Advancing Silicon-Based InGaN Red Micro-LED Technology
In a recent collaboration between Fudan University and LatticePower, the research team published their findings on the application of silicon-based InGaN red Micro-LEDs for multicolor displays and high-speed visible light communication. Their work, titled “Red InGaN Micro-LEDs on Silicon Substrates: Potential for Multicolor Display and Wavelength Division Multiplexing Visible Light Communication,” was featured in the prestigious IEEE/OSA Journal of Lightwave Technology.
Challenges in Developing Red Micro-LEDs
Micro-LED technology is becoming increasingly vital for next-generation display systems, visible light communication, and optogenetics. However, developing red Micro-LEDs has been more challenging than creating GaN-based green and blue LEDs. Traditionally, red LEDs are made from AlInGaP materials, but these suffer from a marked efficiency drop when the chip size is reduced to the micron level. Additionally, AlInGaP materials are not compatible with the GaN-based green and blue LEDs used in most current systems. In contrast, InGaN materials, which can cover the entire visible spectrum by adjusting the indium content in the quantum wells, provide better mechanical stability and higher efficiency, making them more suitable for micron-scale red light emission.
The Promise of Silicon-Based InGaN Red Micro-LEDs
Most InGaN red Micro-LEDs are currently produced on patterned sapphire substrates or GaN pseudo-substrates grown on sapphire. This approach necessitates expensive laser lift-off processes to remove the native substrates for transfer printing in display technology. Silicon, however, offers a commercially attractive growth substrate due to its low cost, large-area availability, and high-quality wafers. Despite this potential, there has been limited research on silicon-based InGaN red Micro-LEDs and their performance in various applications.
Innovations in Multicolor Displays and Data Transmission
The team focused on developing silicon-based InGaN red Micro-LEDs to enable multicolor displays and multi-wavelength data transmission by examining wavelength and color shifts with increased current across different pixel sizes. They observed a significant shift from red to green wavelengths by varying pixel size and injected current. At a high current density of 100 A/cm², all pixel peak wavelengths exceeded 630 nm, suitable for high-current applications like augmented reality (AR) and virtual reality (VR). As current density increased, the CIE color coordinates shifted from red to green, achieving a broad color gamut. The team achieved uniform multicolor emission by modulating the duty cycle, showcasing the potential for multicolor Micro-LED displays on a single chip. Additionally, 80 μm pixels demonstrated an external quantum efficiency (EQE) of 0.19% at 2 A/cm² and 0.14% at 100 A/cm².
Breakthrough in Modulation Bandwidth for Visible Light Communication
Further testing revealed that silicon-based InGaN red Micro-LEDs smaller than 100 μm achieved modulation bandwidths greater than 400 MHz, making them highly suitable for data transmission. For 40 μm pixels, the maximum modulation bandwidths for red, yellow, and green emissions were 112.67 MHz, 126.38 MHz, and 533.15 MHz, respectively. The green emission bandwidth set a new record for tunable color Micro-LEDs, demonstrating significant potential for multicolor visible light communication.
A New Approach to Wavelength Division Multiplexing
The research team proposed a single-chip multicolor wavelength division multiplexing scheme, using different wavelength Micro-LEDs as transmitters for visible light communication. This approach achieved a maximum data transmission rate of 2.35 Gbps, marking the first report of silicon-based InGaN red Micro-LEDs being used in visible light communication. With high integration and miniaturization of pixels, this technology shows great promise for wearable communication devices and smartwatches, potentially simplifying future system integration.
Paper Link:
https://doi.org/10.1109/JLT.2023.3261875
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