Disentangling the Impact of Point Defect Density and Carrier Localization-Enhanced Auger Recombination on Efficiency Droop in (In,Ga)N/GaN Quantum Wells

Abstract

The internal quantum efficiency of (In,Ga)N/GaN quantum wells can surpass 90% for blue-emitting structures at moderate drive current densities but decreases significantly for longer emission wavelengths and at higher excitation rates. This latter effect is known as efficiency "droop" and limits the brightness of light-emitting diodes (LEDs) based on such quantum wells. Several mechanisms have been proposed to explain efficiency droop including Auger recombination, both intrinsic and defectassisted, carrier escape, and the saturation of localized states. However, it remains unclear which of these mechanisms is most important because it has proven difficult to reconcile theoretical calculations of droop with measurements. Here, we first present experimental photoluminescence measurements extending over three orders of magnitude of excitation for three samples grown at different temperatures that indicate that droop behavior is not dependent on the point defect density in the quantum wells studied. Second, we use an atomistic tight-binding electronic structure model to calculate localization-enhanced radiative and Auger rates and show that both the corresponding carrier density-dependent internal quantum efficiency and the carrier density decay dynamics are in excellent agreement with our experimental measurements. Moreover, we show that point defect density, Auger recombination, and the effect of the polarization field on recombination rates only limit the peak internal quantum efficiency to about 70% in the resonantly excited green-emitting quantum wells studied. This suggests that factors external to the quantum wells, such as carrier injection efficiency and homogeneity, contribute appreciably to the significantly lower peak external quantum efficiency of green LEDs.

Carrier density dependent Auger recombination in c-plane (In,Ga)N/GaN quantum wells: insights from atomistic calculations

“…Also our calculations show that with increasing carrier density the electron-electron-hole (eeh) Auger rate is of secondary importance when compared to the hole-holeelectron rate (hhe). Finally, on average we find a total Auger coefficient >10 −31 cm 6 s −1 , which is usually regarded as large enough to facilitate the efficiency 'droop' in (In,Ga)N based LEDs [2,19] and is further supported by our recent theory experiment comparison [20].…”

“…about the simulation cell, can be found in [15]. Overall, the assumed composition and well width are often found in experimental realisations of (In,Ga)N/GaN QWs [17,18,20].…”

“…much faster non-radiative recombination processes) in different areas of a sample. While these 'outlier' configurations may not be representative of the experiments in [20], where it is concluded that defect-assisted Auger processes are of secondary importance in the samples studied, from a theoretical perspective it is nevertheless interesting to study the carrier density dependence of the Auger recombination in such an 'extreme' configuration. Overall, the three selected configurations furnish a good overview of how Auger coefficients may change with carrier density in (In,Ga)N/GaN QW systems.…”

“…To investigate the carrier density dependence of the Auger rate and thus the Auger coefficients, we have chosen three configurations from the previously studied ten, guided by the following considerations. The experimental data in [20] on (In,Ga)N/GaN QWs with well widths and In contents similar to the systems considered here indicated that for high carrier densities in the wells, the measured optical properties did not vary significantly between different spots on the sample; all the measurements in [20] were carried out at a temperature of 300 K. To take these findings into account, we aimed for two configurations that reflect the 'most commonly' found Auger coefficients in our theoretical analysis. Based on this we selected Cfs.…”

Tuning Ultrafast Carrier Dynamics and Broadband Photo-Response of High-Performance Sb2Se3 Thin Film Photodetectors: A Substrate Dependent Study

“…This carrier lifetime dependency can be because of either radiative recombination or Auger recombination due to trap states . At high pump powers, certain carrier recombination mechanisms may approach saturation, leading to more rapid and efficient recombination pathways, thereby decreasing carrier lifetime. , Notably, since Sb 2 Se 3 is an indirect band gap material and does not exhibit photoluminescence (PL), radiative recombination is not feasible.…”