Progress towards microLED bandwidth and efficiency improvement

The first paper, titled ‘Parallel Communication with InGaN/GaN Micro-LEDs Using a CMOS Compatible Approach’, explores the development of LEDs on a 200mm silicon substrate. This breakthrough facilitates the production of a few-micron-sized LED matrices, each LED being individually managed by dedicated CMOS circuits. The presentation is scheduled for January 31^st, from 9:00 to 9:20am PST, at Moscone Centre, Room 2002, Level 2 West.

InGaN/GaN microLEDs are emerging as a robust option for high data-rate light communication, owing to their durability, scalability, and capability to achieve GHz bandwidth. Utilising these in an array format allows for parallel transmission, resulting in a high data-rate density. CEA-Leti has patented a process for integrating a GaN LED matrix over a CMOS ASIC. In this CMOS-compatible approach, microLEDs are optimally integrated by bonding them directly onto a 200mm silicon wafer, using GaN-based devices as both emitters and fast photodetectors.

Anthony Cibié, the lead author, explained: “In order to address communication applications, we modulate LEDs at high frequency to reach a high data rate. Our aim is to use an array of LEDs to emit light and to detect it by an array of photodiodes, both made from GaN. We know how to fabricate thousands of pixels arrays, thus we can have thousands of parallel communication channels.”

Efficiency improvement

CEA-Leti's second paper, ‘Influence of quantum well thickness on carrier diffusion length in InGaN quantum wells grown on sapphire, freestanding GaN, and Si’, presents a strategy to combat the efficiency drop in InGaN/GaN LEDs as pixel size decreases. This research, presented on January 30^th, from 9:20 to 9:40am PST at Moscone Centre, Room 2024 (Level 2 West), focuses on understanding and controlling carrier diffusion to improve efficiency.

Simon Litschgi, the paper's lead author, noted: “In this presentation, we show experimentally that the diffusion length can be reduced by decreasing the thickness of the InGaN quantum well, as the theory predicts. In addition, we present a power-dependent, unexpected behaviour of the diffusion observed in large quantum wells that may help us to understand the physics of the emitters.”

Litschgi highlighted that these phenomena were examined on various epitaxy substrates, including silicon, paving the way for more efficient GaN microLED devices on 200 and 300mm Si wafers. This approach is seen as the most cost-effective industrial solution for display and communication applications.

Laurent Fulbert, Deputy Head of CEA-Leti’s Optics and Photonics Division, commented: “As a leader in microLED technology, CEA-Leti has long-focused on developing cutting-edge display and light-communication systems that meet the needs of our business partners and help them shape the markets they serve. These two projects directly address the interests of our partners.”