Mitigating Structural Defects in Droop-Minimizing InGaN/GaN Quantum Well Heterostructures
- Lumileds
Modern commercial InGaN/GaN blue LEDs continue to suffer from efficiency droop, a reduction in efficiency with increasing drive current. External quantum efficiency (EQE) typically peaks at low drive currents (< 10 A cm2) and drops monotonically at higher current densities, falling to <85% of the peak EQE at a drive current of 100 A cm2. Mitigating droop-related losses will yield tremendous gains in both luminous efficacy (lumens/W) and cost (lumens/$). Such improvements are critical for continued large-scale market penetration of LED technologies, particularly in high-power and high flux per unit area applications. However, device structures that reduce droop typically require higher indium content and are accompanied by a corresponding degradation in material quality which negates the droop improvement via enhanced Shockley-Read-Hall (SRH) recombination. In this work, we use advanced characterization techniques to identify and classify structural defects in InGaN/GaN quantum well (QW) heterostructures that share features with low-droop designs. Using aberration-corrected scanning transmission electron microscopy (Cs-STEM), we find the presence of severe well width fluctuations (WWFs) in a number of low droop device architectures. However, the presence of WWFs does not correlate strongly with external quantum efficiency nor defect densities measured via deep level optical spectroscopy (DLOS). Hence, performance losses in the heterostructures of interest are likely dominated by nanoscale point or interfacial defects rather than large-scale extended defects.
- Research Organization:
- Lumileds LLC, San Jose, CA; Massachusetts Institute of Technology, Cambridge, MA; Brookhaven National Laboratory, Upton, NY; Sandia National Laboratories, Albuquerque, NM
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Building Technologies Office (EE-5B)
- DOE Contract Number:
- EE0007136
- OSTI ID:
- 1364446
- Report Number(s):
- DOE-LL--0007136-1
- Country of Publication:
- United States
- Language:
- English
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