Abstract
Current solutions for improving the light extraction efficiency of flip-chip light-emitting diodes (LEDs) mainly focus on relieving the total internal reflection at sapphire/air interface, but such methods hardly affect the epilayer mode photons. We demonstrated that the prism-structured sidewall based on tetramethylammonium hydroxide (TMAH) etching is a cost-effective solution for promoting light extraction efficiency of flip-chip mini-LEDs. The anisotropic TMAH etching created hierarchical prism structure on sidewall of mini-LEDs for coupling out photons into air without deteriorating the electrical property. Prism-structured sidewall effectively improved light output power of mini-LEDs by 10.3%, owing to the scattering out of waveguided light trapped in the gallium nitride (GaN) epilayer.
Highlights
The developments in gallium nitride (GaN)-based light-emitting diodes (LEDs) have promoted the liquid crystal display (LCD) as a highly competitive display technology in the past few decades [1,2]
We demonstrated that the prism-structured sidewall based on tetramethylammonium hydroxide (TMAH) etching is a cost-effective solution for promoting light extraction efficiency of flip-chip mini-LEDs
To meet the high dynamic range (HDR) requirements of generation displays, the luminance of the LCD bright state should be over 1000 nits, which requests the mini-LED backlight unit to be much more energy efficient [5]
Summary
The developments in GaN-based light-emitting diodes (LEDs) have promoted the liquid crystal display (LCD) as a highly competitive display technology in the past few decades [1,2]. The application of mini-LEDs with size below 200 microns gains new advantages for LCDs in market competition owing to their prominent merits as backlight unit, such as long life span, low energy consumption and high resolution [3,4]. Tremendous efforts have been done to improve the efficiency of GaN-based LEDs, which can be principally divided into two categories: improving the crystal quality of epilayer [6,7,8,9,10] and boosting the light extraction efficiency (LEE) [11,12,13,14,15]. Since the ratio of top emitting area to sidewall emitting area is greatly different for mini-LEDs and broad-area LEDs, the methods applicable in broad-area LEDs for improved LEE need to be reassessed in mini-LEDs
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