Phase-Engineered PtSe₂-Layered Films by a Plasma-Assisted Selenization Process toward All PtSe₂-Based Field Effect Transistor to Highly Sensitive, Flexible, and Wide-Spectrum Photoresponse Photodetectors

The formation of PtSe₂-layered films is reported in a large area by the direct plasma-assisted selenization of Pt films at a low temperature, where temperatures, as low as 100 °C at the applied plasma power of 400 W can be achieved. As the thickness of the Pt film exceeds 5 nm, the PtSe₂-layered film (five monolayers) exhibits a metallic behavior. A clear p-type semiconducting behavior of the PtSe₂-layered film (≈trilayers) is observed with the average field effective mobility of 0.7 cm² V⁻¹ s⁻¹ from back-gated transistor measurements as the thickness of the Pt film reaches below 2.5 nm. A full PtSe₂ field effect transistor is demonstrated where the thinner PtSe₂, exhibiting a semiconducting behavior, is used as the channel material, and the thicker PtSe₂, exhibiting a metallic behavior, is used as an electrode, yielding an ohmic contact. Furthermore, photodetectors using a few PtSe₂-layered films as an adsorption layer synthesized at the low temperature on a flexible substrate exhibit a wide range of absorption and photoresponse with the highest photocurrent of 9 µA under the laser wavelength of 408 nm. In addition, the device can maintain a high photoresponse under a large bending stress and 1000 bending cycles.