Chemical deposition of bismuth selenide thin films using N,N-dimethylselenourea

Good quality thin films of bismuth selenide of thickness up to 0.28 mu m were deposited from solutions containing bismuth nitrate, triethanolamine and N,N-dimethylselenourea maintained at temperatures ranging from room temperature to 40 degrees C. X-ray diffraction patterns of the samples annealed at 200 degrees C in air match the standard pattern of hexagonal Bi2Se3 (paraguanajuatite, JCPDS 33-0214). The films exhibit strong optical absorption corresponding to a bandgap of about 1.7-1.41 eV in the as-prepared films. These values decrease to about 1.57-1.06 eV upon annealing the films at 200 degrees C for 1 h in nitrogen. As-deposited, the films show high sheet resistance (similar to 10(12) Omega square(-1)) in the dark. Annealing the films in air or in nitrogen enhances the dark current by about seven orders of magnitude; the resulting dark conductivity is about 10 Omega(-1) cm(-1). This enhancement in conductivity results from improved crystallinity as well as from partial loss of selenium.