Raman studies in CdS thin films in the evolution from cubic to hexagonal phase

CdS polycrystalline thin films prepared onto glass substrates by the chemical bath deposition method at 80 degrees C showed cubic crystalline structure (beta-CdS). Upon thermal annealing in Ar + S-2 flux at different temperatures in the range 200-510 degrees C, the crystalline structure evolution of layers from the cubic modification (as-grown sample) to hexagonal phase (annealed at highest temperature samples) has been observed. At around 300 degrees C the critical point of the phase transition has been experimentally determined to occur. Raman spectroscopy measurements were carried out at room temperature for as-grown and annealed layers. The A(1)(LO) + E-1(LO) modes at 305 cm(-1) and replicas appear for as-grown and annealed samples. The E-1(TO) and the A(1)(TO) modes were also observed. A classic simple approach is proposed in order to explain the presence of the TO modes. (C) 1997 Elsevier Science Ltd.