Researchers from Xi'an Jiaotong University have developed a phototransistor based on a two-dimensional semiconductor that demonstrates high sensitivity and fast response without the need to apply voltage to the gate. This development was published in the journal Advanced Optical Materials under the title 'Plasmon-Enhanced Photodetection in Ferroelectric-Tunable Two-Dimensional Phototransistor.'
The work, conducted by the School of Electrical Engineering and the State Key Laboratory of Electrical Insulation and Power Equipment of the university, aims at the optical detection of partial discharges in power equipment. During the degradation of insulation in switching and gas-insulated switching apparatuses, weak ultraviolet or visible light emissions can occur in the early stages.
Optical probing allows for the avoidance of electromagnetic interference and the transmission of spectral information, but the resulting signals are very weak. Although two-dimensional materials such as tungsten disulfide (WS2) interact strongly with light, devices based on them have faced issues with low conversion efficiency, a trade-off between gain and speed, as well as leakage and power consumption typically associated with the gate voltage required to tune such devices.
The team overcame these limitations using two mechanisms. The WS2 channel is placed on an ultra-thin aluminum-doped hafnium oxide ferroelectric film, approximately 10 nanometers thick, which serves as the gate dielectric. An array of gold nanoparticles, whose size was determined through modeling for maximum light field enhancement, is placed above the channel and functions as a plasmonic layer.
When light excites the plasmonic resonance, the nanoparticles concentrate the local field, leading to the generation of more photocarriers and the injection of hot carriers, which increases photoconductivity. The residual polarization of the ferroelectric layer replaces the external gate voltage, tuning the carrier concentration and contact barrier at zero bias while simultaneously lowering the interface barrier for accelerated carrier transport.
At zero gate voltage, the device achieved a specific detectability of $1.36 imes 10^{14}$ Jouns, indicating its ability to capture weak light signals, as well as a response time of 9.51 milliseconds. Since no voltage is required to maintain the gate, this design also eliminates the constant energy costs characteristic of traditional gate-tunable devices.
The university notes that the results obtained could serve as a technical basis for developing low-power sensor modules and highly sensitive detector arrays for discharge detection. However, currently, this is a single laboratory device, and transitioning to arrays and integrating them with online monitoring systems will require verification of material uniformity and long-term reliability.