Chemical deposition of bismuth selenide thin films using N,N-dimethylselenourea
Good quality thin films of bismuth selenide of thickness up to were deposited from solutions containing bismuth nitrate, triethanolamine and N,N-dimethylselenourea maintained at temperatures ranging from room temperature to . X-ray diffraction patterns of the samples annealed at in air match the standard pattern of hexagonal (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 for 1 h in nitrogen. As-deposited, the films show high sheet resistance 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 . This enhancement in conductivity results from improved crystallinity as well as from partial loss of selenium.