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 s
odium selenosulfate or N,N-dimethylselenourea as a source of selenide ions.
X-ray diffraction (XRD) studies on the films obtained from baths using sod
ium selenosulfate suggest a cubic structure as in berzelianite, Cu2-xSe wit
h x = 0.15. Annealing the films at 400 degrees C in nitrogen leads to a par
tial conversion of the films to Cu,Se. In the case of films obtained from t
he baths containing dimethylselenourea, the XRD patterns match that of kloc
kmannite, 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 c
arrier absorption in the near infrared region with absorption coefficient o
f 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, a
s 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.