Copper selenide thin films by chemical bath deposition

We report the structural, optical, and electrical properties of thin films (0.05 to 0.25 mu m) of copper selenide obtained from chemical baths using sodium selenosulfate or N,N-dimethylselenourea as a source of selenide ions. X-ray diffraction (XRD) studies on the films obtained from baths using sodium selenosulfate suggest a cubic structure as in berzelianite, Cu2-xSe with x = 0.15. Annealing the films at 400 degrees C in nitrogen leads to a partial conversion of the films to Cu,Se. In the case of films obtained from the baths containing dimethylselenourea, the XRD patterns match that of klockmannite, CuSe. Annealing these films in nitrogen at 400 degrees C results in loss of selenium, and consequently a composition rich in copper, similar to Cu2-xSe, is reached. Optical absorption in the films result from free carrier absorption in the near infrared region with absorption coefficient of similar to 10(5) cm(-1). Band-to-band transitions which gives rise to the optical absorption in the visible-ultraviolet region may be interpreted in terms of direct allowed transitions with band gap in the 2.1-2.3 eV range and indirect allowed transitions with band gap 1.2-1.4 eV. All the films, as prepared and annealed, show p-type conductivity, in the range of (1-5) x 10(3) Omega(-1) cm(-1). This results in high near infrared reflectance, of 30-80%. (C) 1999 Elsevier Science B.V. All rights reserved.