Semiconducting CdSe films have been continuously studied as a photoconductive material 1,2 for their importance in photovoltaic energy conversion, 3,4 and lately, for their noticeable quantum confinement effect properties. [5][6][7][8] Wurtzite is the stable phase of CdSe, and the sphalerite CdSe modification is a metastable structural phase. In spite of the relatively abundant works published in CdSe thin films, this material is the least studied II-VI compound in thin-film format, especially for cubic CdSe. Many physical properties of cubic CdSe remain as unconcluded studies, for instance, band structure and phonon dispersion, among others. By using new deposition techniques like molecular beam epitaxy, 9 laser ablation, 10 electrochemical atomic layer, 11 etc., it has been possible to grow CdSe in cubic phase with a wide variety of changing growth conditions. In this way, a lot of information has been gained recently for a better understanding of the physical properties of thin films of this material.In this work the chemical bath deposition (CBD) technique was used to prepare polycrystalline CdSe thin films on glass substrates having about 200 nm thickness. Although this technique has been already used to grow this material, 1,2,12 the optical and electrical properties usually depend upon the growing parameters such as temperature, stirring, chemical agents, and concentrations during the grown process. Thus, stoichiometric thin films of CdSe in cubic phase were obtained similar to CdS with the same structural symmetry using the CBD technique. 13 Band structure analysis from optical absorption data evidenced two critical points at 1.84 and 2.2 eV, respectively. Theoretical calculations of band structure of cubic modification of CdSe do not predict the existence of this last electronic transition; 14,15 however, the recent experimental data of dielectric function in cubic CdSe reveal a spin-orbit split of 0.41 eV in accordance with our results. 16 Dark conductivity (DC) measurements in the 100-500 K range showed the presence of a high density of deep levels that promotes the carrier conduction described by the Mott's variable range hopping (VRH) model. After this first round of DC measurements, two consecutive rounds, in the same range of temperature, were carried out. Then the high density of deep levels disappeared and the conductivity was dominated by a thermally activated process following Arrhenius behavior. The crystalline quality of the films improved already after the first cycle of measurements, as this acted like a thermal annealing.
