Highly efficient and reliable high power InGaN/GaN LEDs with 3D patterned step‐like ITO and wavy sidewalls

Abstract

Nitride‐based high power LEDs with finger‐like SiO2 current blocking layer (CBL), three‐dimensional (3D) patterned step‐like ITO double layers and wavy sidewalls were fabricated. The finger‐like SiO2 CBL beneath finger‐like p‐electrode was designed to prevent current crowding effect, thereby facilitating uniform current spreading over the entire chip. In addition, 3D patterned step‐like ITO double layers, including alternating 230 nm thick patterned upper step ITO layer and 100 nm thick lower step ITO layer, were formed by combining photolithography and aqua regia etchant. We showed that the top light extraction efficiency of high power LEDs can be significantly enhanced by taking 3D patterned step‐like ITO. The light output power of high power LEDs with 3D patterned step‐like ITO double layers is 13.9% higher than that of LEDs with smooth ITO layer. High‐power LEDs with wavy sidewalls was fabricated by an optimized mask design in conjunction with dry etching process based on Cl2/BCl3 to improve light extraction efficiency at the horizontal direction. We demonstrated that light output power of high power LEDs with wavy sidewalls can be improved by 11% as compared to LEDs with flat sidewalls.

Light-emitting diodes with surface gallium nitride p–n homojunction structure formed by selective area regrowth

“…The external quantum efficiency (EQE) of an LED depends on the internal quantum efficiency (IQE) and light extraction efficiency (LEE) of photons emitted from the active layer of the LED. Most studies aimed at enhancing the LEE focused on reducing photon loss due to total internal reflection inside LEDs 2–5 . At present, efficiency droop, which is the nonthermal rollover of IQE at a high-current density in III-nitride LEDs remains a critical issue.…”

Light Extraction Enhancement of InGaN Based Micro Light-Emitting Diodes with Concave-Convex Circular Composite Structure Sidewall

“…In particular, the LOP of Device C using the concave-convex circular composite structure sidewalls with a radius of 2 µm is increased by 7.2%. This is because the patterned sidewalls structure reduces the TIR of the micro-LEDs, increasing the emitting probability of photons at the sidewalls and thereby increasing the LEE by permitting photons to find the escape cones of the horizontal direction [32,33,36]. However, the LOP of Device B using concave circular sidewalls is only increased by 1%, which is lower than those of Devices C-F using concave-convex circular composite structure sidewalls.…”

“…Meanwhile, the LEE can be improved by roughening the bottom [30] or sidewalls of the LED. Wherein, the methods of roughening the sidewalls mainly include convex structure [9,31,32], and wave structure [33]. Due to the difference in the size of the active region between the micro-LED and the large-sized LED, the general patterned sidewall cannot effectively improve the light efficiency for micro-LED due to the reduction of the limited active region area.…”

Two-step passivation for enhanced InGaN/GaN light emitting diodes with step graded electron injectors

“…The plasma damage manifests itself as generation of point defects, primarily nitrogen vacancies, which act as donors [27,28]. There are other ways to improve light output such as using encapsulants with high refractive indices [29,30], patterning of current spreading layer surface [21,31], using patterned sapphire substrates [13], patterning of passivation layer surface [13,14], and employing antireflection optical coatings and two-dimensional photonic crystals [12,32]. One of the practical ways for light extraction improvement of front emitting LED chip that does not degrade its electrical properties is patterning of the passivation layer [13,14].…”