Search

Structural, morphological and optical properties of CdS films, deposited by the pulsed laser ablation technique on SnO2:F/glass substrates, were studied as a function of time deposition. Up to our knowledge the properties of these films grown onto conducting polycrystalline substrates have not been reported before. The photoluminescence measurements showed the existence of an exciton peak at room temperature, as an indication of good crystalline quality of the layers. A thermal treatment was applied to the samples in a 100 mT Ar atmosphere at 400 °C for 30 min after the deposition of a CdCl2 layer on them. Films characterization was carried out through X-ray diffraction, photoluminescence and atomic force microscopy measurements. The structural, optical and morphological properties as a function of growth parameters are presented and discussed. Thermal treatment makes uniform the grain size in the samples, with a tendency to increase the grain size average. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper, we present a comparative study of photoluminescence and its relation to the structural properties of cadmium sulphide (CdS) thin films grown by chemical bath deposition (CBD), close spaced vapour transport, laser ablation (LA) and sputtering. Taking into account that the physical properties of CdS thin films depend upon the growth technique and the optimization of the deposition conditions for each technique, we show that the best crystal perfection occurs for LA-CdS films since the main photoluminescence peak at low temperature is due to bound excitons (2.53 eV). As expected, the films with the worst crystalline quality are those grown by CBD, ascertained by the photoluminescence band around 1.72 eV due to sulfur vacancies ('red band') without the corresponding exciton band. The photoluminescence results are correlated to x-ray diffraction measurements that confirm the above results.

CdS polycrystalline thin films prepared onto glass substrates by the chemical bath deposition method at 80°C showed cubic crystalline structure (β-CdS). Upon thermal annealing in Ar + S2 flux at different temperatures in the range 200–510°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°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 A1(LO) + E1(LO) modes at 305 cm−1 and replicas appear for as-grown and annealed samples. The E1(TO) and the A1(TO) modes were also observed. A classic simple approach is proposed in order to explain the presence of the TO modes.

A calculation is presented on the evolution of longitudinal and transverse optical phonons as a function of the concentration parameter x in the system ZnxCd1−xSe. The calculation is based in an isodisplacement model of the atoms which include interactions to first and second neighbors. The model is fitted to Raman measurements carried out on thin-film samples grown by Close Spaced Vapor Transport (CSVT). Comparison to the experimental data allows to conclude that the x-dependence of these optical modes corresponds to an intermediate-mode behavior.

Raman scattering (RS) is a very important experimental tool to characterize the optical modes and another elementary excitations of materials. Among other issues it can determine for example the degree of crystalline quality and point defects like local modes. Therefore GaN - thin films and related compounds for photovoltaic purposes and as processed by several systems have been measured by this technique. The films were grown by Molecular Beam Epitaxy (MBE), Close Spaced Vapor Transport (CSVT) and Laser Ablation (LA) with the use of optimal growth parameters and substrates. Gallium nitride crystallizes in the wurtzite structure with 4 atoms in the unit cell and presents 7 allowed Raman modes of A 1 , E 1 , and E 2 symmetries. In this work we present and discussed our Raman experiments where particularly the detection of the E 2 and A 1 modes are illustrated in these nitride semiconductor compounds.

In this paper, a comparative study of the properties of CdS thin films grown by laser ablation (LA), close space vapour transport (CSVT), sputtering (Sp) and chemical bath deposition (CBD) is presented, taking into account that the physical properties of CdS thin films depend upon the growth technique, and the optimisation of the growth conditions for each technique. We summarize and discuss our results on growth kinetics, electrical, optical, structural and morphological characteristics, in order to have a more complete evaluation of those techniques for making CdS thin films to be applied to solar cells.