Researchers from the Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, report self-powered far-UVC photodetectors based on cubic-phase MgZnO (c-MgZnO) in ACS Applied Materials & Interfaces. The team realized two device types—a Schottky junction and a PIN heterojunction—that operated at zero bias with nanosecond response and stable performance at high temperature.

Far-UVC (200–240 nm) sensing is sought for sterilization oversight, arc-discharge monitoring, aerospace instrumentation, and power-limited field systems. Wide-bandgap materials are essential because they absorb far-UVC while rejecting longer wavelengths, and self-powered device architectures reduce energy demand by using built-in electric fields rather than external bias. Prior studies highlighted these advantages for next-generation UV detection and framed the need for far-UVC sensors that combine selectivity with low power consumption.

In response, the group designed two self-powered stacks using c-MgZnO as the absorber: a Pt/c-MgZnO/ZnO Schottky photodiode and a NiO/c-MgZnO/ZnO PIN heterojunction. To cut optical loss in the deep-UV, both devices used a mesh-structured platinum top electrode. The PIN design added an ultrathin p-NiO layer (~30 nm) to increase the built-in potential and extend the effective space-charge region. The process followed standard thin-film steps: ZnO templates were grown by molecular beam epitaxy, c-MgZnO was deposited on top, and contacts were defined by sputtering and lithography. These choices balanced transmission in the far-UVC with electrical robustness and thermal durability.

The operating principle centered on photocarrier generation in c-MgZnO and drift collection by depletion fields. Under illumination, far-UVC photons created electron–hole pairs in the c-MgZnO layer; interfacial fields at the Schottky barrier or across the PIN junction then separated and swept carriers to the electrodes, enabling zero-bias operation. The authors further supported this mechanism with band-alignment measurements using ultraviolet photoelectron spectroscopy and explained why the PIN architecture collects carriers more efficiently: the built-in field spans the active layer, reducing diffusion losses that can limit a Schottky structure.

Performance at room temperature demonstrated three strengths. First, spectral selectivity: both devices peaked near 222 nm while strongly rejecting longer-wavelength light, consistent with intrinsic far-UVC absorption in c-MgZnO. Second, speed: time-resolved tests recorded ~30 ns rise and ~450 ns decay at zero bias, with the decay governed by the external RC constant rather than slow trapping—favorable for fast sensing. Third, responsivity and detectivity: the Schottky device reached ~0.36 mA/W at 222 nm, whereas the PIN device achieved ~3.43 mA/W and a specific detectivity D* of ~3.07 × 10¹² Jones, roughly two orders of magnitude above the Schottky diode.

Thermal tests addressed deployment in harsh environments. Under repeated on/off cycling at 200 °C and zero bias, both devices maintained stable photoresponse over extended intervals, indicating reliable operation. With temperature increase, responsivity rose markedly—most prominently in the PIN device—consistent with enhanced absorption and more effective carrier transport across its extended depletion region. At 200 °C, the PIN photodiode typically reached ~96 mA/W responsivity and ~1.21 × 10¹² Jones detectivity, while the Schottky device remained lower. Dark-current measurements under reverse bias also showed the PIN structure held more than an order of magnitude lower current than the Schottky device across the temperature range.

The research process followed established, scalable thin-film methods rather than exotic steps. Films exhibited high crystallinity and smooth surfaces; ohmic contacts were confirmed on constituent layers; and a mesh platinum electrode was selected for its conductivity and chemical stability at high temperature. The authors summarized peer comparisons indicating that their c-MgZnO PIN device combined nanosecond-scale response with competitive responsivity and detectivity among self-powered far-UVC photodetectors, while also filling a material-system gap by advancing c-MgZnO for this band.

Taken together, the results suggest a practical route to compact, low-power far-UVC sensors. By pairing an ultrawide-bandgap absorber with a built-in-field architecture and deep-UV-compatible electrodes, the devices addressed three persistent bottlenecks—power consumption, signal speed, and thermal stability. Potential uses include sterilization monitoring, remote UV environmental surveillance, aerospace UV payloads, and industrial fault detection where external power and cooling are limited.