KRISS develops new materials for SWIR sensors
The Korea Research Institute of Standards and Science (KRISS) 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.
Currently, InGaAs, grown on an InP substrate, is the most commonly used 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 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, said: “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 commercialisation and is expected to be widely applied in emerging industries, including fighter jet radar systems, pharmaceutical defect inspection, and plastic recycling processes.”
InAsPSb SWIR LEDs
The team has also developed InAsPSb, which provides 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, according to the team.
To address the significant lattice constant mismatch (approximately 2.0 percent) 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 minimising the surface roughness of the LED device, the team successfully developed high-quality SWIR light-emitting devices on InP substrates.
They believe that InAsPSb-based LEDs demonstrate significant potential for various advanced applications requiring high-efficiency infrared emitters including detection, life science sensors, optical communication, and medical diagnostics. The LED study 'Metamorphic InGaAs/InAsPSb Quantum Well Light Emitting Diodes for Operation in the Short-Wave Infrared Regionw' was published in Advanced Functional Materials in November 2024.
Pictured above :(left) principal researcher Byong Sun Chun ; (right) principal researcher Sang Jun Lee
