A review on the low external quantum efficiency and the remedies for GaN-based micro-LEDs

Abstract

GaN-based micro-size light-emitting diode (μLED) have emerged as a promising light sources for a wide range of applications in displays, visible light communication etc. In parallel with the two key technological bottlenecks: full-color scheme and mass transfer technique that need overcoming, it is known that the low external quantum efficiency (EQE) is also another challenge for μLEDs from the perspective of manufacturing technology and device physics. The low EQE for GaN based μLEDs is opposite to the common belief for GaN-based LEDs, such that GaN based LEDs are featured with high quantum efficiency, mechanically robust and energy saving. Therefore, in this work, we have reviewed the origin for the low EQE for μLEDs. More importantly, we have also reported the underlying devices physics and proposed optimization strategies to boost the EQE for μLEDs. Our work is targeted to provide a guideline for the community to develop high-performance GaN-based μLEDs.

Designs of InGaN Micro-LED Structure for Improving Quantum Efficiency at Low Current Density

“…To address this issue, sidewall passivation using dielectric materials and wet etching using buffered hydrofluoric acid or photoelectrochemical method were proposed to minimize these effects to a certain level for the micro-LED [ 31 – 33 ]. However, even improved by the sidewall passivation, the peak EQE of micro-LEDs (with a size smaller than 60 μm) is still lower than 25%, and dramatically decreased to several percent at a current density lower than 2 A cm −2 [ 34 , 35 ]. Especially for the InGaN-based red micro-LED, the currently reported EQE is quite limited to lower than 1%, due to the strong polarization and poor crystal quality [ 36 ].…”

Cleanroom strategies for micro- and nano-fabricating flexible implantable neural electronics

“…Integration with external components such as power sources, resistors, transistors, diodes and so on is perhaps the greatest challenge due to the mismatch between properties, and their size. There is however progress with miniaturization and increasing efficiency of electronics devices such as µLEDs [ 79 ], which will be crucial for converting optogenetics from a tool for in-vivo animal neuroscience studies into a common medical treatment.…”

Magneto‐Optogenetic Deep‐Brain Multimodal Neurostimulation

“…There is also a trend of better light emission efficiency with decreasing size, as well the lack of "thermal droop" that causes a drop in optical power density larger μLEDs which are run at higher current densities. [65] There is certainly scope for an Blood-brain barrier.…”

“…There is also a trend of better light emission efficiency with decreasing size, as well the lack of “thermal droop” that causes a drop in optical power density larger μLEDs which are run at higher current densities. [ 65 ] There is certainly scope for an optimization of device parameters than would allow significant miniaturization. A complementary approach to address the heating issue would be to use magnetic microcoils to effectively drop the activation threshold required—this could significantly mitigate any heating issues.…”