Enhanced conductivity, photoresponse, and band-gap tuning of ZnSe thin films doped with In, Sn, and Sb

Zinc selenide (ZnSe) thin films were doped with different metals using thermal evaporation to enhance their electrical and optical properties for use in photovoltaic and optoelectronic devices. Eight potential metal dopants (Ag, Al, Au, Cu, In, Ni, Sb, and Sn) were initially chosen based on their ability to improve conductivity, ionic size compatibility with Zn²⁺ and Se^2-, and thermophysical properties, such as their melting point, vapor pressure, oxidation tendency, and evaporation behavior. Only films doped with In, Sn, and Sb exhibited good uniformity and desired surface reflectivity. These three films were analyzed for their structure, morphology, composition, electrical, and optical characteristics. All three films maintained the cubic zinc blende structure that is typical of ZnSe and showed homogeneous and smooth surfaces. Chemical analysis revealed that the elements were predominantly in a single-valency state except for Sn, which displayed a two-valency state. The dopants formed narrow layers adjacent to the substrate. Spectrophotometric measurements indicated red shift in the band-gap energy. The electrical conductivity increased by five orders of magnitude in all three doped films. Additionally, the films doped with In and Sb showed a positive photoresponse, while the Sn-doped film exhibited a negative photoresponse. These findings highlight the importance of selecting dopants based on their physical compatibility and suitability for deposition to produce high-quality doped ZnSe thin films.