A team led by Professor Meng Guodong at Xi'an Jiaotong University has built a phototransistor from a two-dimensional semiconductor that reaches high sensitivity and fast response without any applied gate voltage. The work, from the university's School of Electrical Engineering and its State Key Laboratory of Electrical Insulation and Power Equipment, was published as a front-cover paper in Advanced Optical Materials under the title Plasmon-Enhanced Photodetection in Ferroelectric-Tunable Two-Dimensional Phototransistor. PhD student She Junyi is the first author.
The target application is optical detection of partial discharge in power equipment. As insulation degrades in switchgear and gas-insulated switchgear, partial discharge in the early stages can emit faint ultraviolet-to-visible light. Optical sensing resists electromagnetic interference and carries spectral information, but the signals are weak. Two-dimensional materials such as tungsten disulfide (WS2) interact strongly with light, yet devices built from them have struggled with low conversion efficiency, a trade-off between gain and speed, and leakage and power draw from the gate voltage normally needed to tune them.
The team attacked these limits with two mechanisms. A WS2 channel sits on an ultrathin aluminum-doped hafnium oxide ferroelectric film about 10 nanometers thick, which serves as the gate dielectric. Above the channel, an array of gold nanoparticles, sized through simulation to maximize light-field enhancement, acts as a plasmonic layer. When light excites plasmon resonance, the nanoparticles concentrate the local field to generate more photocarriers and inject hot carriers that add photoconductance. The ferroelectric layer's remanent polarization replaces an external gate voltage, tuning carrier concentration and the contact barrier at zero bias, while lowering the interface barrier to speed up carrier transport.
At zero gate voltage, the device reached a specific detectivity of 1.36 × 10¹⁴ Jones, a measure of how weak a light signal it can pick up, and a response time of 9.51 milliseconds. Because no voltage is needed to hold the gate, the design also avoids the standing power cost of conventional gate-tuned devices.
The university says the results provide technical support for low-power sensing units and high-sensitivity sensor arrays for discharge detection. The work remains a single laboratory device. Moving to arrays and integrating them with online monitoring systems will still require validation of material uniformity and long-term reliability.
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