Disentangling the Impact of Point Defect Density and Carrier Localization-Enhanced Auger Recombination on Efficiency...

Area of Science:

• Materials Science
• Solid State Physics
• Optoelectronics

Background:

• Internal quantum efficiency (IQE) in (In,Ga)N/GaN quantum wells is high for blue emission but drops for longer wavelengths and higher excitation rates (efficiency droop).
• Efficiency droop limits the brightness of light-emitting diodes (LEDs).
• Proposed mechanisms for droop include Auger recombination, carrier escape, and saturation of localized states, but reconciliation with measurements is challenging.

Purpose of the Study:

• Investigate the dependence of droop behavior on point defect density in (In,Ga)N/GaN quantum wells.
• Develop an atomistic model to understand carrier dynamics and efficiency droop.
• Identify factors limiting peak IQE in green-emitting quantum wells.

Main Methods:

• Experimental photoluminescence measurements across three orders of magnitude of excitation for three differently grown samples.
• Atomistic tight-binding electronic structure modeling to calculate radiative and Auger rates.
• Analysis of carrier density-dependent IQE and decay dynamics.

Main Results:

• Droop behavior was found to be independent of the point defect density in the studied quantum wells.
• The atomistic model accurately reproduced experimental measurements of IQE and carrier decay dynamics.
• Point defects, Auger recombination, and polarization fields limited peak IQE to ~70% in green-emitting quantum wells.

Conclusions:

• Localization-enhanced radiative and Auger rates are crucial for understanding droop.
• External factors like carrier injection efficiency and homogeneity significantly impact the external quantum efficiency of green LEDs.
• The study provides insights into the fundamental mechanisms behind efficiency droop in nitride-based quantum wells.