Systematic studies have been undertaken to investigate the effect of Tl doping on thin film properties of chemically deposited CdSe. Thin films of CdSe and doped CdSe with Tl ions were obtained by a chemical deposition technique in alkaline medium at 60degreesC. The films were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), optical absorption, electrical conductivity and thermoelectric techniques. The studies revealed that pure and Tl doped CdSe films are polycrystalline in cubic structure. A decrease in electrical resistivity and optical bandgap are observed as Tl3+ doping concentration increases to 0.07 mol%. The optical transition is found to be of direct "allowed" type. The thermoelectric power measurements showed n type conduction mechanism for all doped samples. It is proposed that Tl3+ dissolves substitutionally in CdSe lattice in lower concentration range. (C) 2002 Published by Elsevier Science B.V.