Structural, optical and electrical properties of chemically grown Pb1−xFexSe nanoparticle thin films

Single phase Pb1−xFexSe ( 0.00 ≤ x ≤ 0.07 ) thin films, with typical rocksalt structure, are grown by the chemical bath deposition method. An additional segregated phase of Fe2O3 is observed in the x ≥ 0.08 films. The average grain size in the films grown at a fixed bath temperature ( T b ) is observed to remain constant with increase in Fe concentration from x = 0.00 to x = 0.07 . A decrease in T b , for fixed x, results in a decrease in grain size in the films. The T b induced decrease in grain size is seen to result in an increase of direct optical band gap ( E g ) in films with the same x . In the typical case of x = 0.06 films, decrease in grain size from 9 nm to 3 nm due to change in T b from 85 to 55 ∘C, results in an increase in E g from 2.09 eV to 2.89 eV. The blue shift is attributed to enhanced quantum confinement in the nanograins. However, at a fixed T b , while grain size remains constant with increase in x , E g is observed to decrease. E g is seen to decrease from 2.20 to 1.84 eV with change in x from 0.02 to 0.07 in T b of 85 ∘C films. This decrease is attributed to tailoring of E g due to alloying between PbSe ( E g bulk = 0.28 eV ) and FeSe ( E g bulk = 0.14 eV ) in the single-phase nanoparticle films of Pb1−xFexSe. Resistivity decreases while Hall mobility increases with the increase in x ( 0.00 ≤ x ≤ 0.06 ) in the films.