Electrical engineers at Duke University have built the fastest pyroelectric photodetector ever demonstrated, a device capable of detecting light across the entire electromagnetic spectrum and generating a signal in just 125 picoseconds. The findings appear in the journal Advanced Functional Materials.
The sensor operates at room temperature, requires no external power source, and is thin enough to integrate directly into on-chip systems. Potential applications span skin cancer detection, food safety monitoring, large-scale agriculture, and space-based sensing.
Why Conventional Detectors Fall Short
Most digital cameras rely on semiconductor photodetectors that respond only to visible light, much like the human eye. Detecting wavelengths outside that narrow band typically requires pyroelectric detectors, which produce an electrical signal by warming up after absorbing incoming light.
The problem is efficiency. Harder-to-capture wavelengths produce very little heat, so conventional pyroelectric detectors need either thick absorbing materials or intense illumination to function. Both requirements make the devices bulky and slow, since heat does not travel quickly through dense material.
“Commercial pyroelectric detectors aren’t very responsive, so they need a very bright light or very thick absorbers to work, which naturally makes them slow because heat doesn’t move that fast,” said Maiken Mikkelsen, professor of electrical and computer engineering at Duke. “Our approach cleverly integrates near-perfect absorbers and super-thin pyroelectrics to achieve a response time of 125 picoseconds, which is a huge improvement for the field.”
How the Metasurface Works
The Duke device uses a structure the team calls a metasurface. It consists of precisely arranged silver nanocubes placed on a transparent film positioned just 10 nanometers above a thin layer of gold.
When light strikes a nanocube, it excites the silver’s electrons, trapping the light’s energy through a process known as plasmonics. The specific frequency of light captured depends on the size of the nanocubes and the spacing between them, giving researchers direct control over which wavelengths the device absorbs.
Because this trapping mechanism is extremely efficient, only a very thin layer of pyroelectric material is needed beneath the structure to convert the absorbed energy into an electrical signal. Thin material means heat travels faster, and faster heat transfer means a faster response.
Mikkelsen’s lab first demonstrated the underlying concept in 2019, though that version was not designed to measure response speed. The results caught researchers off guard. “Thermal photodetectors are supposed to be slow, so this was mind-boggling to the entire community,” Mikkelsen said. “We were taken off guard that it seemed to be working on time scales similar to that of silicon photodetectors.”
Refining the Design
Eunso Shin, a PhD student in Mikkelsen’s laboratory, spent several years optimizing the device and developing a measurement method that does not rely on expensive external equipment. That work produced the current record-breaking version.
The combination of full-spectrum sensitivity, room-temperature operation, and a 125-picosecond response time places this detector in territory previously occupied only by semiconductor-based sensors, which are inherently blind to most of the electromagnetic spectrum. Whether the technology scales into commercial multispectral cameras will depend on further engineering work, but the underlying performance benchmark is now established.
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