Growth Control of Cu2-xS Films for Visible-Near Infrared Photodetectors

Abstract

Nanostructured plasmonic copper sulfide (Cu_2-xS), from the family of transition-metal sulfides with tunable optical and electrical properties, has drawn significant attention for broadband photodetectors in our research society. Herein, the attempt is made to grow Cu_2-xS films via sulfurization of copper (Cu) films through the chemical vapor deposition (CVD) technique at different sulfurization temperatures (200–400 °C). A hexagonal structured CuS phase is observed for the film grown at 300 °C, with a higher crystalline nature confirmed through structural analysis. Surface compositional analysis suggests that the film deposited at 300 °C exhibits more copper vacancies, which shows the greater diffusion of sulfur atoms into copper films, which leads to the formation of well-aggregated nanospheres with larger grains over the film’s surface. Moreover, the band gap of the grown films is observed in the range of 1.79–1.92 eV, and the localized surface plasmon resonance (LSPR) band is observed in the near-infrared (NIR) region through optical studies, which confirms the plasmonic nature of Cu_2-xS. Furthermore, the photodetector properties of the Au/Cu_2-xS/Au test device are investigated in terms of photoresponsivity (R_λ), specific detectivity (D*), and external quantum efficiency (EQE) under visible and NIR light illuminations. The film grown at 300 °C exhibits superior results such as R_λ of 2.48 ± 0.02 A/W and 5.10 ± 0.02 A/W, D* of 3.02 ± 0.02 × 10¹² Jones and 6.21 ± 0.02 × 10¹² Jones, and EQE of 581 ± 5% and 646 ± 5% under visible (λ = 530 nm) and NIR (λ = 980 nm) light illuminations, respectively, with lower incident power density at a bias voltage of 3 V, which signify the potential of the fabricated test device in the broadband photodetectors.