Scientists innovate mid-infrared photodetectors for exoplanet detection, expanding applications to environmental and medical fields

KAIST (represented by President Kwang-Hyung Lee) announced on the 27th of March that a research team led by Professor SangHyeon Kim from the School of Electrical Engineering has developed a mid-infrared photodetector that operates stably at room temperature, marking a major turning point for the commercialization of ultra-compact optical sensors.

The newly developed photodetector utilizes conventional silicon-based CMOS processes, enabling low-cost mass production while maintaining stable operation at room temperature. Notably, the research team successfully demonstrated the real-time detection of carbon dioxide (CO₂) gas using ultra-compact and ultra-thin optical sensors equipped with this photodetector, proving its potential for environmental monitoring and hazardous gas analysis.

Existing mid-infrared photodetectors generally require cooling systems due to high thermal noise at room temperature. These cooling systems increase the size and cost of equipment, making miniaturization and integration into portable devices challenging. Furthermore, conventional mid-infrared photodetectors are incompatible with silicon-based CMOS processes, limiting large-scale production and commercialization.

To address these limitations, the research team developed a waveguide-integrated photodetector using germanium (Ge), a Group IV element like silicon. This approach enables broad-spectrum mid-infrared detection while ensuring stable operation at room temperature.

A waveguide is a structure designed to efficiently guide light along a specific path with minimal loss. To implement various optical functions on a chip (on-chip), the development of waveguide-integrated photodetectors and waveguide-based optical components is essential.

Unlike conventional photodetectors that primarily rely on bandgap absorption principles, this new technology leverages the bolometric effect*, allowing it to detect the entire mid-infrared spectral range. As a result, it can be widely applied to the real-time sensing of various molecular species.

*Bolometric effect: A principle in which light absorption leads to an increase in temperature, causing electrical signals to change accordingly.

The waveguide-integrated mid-infrared photodetector developed by the research team is considered a groundbreaking innovation that overcomes the limitations of existing mid-infrared sensor technologies, including the need for cooling, difficulties in mass production, and high costs.

This breakthrough technology is expected to be applicable across diverse fields, including environmental monitoring, medical diagnostics, industrial process management, national defense and security, and smart devices. It also paves the way for next-generation mid-infrared sensor advancements.

Professor SangHyeon Kim from KAIST stated, "This research represents a novel approach that overcomes the limitations of existing mid-infrared photodetector technologies and has great potential for practical applications in various fields." He further emphasized, "Since this sensor technology is compatible with CMOS processes, it enables low-cost mass production, making it highly suitable for next-generation environmental monitoring systems and smart manufacturing sites."

The study, with Dr. Joonsup Shim (currently a postdoctoral researcher at Harvard University) as the first author, was published on March 19, 2025 in the journal Light: Science & Applications.