Strain- vs. band-engineering in PbSe thin films: A comparative DFT and experimental study of ca and Sn doping for tailored infrared optoelectronics

Despite the promising role of lead selenide (PbSe) in mid-infrared detection, a mechanistic understanding of how specific cationic doping tailors its optoelectronic properties is still lacking. To fill this gap, we employed the chemical bath deposition method (CBD) to fabricate PbSe films doped with calcium and tin. Through simulation calculations and sample characterization, we investigated the effects of the dopant type and concentration on the performance of the PbSe films. The study reveals a clear superiority of Sn over Ca as a functional dopant. We find that a Sn:Pb ratio of 1:7 yields the optimal combination of a narrow bandgap (0.284 eV), the lowest microstrain (0.12%), and the strongest infrared absorption. XPS results elucidate the chemical states of dopants, revealing Sn 4+ substitution and Ca-induced oxide/selenide formation, which correlate with their divergent optoelectronic behaviors. Collectively, these results establish strategic Sn doping as a highly effective route for tailoring PbSe films toward high-sensitivity mid-infrared detection.