Papers by Author: G.S. Contreras-Puente

Abstract: We present in this work some results concerning the effects of the thermal annealing with CdCl₂ on the optical properties of CdS thin films grown by radio-frequency planar magnetron sputtering technique, under optimized growth parameters: gas pressure, atmosphere, substrate temperature, power of plasma, etc. An improvement of the optical properties has been observed, mainly the presence of radiative emission (luminescence) at room temperature. This fact allowed us to carry out a deep study of the photoluminescence (PL) properties of the CdS films, in the range of temperature 10≤ T ≤ 300 K. Radiative emission at the high energy side has been observed and related to exitonic processes. Temperature quenching experiments gave rise to the calculation of the activation energies for each one of the radiative emissions (PL bands).

Abstract: Cadmium Selenide (CdSe) thin films were prepared by pulsed laser deposition using a Nd:YAG laser (355 nm). Films were grown by ablating a sintered pure CdSe target with fluences from 0.1 to 1.5 J/cm² on corning glass, silicon (100) and quartz substrates. Deposition chamber was maintained under vacuum pressure while substrate temperature was increased from room temperature to 500°C in order to control the crystalline phase. All the films show mirror-like surface morphology. Atomic force microscopy (AFM) images shown that films have very flat surfaces with RMS values around 0.7 and 5 nm for room temperature and 500°C respectively. The X-ray diffraction analysis proves the presence of the cubic zinc blend phase for the CdSe films deposited at low temperature, at 400°C and at higher substrate temperature the hexagonal phase is present. TEM analysis shows that at 100°C the films are constituted by particles with an average size of 30nm in diameter. The optical properties of the films were determined from the UV-transmission spectra. The estimated band gap values of the films deposited at room temperature and at 400°C (0.1 J/cm²) were 1.87 and 1.70 eV respectively.

Abstract: We present in this work experimental results and their analysis concerning the structural and optical characterization of cadmium selenide (CdSe) films grown by the Chemical Bath Deposition (CBD) technique, at different bath temperatures T_d : 0≤T_d≤80 °C. Structural characterization was carried out by using X-ray diffraction, whereas optical characterization was done by using optical absorption and photoluminescence spectroscopies. X-ray results showed a change of the crystalline structure as a function of T_d , from the zincblende to wurzite one when T_d increases from 0 to 80 °C. The respective band-gap, E_{g ,} was calculated from the absorption spectrum giving rise to values in the range 1.85 to 2.30 eV, as a function also of T_d . Thses values are higher than the well accepted value of 1.75 eV for the CdSe bulk material. The radiative emission was analyzed throughout the photoluminescence (PL) spectra. All samples showed radiative emission above the band-gap, at room temperature, this radiative emission having a dependence on the pressure inside the cryostat. A quenching of the PL signal is observed when the pressure is decreased at values as low as 60 mTorr.

Abstract: Bi-Pb-Sr-Ca-Cu-O films were deposited at 270-420°C by organic chemical spray pyrolysis deposition with triphenyl bismuth (TPB), Pb(tmhd)2, Sr(tmhd)2, Ca(tmhd)2 and Cu(tmhd)2 (tmhd: 2,2,6,6-tetramethyl-3,5-heptanedione). A factorial experimental design was applied in order to study the interaction between composition, deposition temperature, annealing time and annealing temperature and the effect in the formation of crystalline phases. Results of their structural and chemical characterization are presented.