4Instituto de Investigaciones en Materiales, UNAM, México, D.F.

Thin films of II-VI semiconducting materials like cadmium seleide have been currently studied because its important application in solar cells fabrication. This compoind material has been grown by means of several deposition techniques: MBE, sputtering, laser ablation, chemical bath, among others. The layers can be grown either in the cubic zincblende modification or in the hexagonal stable structural phase wurtzite. We have grown CdSe thin films in cubic and hexagonal phases on glass substrates by means of the chemical bath method, at 65ºC and with a 200 nm thickness. X-ray diffraction analysis allow to determine the crystalline structure of samples. By calculating the second derivative of the optical absorption spectra two electronic transitions were evidenced. The fundamental at 1.8 eV and a second one at 2.2 eV. Stoichiometric analysis allowed to observe either an excess of cadmium or an excess of selenium, depending on the chemical grown conditions. Cd-enriqued films show a type-n conductivity an Se-enriched films a type p conductivity. This property can be useful for photovoltaic applications.