A red-emitting micrometer scale LED with external quantum efficiency >8%

Abstract

Significant efforts are being put into the development of efficient micrometer-scale light emitting diodes (LEDs) for future display technologies due to their marked benefits over existing displays. To date, however, the efficiency of microLED devices remains significantly lower than that of conventional broad-area devices. The deterioration in device performance with smaller device size has been linked to the plasma damage induced on mesa sidewalls during device fabrication. Here, we studied bottom-up red-emitting nanowire LEDs with different Mg doping levels in the p-GaN layer. The resulting sub-micron LED devices show a distinct improvement in efficiency with increasing Mg dopant incorporation. Through optimization of the doping, we measured an external quantum efficiency of ∼8.3% and a wall-plug efficiency of ∼4.6%, at a current density of ∼1 A/cm2, for a red-emitting sub-micrometer scale LED operating at >630 nm. This study highlights the importance of p-doping in microLEDs for attaining high efficiency performance in nanostructure-based devices.

Recent Progress in Long‐Wavelength InGaN Light‐Emitting Diodes from the Perspective of Epitaxial Structure

“…[113] Through optimization of the Mg doping within the nanowires, the plasma damage-induced deleterious effect can be eliminated, resulting in a peak EQE and WPE of %8.3% and %4.6% for submicrometer red LEDs with an emission wavelength at %650 nm. [114] Remarkably, as the diameter of nanowires decreases, the lateral diffusion of In adatoms is significantly enhanced, resulting in an increase of In incorporation and longer emitting wavelengths. [115] This observation is crucial for the development of monolithically integrated full-color micro-LEDs, offering a new avenue toward the creation of ultrasmall and ultrahigh resolution displays, as shown in Figure 7b-d.…”

In‐Plane Sensing Opportunities in MicroLED Displays

“…Such miniaturization is economically essential to enable appreciable volumes 34 . The miniaturization is particularly challenging for red because of the technological challenges posed by the III‐V semiconductors used for direct red emitters 35 . Other factors include reliability, efficiency, absorption, and environmental challenges of down‐conversion materials 36 when applied to high spatial resolutions, such as those matching human visual acuity at normal direct‐viewing distance (e.g., in a smartwatch or smartphone).…”

Impact of Charge Carrier Transfer and Strain Relaxation on Red-Emitting InGaN/GaN Heterostructures

“…Moreover, the core−shell structure has been widely observed in nanowire InGaN/GaN heterostructures due to the unique migration-assisted growth mechanism, which suppresses nonradiative surface recombination. 9,14,15 In this work, we report a charge carrier transfer process in InGaN/GaN nanowire heterostructures, wherein InGaN with different indium compositions is spontaneously formed on the c-plane and semipolar plane, respectively. As schematically shown in Figure 1b, photoinduced charge carriers in c-plane InGaN relocalize to the semipolar-plane InGaN through a nonradiative transfer process and then radiatively recombine, which leads to efficient emissions over a wide excitation power range.…”

“…III-nitride visible light emitters with micro- or submicrometer sizes are essential building blocks for next-generation displays and the emerging applications including augmented and virtual reality (AR/VR) systems. − Recently, significant progress has been made in high-efficiency blue and green microlight-emitting diodes (μLEDs) as well as multicolor integration, − while extensive efforts have been devoted in high-performance red-emitting μLEDs with high indium composition InGaN as the active regions. − However, the incorporation of high indium composition causes alloy substitutional disorder in the active region and reduces the exciton binding energy, which enhances the Auger recombination coefficient. Polar nitrides also suffer from quantum-confined Stark effect (QCSE) due to spontaneous and piezoelectric polarizations, which reduces the overlap of electron–hole wave functions and causes color instability as is depicted in Figure a.…”

“…Meanwhile, the nanowire structure offers additional strain relaxation due to a high surface-to-volume ratio. Moreover, the core–shell structure has been widely observed in nanowire InGaN/GaN heterostructures due to the unique migration-assisted growth mechanism, which suppresses nonradiative surface recombination. ,, …”