Back-Gated WS2-Enhanced Barium Titanate Phototransistor with Polarization-Controlled UV Responsivity and Enhanced Thermal Stability.

A high-performance ultraviolet (UV) phototransistor was developed utilizing a WS2/barium titanate (BTO) heterostructure within a back-gated ferroelectric field-effect configuration. BTO nanoparticles, prepared via hydrothermal synthesis, were spin-coated onto a TiO2 layer, while monolayer WS2 was drop-cast between aluminum source/drain electrodes. The intrinsic ferroelectric field, approximately 60 kV/cm, facilitated polarization-induced carrier modulation, resulting in a low dark current of 12.3 pA without the need for an external gate bias. Ultraviolet-visible (UV-vis) spectroscopy confirmed a bandgap reduction from 3.32 eV for pure BTO to 3.13 eV for the WS2/BTO composite, enhancing UV-vis light absorption. Raman spectroscopy further affirmed the structural integrity of WS2 postintegration. The integration of WS2 led to a decrease in the coercive field from 40 to 20 kV/cm, and a reduction in remanent polarization from 2.5 to 2.0 μC/cm2, indicating more efficient polarization switching. Photocurrent measurements under cyclic poling demonstrated a significant 28-fold enhancement, with the current increasing from 0.8 to 22.5 μA, and a peak responsivity of 38.5 A/W was achieved. The device exhibited a rapid rise time of 0.8 s, maintained a switching ratio exceeding 104, and demonstrated stable operation across a temperature range of 40-80 °C. These findings indicate the strong promise of WS2/BTO heterostructures for energy-efficient, polarization-modulated UV photodetection, suitable for applications in memory devices, optical sensors, and wearable electronics.