Bottom-up approaches to microLEDs emitting red, green and blue light based on GaN nanowires and relaxed InGaN platelets

Abstract

Miniaturization of light-emitting diodes (LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions, augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls. Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal-organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μm in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.

Cathodoluminescence investigations of dark-line defects in platelet-based InGaN nano-LED structures

“…This means that no material is wasted by etching away the layers in between the μ-LEDs. One such approach is to grow nanowires (NWs) using radial QWs as the emitting layer [20,21]. Despite their small size, the NWs can be used when larger pixels are needed as the size of a pixel can be scaled from a single NW to an array of NWs.…”

“…However, the a challenge is that radial QWs tend to vary in thickness and composition along the NW length [13]. It is also difficult to grow the NW core with a constant ternary (InGaN) composition and it may not even be possible to grow NWs [21].…”

Regular Red-Green-Blue InGaN quantum wells with In content up to 40% grown on InGaN nanopyramids

“…An EQE of 9% at 630 nm was achieved with axial nanowires [27]. InGaN based pyramid or truncated pyramids with a GaN seed layer demonstrated red emission for InGaN based QWs grown on the pyramid sidewalls [28] or grown on the c-plane facet of the InGaN core with In content of 18% [29] or 30% [30].…”