Centimeter-Scale Ultrathin Platinum Monosulfide Films with Large Negative Temperature Coefficient of Resistance for Deformable Visible-to-Mid-Infrared Photodetectors.

Broadband photodetectors covering a spectrum range of visible-to-mid-infrared (Mid-IR) are widely utilized for a range of applications, such as chemical sensing and medical devices. As their physical form factors evolve, a variety of photoresponsive electronic materials have been explored to adapt their demanded mechanical deformability. Herein, we report on a chemical vapor deposition (CVD) growth of centimeter-sized ultrathin (i.e., sub 10 nm) platinum monosulfide (PtS) films and their integration onto flexible polyimide (PI) substrates. Flexible devices composed of ultrathin PtS/PIs exhibit notable photoresponsiveness at a wide range of illumination wavelengths, i.e. visible spectra of 405 nm-to-940 nm to the mid-IR range of 4.6 μm, which is accompanied by a significant mechanical bendability. Furthermore, they exhibit temperature-variant transport characteristics of a p-type semiconductor involving a thermal generation of charge carriers; i.e., a significant increase of current with increasing temperature, yielding a large negativity of -0.62% °C^-1 for the temperature coefficient of resistance (TCR). The underlying mechanism for this mid-IR photoresponsiveness is attributed to the bolometric effect-driven carrier excitations facilitated by the midgap states of PtS films, as clarified through ultraviolet photoelectron spectroscopy (UPS) characterizations. Additionally, by leveraging the mechanical deformation-invariant photoresponsiveness, we demonstrate PtS/PI phototransistors able to biaxially stretch under modulated illuminations and gating conditions. This study is believed to offer opportunities for ultrathin semiconductors toward emerging photoelectronic devices with unconventional functionalities and configurations.

Duke Scholars

Author Tania Roy Electrical and Computer Engineering