III-nitride LEDs with photonic crystal structures

Performance and trends of high power light emitting diodes

“…Extraction efficiencies for unencapsulated LEDs can be increased as well using photonic crystal (PC) structures as e.g. described by J. Wierer et al [5] Angular beam shaping using photonic crystals (see Figure 7) can further increase the effective luminance, useful for projection, by controlling the angular emission pattern. But close attention should be paid to the trade-offs between the overall extraction efficiency versus the flux within the target cone.…”

“…4 Better optical coupling efficiency with Flip Chip designs. 5 Better reliability at high currents and junction temperatures.…”

Further enhancement of light extraction efficiency from light emitting diode using triangular surface grating and thin interface layer

“…A number of research papers have been published, suggesting ways to improve the LEE or the external quantum efficiency in LEDs. Random surface texturing or roughening [3][4][5], periodic surface modification in the form of nanopyramids [6] or surface gratings [7], and exploiting photonic crystals (PCs) [8][9][10][11][12][13] or surface plasmon resonance [14,15] are some of the interesting approaches aimed at increasing the LEE of LEDs. Interesting reports [16] are also made on improving the efficiency by using top transmission gratings only.…”

Comparison of numerical modeling and experiments of InGaN quantum wells light-emitting diodes with SiO 2 /polystyrene microlens arrays

“…The total internal reflection leads to narrow escape cone of only ~23.5 0 with escape probability of only ~ 4 % from top surface of the LEDs device, due to the optical modes being trapped inside the semiconductor. Several approaches have been implemented to improve the light extraction efficiency of the InGaN QW LEDs, such as: die-shaping approach [7,8], surface roughening approach [9][10][11], oblique mesa sidewall approach [12], photonic crystals approach [13][14][15][16], nano-pyramid approach [17], sapphire microlenses approach [18] and grading refractive indices between semiconductor/air interface with planar material approach [19][20][21]. The use of die-shaped LEDs devices results in promising device performance, but the high cost associated with die shaping technique remains an important limitation.…”