenecks for high output power devices, confining their optimal high-efficiency performance at current densities well below 100 A/cm [ 29 , 30 , 31 , 32 , 33 , 34 ].…”