Abstract
We propose an unconventional out-coupling structure consisting of two-dimensional periodic metal-dielectric patterns. Numerical simulations show that low orders of guided modes are extracted efficiently by the metal-dielectric pattern with a pitch size of ~(λ/n) and pattern depth of <100 nm. Vertical GaN light-emitting diodes with optimized metal-ITO patterns exhibited extraction efficiencies enhanced by factors of 6.6 and 2.6 for perfect conductor and silver metals, respectively, as compared to a non-patterned structure. The plasmonic absorption loss from the corrugated silver mirror accounts for the relatively smaller enhancement in extraction efficiency with the silver-ITO pattern. Furthermore, a double-sided out-coupling structure consisting of an upper GaN-air pattern and a bottom perfect conductor-ITO pattern exhibited a 40% enhancement in extraction efficiency as compared to the structure with single GaN-air pattern. We believe that deep understandings of the interaction between light and metal-dielectric patterns will lead to improved device performances in various optoelectronic applications including high-efficiency light-emitting diodes.
Highlights
Semiconductor light-emitting diodes (LEDs) show unique advantages such as easy integration with other optical components, high color rendering index, and long device life time
Laser or chemical lift-off GaN vertical LEDs have become crucial for high-output applications such as general illumination and backlight units for largearea displays because of its efficient thermal dissipation and uniform current flow [6,8,13,14,15]
In simulations, square-lattice periodic patterns consisting of ITO and perfect conductor (PC) were used for the bottom out-coupling structure
Summary
Semiconductor light-emitting diodes (LEDs) show unique advantages such as easy integration with other optical components, high color rendering index, and long device life time. Regarding the improvement of out-coupling efficiency, several ideas have been proposed such as surface roughening [2,3,4], periodic patterning [5,6,7,8], and resonant cavity effects [9,10,11]. Laser or chemical lift-off GaN vertical LEDs have become crucial for high-output applications such as general illumination and backlight units for largearea displays because of its efficient thermal dissipation and uniform current flow [6,8,13,14,15]. We propose a GaN vertical LED with a two-dimensional (2D) periodic metal-dielectric pattern as an efficient out-coupling structure. We illustrate extraction mechanisms and design rules of the metal-dielectric patterns that distinguish them from conventional dielectric out-coupling patterns
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