Synthesis and Characterization of Bismuth Selenide and Copper Doped Bismuth Selenide Thin Films by Chemical Bath Deposition

BiySez and CuxBiySez thin films were grown on glass substrates by chemical bath deposition technique at room temperature with up to 24 hours deposition period. The films were deposited from stagnant solutions containing bismuth nitrate (4.16 g/L) complexed with tri-ethanolamine, sodium selenosulfate, and copper nitrate. The bath composition and deposition time were optimized in order to obtain sufficiently thick and crack-free layers for electrical measurements. Four various batches of samples, namely A, B, C, and D which were prepared by varying the chemical bath composition of Selenium (A, and D) or Copper sources (B, and C). The films' thickness is measured by Dektak surface profilometer. X-Ray diffraction (XRD)theta/2 theta technique was applied to study the structure of the films, and Electron Probe Micro-Anayser (EPMA) was utilized to investigate the films chemical composition. Atomic Force Microscopy (AFM) was used to examine the films topography and to determine the root-mean-square (RMS) surface roughness. The electrical properties of the films were determined by Hall Effect (HE) measurement technique. X-ray diffraction patterns of the as-deposited films had indicated that the films contain rhombohedral structure of Bi2Se3 phases. The RMS film surface roughness was about 30.4 nm and 17.8 nm for CuxBiySez films deposited for 24 hours in baths B and C, respectively. Crack free layers were observed for films deposited in bath A, B, and C. The composition for films deposited for 24 hours in bath B and C was Cu7.55Bi36.04Se56.41 and Cu5.28Bi37.79Se56.93, respectively. Higher copper content was obtained in films deposited in bath B compared to bath C. Electrical properties for an annealed BiySez film deposited in bath A for 24 hours indicated that the film is a n-type semiconductor and the main charge carriers are electrons with an average density of 1.7093x10(+19) /cm(2) and an average mobility of 1.54 cm(2)/V-s.