Comparative optical and structural studies of CdSe films grown by chemical bath deposition and pulsed laser deposition

Cadmium selenide thin films were prepared by chemical bath deposition (CBD) and pulsed laser deposition (PLD) methods. For CBD films, cadmium chloride (CdCl2) and cadmium acetate (Cd(CH3COO)2) solutions were employed as Cd2+ source while a freshly prepared sodium selenosulfite (Na2SeSO3) solution provided the Se2− ions. The pH of the bath was adjusted by adding ammonium hydroxide. The effects of the bath temperatures (30–90 °C) and the Cd/Se ratio on film properties were investigated. On the other hand, PLD films were grown by the ablation of a sintered pure CdSe target using a Nd:YAG laser beam (355 nm) with 1 J/cm2 fluence. The deposition chamber was maintained under vacuum pressure (10−6 mbar) and at room temperature. The CBD films are constituted by crystallites of metastable cubic phase (7 nm) with some amorphous phase present, whereas the PLD films showed better crystalline quality and higher crystalline size. Optical absorption analysis shows that the band gap value of the CBD films is higher than that of the bulk material and decreases with the bath temperature. Annealing transforms the metastable cubic phase into the hexagonal phase and causes a “redshift” in the band gap of the CBD and PLD films due to the crystal size increase.