High-Quality Semiconductor Enhances SWIR Sensor Performance

SWIR sensors deliver clear visual information even in low-light conditions and can detect IR light that is both reflected and directly emitted by objects.

IR sensors use semiconductors to detect light signals and convert them into electrical signals. SWIR sensors typically use compound semiconductor materials, which have significantly higher electron mobility than single-element silicon semiconductors. The enhanced mobility provided by compound semiconductors allows even faint light signals to be detected with superior energy efficiency.

To advance the use of SWIR sensors for a range of applications, researchers at the Korea Research Institute of Standards and Science (KRISS) developed a high-quality compound semiconductor material for achieving ultrasensitive SWIR sensing.

The new material addresses the challenges posed by using indium gallium arsenide (InGaAs), the compound semiconductor that is most frequently used for SWIR sensors. The hurdles to successful use of InGaAs can include lattice mismatch during fabrication, high production costs, and intrinsic material limitations.

(a) Schematic structures of InGaAs/InAsP(Sb) multiple quantum well (MQW) LEDs, monolithically grown InP substrate using compositionally step-graded n+-InAsyP1-y buffers. (b) Calculated energy band structures of InGaAs/InAsP(Sb) MQW LEDs under zero bias at 300 Kelvin. Magnified view of the conduction band structure for (c) InGaAs/InAsP MQWs and (d) InGaAs/InAsPSb MQWs, representing the ground-state electron density profile. Courtesy of Advanced Functional Materials (2024). DOI: 10.1002/adfm.202406355.

The KRISS team developed an indium arsenide phosphide (InAsP) material, grown on an InP substrate, to serve as the light-absorbing layer in SWIR sensors. Compared to InGaAs, InAsP exhibits lower noise-to-signal ratios at room temperature, improving reliability. Additionally, InAsP provides an expanded detection range — from 1.7 to 2.8 μm — without any loss in performance.

To mitigate lattice mismatch, the researchers introduced a metamorphic (i.e., lattice relaxation) layer into the material. The metamorphic structure gradually adjusts the ratio of arsenide (As) and phosphide (P) between the substrate and the light-absorbing layer and serves as a buffer, preventing direct interaction between materials with different lattice properties. As a result, lattice strain is reduced, helping to ensure a high-quality material, and enabling flexible bandgap adjustments.

The researchers used metaphoric indium arsenide phosphide antimonide (InAsPSb) multiple quantum well (MQW) heterostructures to develop a 2.4-µm-wavelength LED. InAsPSb provides stronger electron and hole confinement compared to traditional InAsP-based MQW LEDs.

The team found that InAsPSb could effectively trap charge carriers within the MQW structure, preventing the charge leakage and efficiency degradation that has been observed in earlier InAsP-based devices. At the same time, InAsPSb ensured high stability levels under elevated temperatures. Consequently, the LEDs incorporating InAsPSb MQWs demonstrated minimal efficiency droop and stable light-emitting performance, even at high temperatures and high current densities.

To address the lattice constant mismatch of about 2% between the InAsPSb structures and the InP substrate, the researchers refined the metamorphic lattice relaxation growth technique to suppress threading dislocations caused by lattice mismatch.

The researchers were thus able to fabricate defect-free, high-quality LEDs within MQW structures containing InAsPSb. By minimizing the surface roughness of the LED device, they developed high-quality SWIR LEDs on InP substrates.

In addition to exhibiting an exceptionally low surface roughness of 1.1 nm, the resulting LEDs show well-defined, sharp interfaces within the heterostructures. The MQW LEDs also demonstrate favorable emission properties, including a low turn-on field, minimal efficiency droop, and stable emission wavelength across various injection currents. The electroluminescence peak wavelength of the MQW LEDs, characterized by a low turn-on voltage of about 0.15 V, demonstrates good stability at 15 Kelvin, even when the injection current density increases. The researchers attribute this stability to the strong carrier confinement within the MQW structure.

Solid-state IR sources designed to emit wavelengths above 2 µm frequently face challenges in achieving high emission efficiency, minimizing power consumption, and reducing fabrication costs. The development of InAsP is a significant step toward improving the efficiency and performance SWIR emitters.

InAsPSb-based LEDs could be used for advanced applications requiring high-efficiency IR emitters, including sensors for life science, optical communications, optical inspection, and medical diagnostics. While SWIR sensors have traditionally been used in military equipment such as night vision devices, their use is now expanding into diverse fields such as autonomous vehicles, semiconductor process monitoring, and smart farm cameras for observing plant growth.

“Given the challenges in importing compound semiconductor materials, which are classified as national strategic resources, it is imperative to secure independent technologies,” researcher Sang Jun Lee said. “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.”

The research was published in Advanced Functional Materials (www.doi.org/10.1002/adfm.202406355).