High Luminous Efficacy Phosphor-Converted Mass-Produced White LEDs Achieved by AlN Prebuffer and...

Area of Science:

• Materials Science
• Solid State Physics
• Optoelectronics

Background:

• Improving luminous efficacy (ηL) of nitride-based light-emitting diodes (LEDs) is crucial for energy savings and cost reduction.
• Approaching the efficiency limit of this material system requires innovative strategies.

Purpose of the Study:

• To enhance the efficiency of white LEDs (WLEDs) by employing a thin aluminum nitride (AlN) prebuffer and a transitional-refraction-index patterned sapphire substrate (TPSS).
• To investigate the impact of these strategies on light output power (φe) and external quantum efficiency (ηext) of blue LEDs (BLEDs).

Main Methods:

• Fabrication of AlN prebuffer using physical vapor deposition (PVD).
• Fabrication of TPSS via dry-etched periodic silica arrays on sapphire.
• Performance evaluation using Monte Carlo ray-tracing simulations and experimental measurements on mass-produced devices.

Main Results:

• PVD AlN prebuffer improved BLED light output power (φe) by 2.53% and increased productivity by ~8%.
• BLEDs on TPSS showed a 5.65% enhancement in external quantum efficiency (ηext) compared to conventional patterned sapphire substrates (PSS).
• Experimental enhancement of BLED φe by 10% at 40 A/cm² was achieved.
• Phosphor-converted WLEDs reached a peak luminous efficacy (ηL) of 295.2 lm/W at 0.9 A/cm² and 282.4 lm/W at 5.6 A/cm².

Conclusions:

• The combined use of PVD AlN prebuffer and TPSS significantly boosts the efficiency and productivity of nitride-based LEDs.
• These advancements contribute to achieving higher luminous efficacy in WLEDs, approaching theoretical limits.
• The developed methods offer a viable path for cost-effective, high-efficiency LED manufacturing.