# A Colloidal-Quantum-Dot Integrated U-Shape Micro-Light-Emitting-Diode and Its Photonic Characteristics

## TL;DR

A U-shaped micro LED integrated with colloidal quantum dots converts blue light to green or red and shows improved efficiency and longevity.

## Contribution

A novel U-shaped micro LED design with integrated colloidal quantum dots for enhanced color conversion and extended CQD lifetime.

## Key findings

- The U-shape micro LED with CQDs achieves a color conversion efficiency of up to 33.90%.
- The CQD layer on the U-shape device lasts 1321 minutes under high current, compared to 39 minutes in traditional designs.
- Low-temperature measurements show improved external quantum efficiency due to reduced non-radiative recombination.

## Abstract

A special micro LED whose light emitting area is laid out in a U-like shape is fabricated and integrated with colloidal quantum dots (CQDs). An inkjet-type machine directly dispenses the CQD layer to the central courtyard-like area of this U-shape micro LED. The blue photons emitted by the U-shape mesa with InGaN/GaN quantum wells can excite the CQDs at the central courtyard area and be converted into green or red ones. The U-shape micro LEDs are coated with Al2O3 by an atomic layer deposition system and exhibit moderate external quantum efficiency (6.51% max.) and high surface recombination because of their long peripheries. Low-temperature measurement also confirms the recovery of the external quantum efficiency due to lower non-radiative recombination from the exposed surfaces. The color conversion efficiency brought by the CQD layer can be as high as 33.90%. A further continuous CQD aging test, which was evaluated by the strength of the CQD emission, under current densities of 100 A/cm2 and 200 A/cm2 injected into the micro LED, showed a lifetime extension of the unprotected CQD emission up to 1321 min in the U-shape device compared to a 39 min lifetime in the traditional case, where the same CQD layer was placed on the top surface of a squared LED.