In this letter we report on cubic CdS thin films with low resistivity by chemical bath deposition (CBD) technique and subsequent annealings in S2 and H2+In. Low temperature photoluminescence, x rays, and transmission spectra support the assumption that S2 annealings contribute to fill the vacancies in the as-deposited films leading to an enlargement of the CdS cubic cell. This fact is revealed by an increase in interplanar distances, evanescence of the PL red broad band, and decrease in band-gap energies. Cubic phase remains after H2+In annealing at higher temperatures. A resistivity as low as 11 Ω cm was obtained at an optimum annealing temperature of 350 °C.

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Chemically -driven isothermal close space vapour transport was used to prepare pure MoO2 films which were eventually converted to MoO3 by annealing in air. According to temperaturedependent Raman measurements, the MoO2/MoO3 phase transformation was found to occur in the 225 -350 o C range; no other phases were detected during the transition. A clear change in composition and Raman spectra, as well as noticeable modifications of the band gap and the absorption coefficient confirmed the conversion from MoO2 to MoO3. An extensive characterization of films of both pure phases was carried out. In particular, a procedure was developed to determine the dispersion relation of the refractive index of MoO2 from the shift of the interference fringes the used SiO2/Si substrate. The obtained refractive index was corrected taking into account the porosity calculated from elastic backscattering spectrometry. The Debye temperature and the residual resistivity were extracted from the electrical resistivity temperature dependence using the Bloch -Grüneisen equation. MoO3 converted samples presented very high resistivity and a typical semiconducting behaviour. They also showed intense and broad luminescence spectra, which were deconvoluted considering several contributions; and its behaviour with temperature was examined. Furthermore, surface photovoltage spectra were taken and the relation of these spectra with the photoluminescence is discussed.

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A detailed reflection high-energy electron diffraction analysis shows relevant features of the lattice parameter relaxation of CdSe thin films grown in a layer-by-layer mode onto ZnSe. In situ investigations of different azimuths show a clear lattice parameter oscillation in the ͓110͔ azimuth. The lattice parameter has a minimum value ͑similar to that of ZnSe͒ during Se exposure steps, and a higher and increasing lattice parameter during Cd exposure steps. The behavior is ascribed to the formation of CdSe islands during Cd exposure steps. The cumulative effect in CdSe exposure steps is considered to be a consequence of a decrease in the island size with the number of cycles. Actual plastic deformation does occur after 5 ML.Lattice relaxation in strained thin film semiconductors has became a very important point recently. Following the standard accepted criterion, it can be considered that the strained overlayer suffers a tetragonal distortion with the inplane lattice parameter being equal to that of the substrate and the transverse lattice parameter being reduced ͑enlarged͒ for in-plane tensile ͑compressive͒ strain, according to the elasticity theory. This pseudomorphic growth continues until the stress is relaxed through misfit dislocation formation or ͑for largely mismatched systems͒ three-dimensional ͑3D͒ island formation. However, evidence has been reported of a much more complicated relaxation process 1 in which the lattice parameter has been observed to oscillate during molecular beam epitaxy ͑MBE͒ growth of In x Ga 1Ϫx As onto GaAs substrates. The effect has been also observed in some metallic thin films 2,3 and in the II-VI semiconductor ZnTe grown onto CdTe, 4 always using the MBE technique. It has been ascribed to the relaxation of the strain in the edges of the growing islands. A strong anisotropy in the relaxation process has been noticed concurrently with the oscillation of the lattice parameter. 3,4 The geometry of the islands or the stress induced by surface contamination or reconstruction has been invoked to explain this anisotropy. Anisotropic lattice parameter oscillations have been also observed in metallic and semiconducting 5 homoepitaxial structures. In this last reference both MBE and atomic layer epitaxy ͑ALE͒ were used for growing CdTe homoepitaxial films.In this letter we report the occurrence of lattice parameter oscillations in the CdSe/ZnSe system. To explore this highly strained system we used ALE instead of MBE used in the earlier studies of heteroepitaxial films. In our growth conditions, the ALE regime was observed ͑it was verified in previous CdSe growth experiments͒ to be self-regulated at 0.5 ML per cycle. For this, we could separate the influence of the roughness induced by fractional surface coverages and that due to the different morphologies of Cd and Se terminated surfaces, as will be explained later.The CdSe/ZnSe structures were grown in a RIBER 32P MBE system onto semi-insulating GaAs ͑001͒ substrates at 260°C. As received episubstrates were introduced in the MBE chamber...

Photoluminescence (PL) studies in GaN thin films grown by infrared close space vapor transport (CSVT-IR) in vacuum are presented in this work. The growth of GaN thin films was done on a variety of substrates like silicon, sapphire and fused silica. Room temperature PL spectra of all the GaN films show near band-edge emission (NBE) and a broad blue and green luminescence (BL, GL), which can be seen with the naked eye in a bright room. The sample grown by infrared CSVT on the silicon substrate shows several emission peaks from 2.4 to 3.22 eV with a pronounced red shift with respect to the band gap energy. The sample grown on sapphire shows strong and broad ultraviolet emission peaks (UVL) centered at 3.19 eV and it exhibits a red shift of NBE. The PL spectrum of GaN films deposited on fused silica exhibited a unique and strong blue-green emission peak centered at 2.38 eV. The presence of yellow and green luminescence in all samples is related to native defects in the structure such as dislocations in GaN and/or the presence of amorphous phases. We analyze the material quality that can be obtained by CSVT-IR in vacuum, which is a high yield technique with simple equipment set-up, in terms of the PL results obtained in each case.