Comparative study on luminescence extraction strategies of LED by large-scale fabrication of nanopillar and nanohole structures

Abstract

Light extraction and current injection are two important considerations in the development of high efficiency light-emitting-diodes (LEDs), but usually cannot be satisfied simultaneously in nanostructure patterned devices. In this work, we investigated near-UV LEDs with nanopillar and nanohole patterns to improve light extraction efficiency. Photoluminescence (PL) intensities were enhanced by 8.0 and 4.1 times for nanopillar and nanohole LEDs compared to that of planar LED. Nanopillar LED exhibits higher PL emission than that of the nanohole LED, attributing to a convex shape sidewall for more effective outward light scattering, and reduction of quantum-confined-stark-effect owing to strain relaxation. However, nanopillar LED exhibits lower electroluminescence intensity than the nanohole sample, which calls for further optimization in carrier distributions. Experimental results were further supported by near-field electric field simulations. This work demonstrates the difference in optical and electrical behaviors between the nanopillar and nanohole LEDs, paving the way for detailed understanding on luminescence extraction mechanisms of nanostructure patterned UV emitters.

On the Luminescence Properties and Surface Passivation Mechanism of III- and N-Polar Nanopillar Ultraviolet Multiple-Quantum-Well Light Emitting Diodes

“…The highest PL enhancement reached 2.4 times for RTA of 900 °C. This can be well explained by the passivation of surface traps and the healing of surface-related defects [14]. However, the luminescence spectra were dramatically different for N-polar nanopillar MQWs.…”

“…No obvious variation in peak position is observed between planar and nanostructured sample. However, an enhanced luminescence intensity is identified for the nanostructured sample due to enhanced light scattering effect [14].…”

“…Currently, most of the nanostructured UV-LEDs are fabricated by reactive ion etching (RIE) due to better control over morphologies and sizes of the nanostructures [14]. However, RIE introduces surface defect states that will lead to reduced external quantum efficiency (EQE) and degraded output power of LEDs through Shockley-Read-Hall (SRH) non-radiative recombination [15].…”

Omnidirectional whispering-gallery-mode lasing in GaN microdisk obtained by selective area growth on sapphire substrate

“…In addition, since reactive ion etching (RIE) is usually applied in the formation of the III-nitride WGM microdisk, severe light scattering and large optical losses are inevitable as mask erosion during RIE results in rough sidewalls and degradation of circularity of the GaN microdisks [7]. Compared to GaN microdisk fabricated by RIE [8], microdisks obtained by bottom-up growth method have advantages, such as higher crystalline quality, naturally formed crystallographic planes acting as side-reflecting mirrors, and consequently improved lasing characteristic [9].…”

Mechanism of Improved Luminescence Intensity of Ultraviolet Light Emitting Diodes (UV-LEDs) Under Thermal and Chemical Treatments

“…In optoelectronic devices, similar passivation techniques can be found in literatures, especially in LDs operating under high current level [11], [12]. Thermal annealing was also performed after device fabrication, mainly post-metallization annealing for Ohmic contact optimization [13], [14], or p-GaN activation [15].…”