In the present work, structural, microstructural, compositional and electronic band gap properties of As 40 Se 60 and As 40 Bi 15 Se 45 bulk and thin films are reported. The films were prepared by thermal evaporation technique under high vacuum. X-ray diffraction (XRD) study indicated amorphous nature of As 40 Se 60 in bulk prepared by melt quenching technique. Bi incorporation in As 40 Se 60 with composition Bi 15 As 40 Se 45 however led to nucleation of Bi 2 Se 3 nanocrystallites in the

more »

... ous matrix of As 40 Se 60 . The films made out of the two targets of composition As 40 Se 60 and As 40 Bi 15 Se 45 did not show any XRD peak, indicating their amorphous nature. UV-Visible-NIR spectroscopic study indicated a large decrease in the electronic band gap from 1.74 eV in films of composition As 40 Se 60 to 1.28 eV for compositon Bi 15 As 40 Se 45 . This decrease is explained on the basis of a high concentration of defect states leading to the presence of localized states in the band gap due to Bi incorporation. Field emission scanning electron microscopy (FESEM) images show smooth and homogeneous surface for the As 40 Se 60 films, while Bi incorporation led to increases of the surface roughness in the Bi 15 As 40 Se 45 films. The decreased band gap and increased surface roughness on Bi incorporation in As 40 Se 60 films indicate the suitability of these films for solar cell applications.