Impact of copper concentration and post-deposition annealing cum controlled cooling on the photoresponsivity for Cu2SnSe3 (CTSe) thin films

Copper tin selenide, Cu₂SnSe₃ (CTSe), a ternary compound chalcogenide semiconductor material is gaining interest to be used as an optoelectronic material because of its high absorption coefficient, an optimal band gap ranging from 0.8 to 1.7 eV and preferable electrical properties (carrier concentration ̴ 10¹⁸–10²¹ cm⁻³ and hole mobility ̴ 2–870 cm²V⁻¹ s⁻¹). CTSe is an emerging semiconductor material having a wide array of applications including solar cell, photodetectors, and thermoelectric and supercapacitor applications. In the current research work, CTSe thin films were studied for the application of wavelength-selective photodetectors. The impact of copper concentration with subsequent annealing on the performance of photodetection was studied. Thermally evaporated thin films were prepared by taking Cu, Sn and Se powders (Alfa Aesar and Thomas Baker, 99.99% purity) in stoichiometric ratio of 2:1:3 and mixed together for pellet preparation. Post-deposition annealing cum controlled cooling was carried out at 400 °C and 450 °C in selenium environment. The deposited films showed Cu-poor composition with n-type conductivity. To maintain the stoichiometry, additional copper was deposited using DC sputtering at 100W power. Post deposition, the samples were reannealed in the same annealing cum controlled cooling profile. Compositional study confirmed an increase in the copper atomic % and a change in the conductivity to p-type from the previously obtained n-type. Interdiffusion of copper is playing a significant role in modifying the conductivity of the deposited samples. It was found that annealing modified the structural, electrical and optical properties of the samples. With the modified opto-electrical properties, the wavelength-selective photoresponse shows better performance.