Being able to see light and detect radiation is of utmost importance at any frequency. While this challenge has been solved in the visible range, radiation detectors in the far-infrared and terahertz regimes are either not sensitive, slow, or require bulky and expensive, often cryogenically cooled devices, which hinders practical applications.
A recent study reported in Advanced Photonics combines quantum physics with a carefully designed metasurface to develop a compact detector that improves how THz radiation is captured and converted into an electrical signal.
At the core of the device is the in-plane photoelectric effect, a quantum process in which incoming THz photons transfer energy to electrons confined in a two-dimensional electron gas. The electrons move across a small, engineered potential step and generate a measurable current. Unlike conventional photoelectric detectors, this process does not require photons above a threshold energy and operates entirely within the plane of the material, avoiding key efficiency limits of earlier approaches.
Earlier detectors based on this effect demonstrated promising sensitivity but captured only a small fraction of incoming radiation because they relied on single antenna elements. The new work addresses this limitation by building the detector around a metasurface—a patterned layer that concentrates electromagnetic fields into subwavelength regions. In the reported device, a repeating “brickwork” structure both collects incoming radiation and directs it into narrow gaps where detection occurs.
Crucially, each of these gaps acts as an individual detection element. By arranging many such elements across the surface and connecting them electronically, the device combines their output into a single, stronger signal. This avoids the need for external optics or complex arrays and ensures that radiation is concentrated only where it contributes to detection.
The design follows a “top-down” approach that begins with the metasurface layout. Individual photoelectric tunable-step (PETS) detection elements are then embedded into the capacitive gaps, where the electromagnetic field is strongest. “This ensures optimal coupling of the metasurface to the detection elements,” notes corresponding author Wladislaw Michailow , who led the research at the University of Cambridge and later at Swansea University in the UK. “Compared to the conventional approach of connecting multiple devices in parallel, this approach allowed us to significantly boost the detection sensitivity,” adds Michailow. The strategy differs from earlier designs by treating light collection and detection as a single, integrated problem rather than separate components.
To refine the device, the researchers used simulations to optimize key structural parameters, such as the spacing of the repeating units and the gap size. These parameters control how strongly the electric field is confined and thus how much photocurrent is generated. The final design balances field enhancement with the width of the electron channel to maximize the measurable signal.
The detector was fabricated using a semiconductor structure that hosts a high-mobility electron gas, with fabrication steps similar to those used in field-effect transistor manufacturing. This compatibility provides a clear path toward integration into electronic circuits. Because the metasurface itself handles radiation confinement, the device does not require external focusing optics such as silicon lenses, which simplifies assembly and makes the concept suitable for large-scale production.
In experiments, the device was cooled to 10 K and illuminated with radiation near 1.9 THz. It produced a clear electrical response that followed the on–off pattern of the incoming signal.
From the measurements, the researchers calculated a responsivity of 2.7 amperes per watt. Their first proof-of-concept device also achieved an external quantum efficiency of 2.1 percent at 1.9 THz, representing about a 20-fold improvement over previously demonstrated PETS detectors. These gains stem largely from the metasurface design, which captures a greater portion of the incoming radiation and concentrates it in the active regions.
The device operates at zero source–drain bias, which reduces noise by avoiding dark currents. “The devices are direct detectors operating at zero bias, and therefore, they operate without dark currents,” observes first author Ruqiao Xia, who fabricated and measured the devices as part of her doctoral research in the Semiconductor Physics Group at the Cavendish Laboratory of the University of Cambridge. Because the geometry can be scaled, the same concept can be adapted to different parts of the electromagnetic spectrum, from microwave to mid-infrared frequencies.
Beyond sensitivity, the design also offers practical advantages. The planar structure is compatible with standard semiconductor processing and can be integrated with on-chip electronics. The use of flat metasurfaces removes the need for precise alignment of external components, simplifying packaging and deployment compared with conventional THz systems.
The researchers also point to the potential for operation at higher temperatures than many competing technologies. PETS detectors based on similar materials have shown performance at temperatures accessible with compact cryocoolers, rather than requiring liquid helium. This opens a temperature range that sits between highly sensitive cryogenic detectors and lower-sensitivity room-temperature devices, which could expand the range of practical applications.
The work represents the first demonstration of a quantum metasurface photodetector based on a two-dimensional electron system. It marks a step forward in efforts to bridge the THz gap by combining efficient light capture with a high-sensitivity quantum detection mechanism. “The results are particularly intriguing due to the applications that terahertz technology can enable, in areas such as wireless network, healthcare, astronomy, biomedicine, quality assurance in manufacturing, and many others,” remarks coauthor David Ritchie , head of the Semiconductor Physics Group.
By integrating metasurface optics directly into the detector, the study shows how advances in materials design and quantum physics can address long-standing limitations in terahertz technology.
For details, read the original Gold Open Access article by R. Xia et al., “ Quantum metasurface-based photoelectric tunable-step terahertz detector ,” Adv. Photon . 8(2), 026011 (2026), doi: 10.1117/1.AP.8.2.026011
Advanced Photonics
Quantum metasurface-based photoelectric tunable-step terahertz detector
17-Mar-2026