Metasurface-Based Phosphor-Converted Micro-LED Architecture for DisplaysCreating Guided Modes for Enhanced Directionality

Phosphor-converted micro-light emitting diodes (micro-LEDs)
are
a crucial technology for display applications but face significant
challenges in light extraction because of the high refractive index
of the blue pump die chip. In this study, we design and experimentally
demonstrate a nanophotonic approach that overcomes this issue, achieving
up to a 3-fold increase in light extraction efficiency. Our approach
involves engineering the local density of optical states (LDOS) to
generate quasi-guided modes within the phosphor layer by strategically
inserting a thin low-index spacer in combination with a metasurface
for mode extraction. We demonstrate the trade-offs between blue light
pumping, LDOS enhancement at the converted emission wavelength, and
radiation pattern control using a stratified system solver for dipole
emission. Experimentally, the integration of plasmonic antennas and
a silica spacer resulted in a 3-fold overall brightness enhancement,
with nearly a 4-fold increase in forward emission. This nanophotonic
metasurface waveguide design is a critical advancement for producing
bright, directional micro-LEDs, particularly in augmented/virtual
reality (AR/VR) devices and smartwatch displays, without the need
for bulky secondary optics or reflectors.