Indium gallium nitride-based ultraviolet, blue, and green light-emitting diodes functionalized with shallow periodic hole patterns

Hyun Jeong,Gilles Lerondel,Rafael Salas-Montiel,Mun Seok Jeong

doi:10.1038/srep45726

Abstract

In this study, we investigated the improvement in the light output power of indium gallium nitride (InGaN)-based ultraviolet (UV), blue, and green light-emitting diodes (LEDs) by fabricating shallow periodic hole patterns (PHPs) on the LED surface through laser interference lithography and inductively coupled plasma etching. Noticeably, different enhancements were observed in the light output powers of the UV, blue, and green LEDs with negligible changes in the electrical properties in the light output power versus current and current versus voltage curves. In addition, confocal scanning electroluminescence microscopy is employed to verify the correlation between the enhancement in the light output power of the LEDs with PHPs and carrier localization of InGaN/GaN multiple quantum wells. Light propagation through the PHPs on the UV, blue, and green LEDs is simulated using a three-dimensional finite-difference time-domain method to confirm the experimental results. Finally, we suggest optimal conditions of PHPs for improving the light output power of InGaN LEDs based on the experimental and theoretical results.

Highlights

We can conclude that the increases of external quantum efficiencies (EQEs) are induced by enhanced light extraction efficiency (LEE) From the L–I–V measurements, we determined that the enhancement in the light output power of the light-emitting diodes (LEDs) with periodic hole patterns (PHPs) is sensitive to the emission wavelength and a small depth of holes significantly affects the light output power of the LEDs, with only limited slight changes in the electrical properties
The PHPs were fabricated through laser interference lithography and inductively coupled plasma (ICP) etching on the top surface of the LEDs
The L–I and I–V curves show the different enhancements in the light output powers of the UV, blue, and green LEDs with PHPs, with slight changes in the electrical properties

Summary

Results

Region, which is the border between the ITO and p-GaN electrical safety margin area. The inset shows the magnified SEM image of the p-GaN surface. Different absolute values of the light output power as a function of the emission wavelength are a typical feature of InGaN-based LEDs.[37,38] Figure 3(d) and (f) respectively show the I–V curves of the blue and green LEDs, in which the hollowed red and black squares indicate the data points for the LEDs with and without PHPs, respectively. The theoretical results of the LEE enhancement factors according to the emission wavelength and hole pattern depths confirm the experimental data and present an efficient method to improve the light output power of InGaN LEDs using PHPs. While having a perforated thin film on the top of device, one could evoke a better light extraction through a refractive index matching layer. We observed enhanced EL intensities detected from the p- and n-GaN layers of the UV, blue, and green LEDs owing to the formation of PHPs, indicating that the final enhancement in the light output power is partially contributed by this enhancement. (see Supplementary Information, Fig. S5)

Discussion

Findings

Methods