Thin films of CdTe (rich Cd) covered with a thin layer of Zn were prepared by a thermal evaporation technique. The prepared samples were studied for different annealing temperatures (T-an) and for different intervals of time (t(an)). Spectral response investigations have been carried out and revealed the diffusion of Zn atoms into the CdTe films. The Zn diffusion length (L) and the corresponding diffusion coefficient (D) as a function of thermal annealing time (t(an)) were studied. At lower thermal treatment (T-an less than or equal to 100degreesC and t(an) less than or equal to 30 min.), a layer of CdZnTe mixed structure was formed, with a diffusion length in the interval of 0.21-0,34 mum and diffusion coefficient ranging from 1.6 x 10(-16) to 10(-17) m(2) s(-1). The photovoltaic parameters of the CdZnTe/CdTe heterostructrure have been determined. (C) 2002 Elsevier Science B.V. All rights reserved.