Infrared sensors detect light in wavelengths invisible to the human eye and convert it into electrical signals, uncovering information previously beyond reach. Within the infrared spectrum, short-wave infrared (SWIR), covering wavelengths of 1.4–3.0 micrometers (μm), excels at penetrating smoke and fog while identifying unique spectral signatures of objects. These characteristics make SWIR indispensable for advanced industrial applications, including autonomous vehicle cameras and smart IoT sensors, where it acts as the system’s ‘eyes.’
The Korea Research Institute of Standards and Science (KRISS, President Ho Seong Lee) has successfully developed a high-quality compound semiconductor material for ultra-sensitive SWIR sensors.
SWIR sensors deliver clear visual information even in low-light conditions, detecting both infrared reflected off objects and that emitted directly by them. While traditionally used in military equipment such as night vision devices, SWIR sensors are now expanding into diverse fields, including autonomous vehicles, semiconductor process monitoring, and smart farm cameras for plant growth observation.
In infrared sensors, the semiconductor material plays a critical role in detecting light signals and converting them into electrical signals. SWIR sensors designed for advanced applications typically employ compound semiconductors—materials composed of two or more elements—due to their significantly higher electron mobility compared to single-element silicon semiconductors. This enhanced mobility allows for the detection of faint light signals with superior energy efficiency.
Currently, indium gallium arsenide (InGaAs), grown on an indium phosphide (InP) substrate, is the most commonly used compound semiconductor material for SWIR sensors. However, InGaAs-based materials face challenges such as lattice mismatch during fabrication and intrinsic material limitations, which hinder the development of high-performance SWIR sensors.
KRISS has addressed these challenges by developing a new indium arsenide phosphide (InAsP) material, grown on an InP substrate as the light-absorbing layer. Compared to InGaAs, InAsP exhibits lower noise-to-signal ratios at room temperature, improving reliability. Additionally, its detection range has been expanded from 1.7 μm to 2.8 μm without any loss in performance.
The key innovation lies in the introduction of a metamorphic (lattice relaxation) layer to mitigate lattice mismatch. The research team incorporated a metamorphic structure that gradually adjusts the ratio of As and P between the substrate and the light-absorbing layer. This structure serves as a buffer, preventing direct interaction between materials with differing lattice properties. As a result, lattice strain is significantly reduced, ensuring high material quality and enabling flexible bandgap adjustments.
Sang Jun Lee, Principal Researcher at the KRISS Semiconductor and Display Metrology Group, stated, “Given the challenges in importing compound semiconductor materials, which are classified as national strategic resources, it is imperative to secure independent technologies. The material we have developed is ready for immediate commercialization and is expected to be widely applied in emerging industries, including fighter jet radar systems, pharmaceutical defect inspection, and plastic recycling processes.”
This research was supported by the Ministry of Science and ICT’s Core Technology Development Program for Next-Generation Compound Semiconductors and was published in the esteemed journal Advanced Functional Materials (IF: 19) in February.
The research team developed InAsPSb, which provides significantly stronger electron and hole confinement compared to traditional InAsP-based multiple quantum well (MQW) LEDs. This advancement effectively traps charge carriers within the MQW structure, addressing issues of charge leakage and efficiency degradation observed in earlier InAsP-based devices, while ensuring high stability under elevated temperatures. Consequently, LEDs incorporating InAsPSb MQWs demonstrate minimal efficiency droop and stable light-emitting performance, even at high temperatures and high current densities.
To address the significant lattice constant mismatch (approximately 2.0%) between InAsPSb and the InP substrate, the researchers refined the metamorphic lattice relaxation growth technique. This approach effectively suppressed threading dislocations caused by lattice mismatch, enabling the fabrication of defect-free, high-quality LEDs within MQW structures containing InAsPSb. By minimizing the surface roughness of the LED device, the team successfully developed high-quality SWIR light-emitting devices on InP substrates.
With these innovative processes and material advancements, InAsPSb-based LEDs demonstrate significant potential as a groundbreaking solution for various advanced applications requiring high-efficiency infrared emitters. These applications include detection, life science sensors, optical communication, and medical diagnostics. In recognition of its contributions to the development of high-efficiency MQW LEDs, the study was published in Advanced Functional Materials on November 7, 2024.
