'Solar-blind' 2D heterostructure delivers 422-fold responsivity gain for UV sensing

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Artist's illustration of MnPS3 (purple) – WS2 (dark blue) photodetector device under microbeam UV (325 nm) laser characterization to map the dynamics of electrons (red) and holes (turquoise) when irradiation at different points of the heterostructure device. Credit: Poh Eng Tuan

Photodetectors remain a critical component in the development of advanced electronics and photonics, particularly in the role of signal readout through the conversion of photons into electrons. These digital imaging components are ubiquitous in sensors, cameras, adaptive displays, telecommunications, LiDAR systems, health monitoring wearables, and oximeters.

In the quest toward the next generation of optoelectronic devices, the spotlight lands upon ultrathin 2D materials with improved performance for integrated circuits and wearable electronics. In a recent study published in ACS Applied Electronic Materials, a team of researchers led by Haizhao Zhi and Eng Tuan Poh introduced a series of wide bandgap 2D materials—transition metal thio(seleno)phosphates into the light.

The team focused on manganese thiophosphate (MnPS3), a wide-bandgap semiconductor that is naturally "solar-blind," meaning it is highly sensitive to UV light while remaining transparent to much of the visible spectrum. While MnPS3 is an excellent candidate for UV sensing, its performance as a standalone material is often limited by low carrier mobility—it acts almost like a "near-perfect insulator."

To overcome this, the researchers engineered a van der Waals heterojunction by stacking monolayer WS2 (a more conductive semiconductor with a narrower bandgap) upon multilayer MnPS3. The results were nothing short of a "considerable leap."

By integrating these two materials, the team observed a 422-fold increase in responsivity and a 129-fold improvement in detectivity compared to the pristine MnPS3 device.

More interestingly, the researchers subsequently used a focused laser spot of only 1 micrometer in diameter to study the photocarrier dynamics in the device by "scanning" the laser across the heterojunction.

Rather than illuminating the entire device as per typical optoelectronic characterization, the single-spot scan allowed them to monitor the evolving trend in the photocurrent dynamics as the laser moved from the MnPS3 side, across the heterojunction interface, and onto the WS2 side.

Characterization of the photoresponse at different locations on the multilayered MnPS3−WS2 photodetector. (a). The OM picture of the vertical MnPS3−WS2 heterostructure photodetector. (b). The photocurrent as a function of time and different locations on the MnPS3−WS2 heterostructure photodetector. We shift the time function of the photocurrent (I−t curve) measured on different locations in the figure to make the results more discernible. Between d, e, f, and c, the vertical shift scale is 0.01 nA; moreover, the vertical shift scale of the I−t curve between f and c is 0.04 nA. (c). Band diagram of the MnPS3−WS2 heterojunction photodetector at a +1.5V bias with laser irradiation at positions c and f. (d). Band diagram of the MnPS3−WS2 heterojunction photodetector at a +1.5V bias with laser irradiation at position d. (e). Band diagram of the MnPS3−WS2 heterojunction photodetector at a +1.5 V bias with laser irradiation at positions a and e. (f). Band diagram of the MnPS3−WS2 heterojunction photodetector at +1.5V bias with laser irradiation at position b. Credit: Poh Eng Tuan

Across various positions of the heterostructure, the disparate band alignments and, consequently, the varying extents of a built-in internal electric field account for effective charge separation and the differing photocurrent responses. The resultant effect not only boosts the signal amplitude but also significantly reduces the extent of noise for improved sensitivity.

In parallel, the researchers also evaluated MnPSe3, the selenophosphate counterpart of MnPS3, revealing its broadband detection capability with a 3.6-fold magnitude increase in the corresponding MnPSe3—WS2 device.

The implications of this work extend beyond simple photodetection. As we move toward wafer-scale integration of 2D materials, understanding these localized carrier dynamics is crucial for developing high-speed, high-efficiency devices for telecommunications, environmental monitoring, and even deep-space imaging.

The continual evaluation of the performance of ultrathin 2D materials and their heterostructures could pave the way for next-generation advanced photonics and electronics that are not only thinner but vastly more powerful.

This story is part of Science X Dialog, where researchers can report findings from their published research articles. Visit this page for information about Science X Dialog and how to participate.

More information

Haizhao Zhi et al, Microbeam Laser Characterization in MnPS3(MnPSe3)–WS2Wide-Bandgap Semiconductor Heterojunction Photodetectors, ACS Applied Electronic Materials (2026). DOI: 10.1021/acsaelm.6c00417

Key concepts

2-dimensional systemsFunctional materialsSemiconductors

Dr. Poh Eng Tuan is a Research Fellow at the National University of Singapore, Department of Physics. He received his B.Sc. degree (Highest Distinction) in Chemistry and his Ph.D. degree in Integrative Sciences and Engineering from the National University of Singapore. His research experience spans multiple domains, with a focus on the optical functionality of 2D materials and their associated heterostructures. His current interests in advanced materials and non-linear optics include novel anisotropic 2D materials and 0D upconversion nanoparticles.