Enhancement in external quantum efficiency of AlGaInP red μ-LED using chemical solution treatment process

Abstract

To investigate the effects of their surface recovery and optical properties, extremely small sized (12 µm × 12 µm mesa area) red AlGaInP micro light emitting diodes ($$\upmu$$ μ LED) were fabricated using a diluted hydrofluoric acid (HF) surface etch treatment. After the chemical treatment, the external quantum efficiencies (EQEs) of $$\upmu$$ μ -LED at low and high injection current regions have been improved by 35.48% and 12.86%, respectively. The different phenomena of EQEs have a complex relationship between the suppression of non-radiative recombination originating from the etching damage of the surface and the improvement of light extraction of the sidewalls. The constant enhancement of EQE at a high injection current it is attributed to the expansion of the active region’s sidewall surface area by the selective etching of AlInP layers. The improved EQE at a low injection current is related to the minimization of the surface recombination caused by plasma damage from the surface. High-resolution transmission electron microscopy (HR-TEM) revealed physical defects on the sidewall surface, such as plasma-induced lattice disorder and impurity contamination damage, were eliminated using chemical treatment. This study suggests that chemical surface treatment using diluted HF acid can be an effective method for enhancing the $$\upmu$$ μ -LED performance.

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro‐LEDs

“…Similar result of suppressing YL band by sol-gel SiO2 was reported elsewhere [16]. The most important thing in the performance of µLEDs is the sidewall condition [34][35][36][37][38][39][40]. Except for special cases, such as semipolar and nonpolar GaN LEDs, most GaN-based LED wafers are grown on c-plane sapphire, and hence the sidewall should have a non-polar surface such as m-plane orientation (Figure 2).…”

Recent Advances in Micro-LEDs Having Yellow–Green to Red Emission Wavelengths for Visible Light Communications

“…Although AlGaInP-based red micro-LEDs demonstrated higher VLC performance, they had serious surface recombination problems that cause instability at high temperatures and size-dependent efficiency droop [ 66 , 67 , 68 , 69 , 70 , 71 , 72 ]. As a result, it is desirable to develop monolithic RGB micro-LED technology using InGaN-based red micro-LEDs.…”

Developments for enhancing the luminous intensity of LEDs by optimizing their structures

“…Firstly, the n-GaN needs to be exposed to enable the deposition of electrode on it. To expose the n-GaN, some fractions of p-GaN and MQW needs to be etched by inductively coupled plasma (ICP) [19] or using the wet etch method [20]. Therefore, the loss of MQW region will decrease the volume available for the electrons and holes to recombine.…”