Efficiency improvement of a vertical light-emitting diode through surface plasmon coupling and grating scattering

Area of Science:

• Optoelectronics
• Materials Science
• Nanotechnology

Background:

• Vertical light-emitting diodes (LEDs) often suffer from efficiency droop and limited output intensity.
• Surface plasmon (SP) coupling offers a potential route to enhance light extraction efficiency in LEDs.

Purpose of the Study:

• To demonstrate enhanced output intensity, polarized output, and reduced efficiency droop in SP-coupled vertical LEDs.
• To investigate the role of nano-grating structures in SP coupling with InGaN/GaN quantum wells (QWs).

Main Methods:

• Fabrication of vertical LEDs using a photoelectrochemical liftoff technique to remove the patterned sapphire substrate.
• Integration of an Ag nano-grating structure between the p-GaN layer and wafer bonding metal for SP coupling.
• Addition of a surface grating structure on the n-GaN side for further enhancement.

Main Results:

• The Ag nano-grating structure effectively induces SP coupling with InGaN/GaN QWs, primarily through localized surface plasmon (LSP) resonance.
• Output intensity and output polarization ratio are significantly enhanced by the nano-grating structures.
• The efficiency droop effect in the vertical LEDs is substantially suppressed.

Conclusions:

• Ag nano-gratings are effective for enhancing light extraction and polarization in vertical LEDs via SP coupling.
• LSP resonance at the metal grating crest is the dominant mechanism for SP-QW coupling.
• Further optimization with additional surface gratings can further improve LED performance and reduce efficiency droop.