The Size-Dependent Photonic Characteristics of Colloidal-Quantum-Dot-Enhanced Micro-LEDs.

Colloidal CdSe/ZnS quantum dots (QD) enhanced micro-LEDs with sizes varying from 10 to 100 μm were fabricated and measured. The direct photolithography of quantum-dot-contained photoresists can place this color conversion layer on the top of an InGaN-based micro-LED and have a high throughput and semiconductor-grade precision. Both the uncoated and coated devices were characterized, and we determined that much higher brightness of a QD-enhanced micro-LED under the same current level was observed when compared to its AlGaInP counterpart. The color stability across the device sizes and injection currents were also examined. QD LEDs show low redshift of emission wavelength, which was recorded within 1 nm in some devices, with increasing current density from 1 to 300 A/cm. On the other hand, the light conversion efficiency (LCE) of QD-enhanced micro-LEDs was detected to decrease under the high current density or when the device is small. The angular intensities of QD-enhanced micro-LEDs were measured and compared with blue devices. With the help of the black matrix and omnidirectional light emission of colloidal QD, we observed that the angular intensities of the red and blue colors are close to Lambertian distribution, which can lead to a low color shift in all angles. From our study, the QD-enhanced micro-LEDs can effectively increase the brightness, the color stability, and the angular color match, and thus play a promising role in future micro-display technology.