A. Ortíz

Luminescent properties of ZnS:Mn films deposited by spray pyrolysis

The room temperature, photoluminescent properties of manganese‐doped zinc sulfide films deposited by spray pyrolysis are reported. These films were deposited on Pyrex glass substrates at atmospheric pressure using air as a carrier gas. All films were polycrystalline with a wurtzite (hexagonal) structure. The manganese doping was achieved by mixing MnCl3 with the starting solution to deposit ZnS. The photoluminescence spectra was measured at room temperature as a function of the different deposition parameters and the Mn concentration. Besides the characteristic light emission associated with Mn impurities in a ZnS matrix, a peak associated with the self‐activated emission was also observed under certain deposition conditions (low substrate temperatures and/or long deposition times). The presence of chlorine impurities in the films is suggested to be associated with this emission. The Mn luminescence presents a quenching effect with the Mn concentration. This quenching effect is similar to the one reported on films deposited by other techniques. The light emission at this center has an activation energy of 0.71±0.05 eV with the deposition temperature. This energy is proposed to be related with the energy required by the Mn atoms to find a proper site during the growth process to form a Mn2+ center.

Tin sulphide films deposited by plasma-enhanced chemical vapour deposition

Tin sulphide thin films have been prepared by the plasma enhanced chemical vapour deposition technique, using and as source materials. For given values of the deposition pressure, relative gas flow rates and deposition time, the plasma power density and the substrate temperature were varied in the ranges from 0.023 to 0.080 W and from 100 to 300 respectively. The deposited films show an orthorhombic crystalline structure for the entire plasma power range and for substrates temperatures higher than 150. From the studied optical properties, considering that this is an indirect energy bandgap material, the energy bandgap is calculated to have a value of 1.16 eV; the phonon involved in the electronic transition has an energy of 0.18 eV. From the measurements of electrical conductivity as a function of temperature an activation energy of 0.3 eV was determined with a p-type electrical conductivity.

Photoluminescent characteristics of lithium-doped zinc oxide films deposited by spray pyrolysis

Abstract Lithium-doped and undoped zinc oxide photoluminescent films prepared by the spray pyrolysis technique have been studied. The photoluminescent emission for the Li-doped films is formed by a broad band composed of the overlapping of four peaks at 508.590,604 and at ∼ 810 nm; undoped films present the well known blue-green emission characteristic of ZnO. The photoluminescent excitation spectra indicate that the excitation mechanism is primarily due to electron-hole pair generation across the ZnO energy bandgap, although the excitation spectra also show two smaller peaks at 508 and 524 nm, which seem to be related to an electron excitation to localized states within the bandgap. The decay time measurements of the phololuminescence show that the lifetime of the luminescence emission is of the order of 187 ns. The behavior of the luminescent intensity with temperature shows an activation energy of 0.057 eV for competitive non-radiative transitions.

Effects of precursor concentration on the optical and electrical properties of SnXSY thin films prepared by plasma-enhanced chemical vapour deposition

We have carried out the electrical and optical characterization of thin films of compounds based on Sn–S bonds (SnS2, Sn2S3), prepared by plasma-enhanced chemical vapour deposition (PECVD), as a function of the relative concentration of the precursor vapours, SnCl4 and H2S, keeping all other deposition parameters constant. In all studied cases, the deposited films were formed by polycrystalline materials. The optical bandgap values of deposited materials were calculated from optical transmittance and reflectance measurements. The SnS2 compound produced under certain deposition conditions has a forbidden bandgap around 2.2 eV. This compound shows n-type electrical conductivity, whose dark value at room temperature is 2 × 10−2 (Ω cm)−1. Also, it shows the typical semiconductor dependence of its electrical conductivity on the temperature with an activation energy of about 0.15 eV. However, thin films of a mixture of SnS2 and Sn2S3 compounds were deposited with higher values of the relative concentration of source vapours than those used to obtain the SnS2 compound. The optical bandgap shows a decreasing trend as the relative concentration increases. A similar trend is observed for dark electrical conductivity. These results create the opportunity to use SnX SY compounds in thin films for building heterojunction solar cells prepared completely by PECVD.

Spray pyrolysis deposition of thin films

Ternary compound thin films have been prepared on Pyrex glass substrates by the spray pyrolysis process using tin chloride and n, n-dimethylthiourea as starting materials. The depositions were carried out at a substrate temperature of . The identification of the phase was achieved by means of x-ray diffraction measurements. The optical reflectance and transmittance of the prepared films were used to obtain the variation of the refractive index and the extinction coefficient as a function of the wavelength. These calculated values were used to find the absorption coefficient and the optical bandgap and gave . From measurements of the conductance as a function of , a dark activation energy was determined with a value of 1.02 eV.

Lack of chemical interaction of hydrogenated amorphous silicon with indium-doped zinc oxide transparent conductive films

Abstract Indium-doped zinc oxide films have been prepared by the spray pyrolysis technique using air as a carrier gas at atmospheric pressure. These films show the excellent optical and electrical characteristics of a transparent conductive coating, with a sheet resistance of 15 Ω/square and an average optical transmission of about 88%. All the studied films show the wurtzite hexagonal crystalline structure. The results of Auger electron spectroscopy show that there was no reduction of the oxide film when an a-Si : H film was deposited by the plasma decomposition of silane at substrate temperatures in the range 150–300°C. A steep interface between the transparent conductive film and the hydrogenated amorphous silicon film was observed. Also, it was found that the depth distribution of the constituent atoms zinc, oxygen and indium in the ZnO : In film was homogeneous.

Photoluminescence characteristics of undoped and terbium chloride doped zinc oxide films deposited by spray pyrolysis

The photoluminescence characteristics of undoped and TbCl3‐doped zinc oxide films deposited by the spray pyrolysis technique are reported. Undoped films present the characteristic blue‐green emission peak at ∼508 nm observed in single‐crystal and powder ZnO. The TbCl3‐doped films present a luminescence peak at ∼540 nm. The light emission of the doped films decreases with time of exposure of the sample to the excitation light. The phenomenon is interpreted in terms of a simple model in which a competitive process of hole trapping and phototrapping occurs at a radiative recombination center generated by the TbCl3.

Photoluminescent properties of indium-doped zinc oxide films prepared by spray pyrolysis

Abstract Photoluminescence from indium-doped zinc oxide is reported on films prepared by spray pyrolysis as a function of the substrate temperature and solution flow rate. All deposited films are polycrystalline and have a hexagonal crystalline structure, but high solution flow rates result in larger disorder on the orientation of the polycrystallites. The optical absorption edge is independent of the preparation conditions. The photoluminescent spectra depend on both the substrate temperature and on the solution flow rate. Spectra from films deposited at low substrate temperature or with high solution flow rate show a broad peak centered at λ⋍530 nm which could be associated with a (InZn VZn)- luminescent center. Luminescence measurements were also carried out on films with similar thickness to rule out the effects due to variations of thickness with the different deposition conditions investigated.

Low temperature SiO2 films deposited by plasma enhanced techniques

Abstract The use of silicon halides to obtain SiO2 films with plasma enhanced chemical vapor deposition (PECVD) techniques at low temperatures is reported. The silicon halides used were SiF4 and SiCl4. SiF4 was used in a direct PECVD system while a remote-PECVD (RPECVD) system was used with SiCl4. The deposition temperature was 250°C in the first case and in the range of 25–200°C in the second case. Optical measurements such as ir%T and ellipsometry and measurements of wet etch rate were used to characterize the films. It was found that the oxides were free of OH even for oxides deposited at the lowest temperatures. The electrical properties of the oxides were measured from metal-oxide-semiconductor structures fabricated with them. Breakdown fields for these oxides were typically of the order of 8 MV cm−1 and the fixed charge density in the range of 1010–1011 charges cm−2.

Plasma enhanced chemical vapor deposition of SiO 2 films at low temperatures using SiCl 4 and O 2

Silicon dioxide films have been deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD) technique using SiCl4 and O2 as reactive materials. Infra-red transmittance, Auger electron spectroscopy analysis, ellipsometry, electrical, and chemical etch measurements have been used to characterize these films. It is possible to obtain good quality oxides at a substrate temperature of 200° C using a low flow of reactant gases. High flow of reactant gases results in highly non-homogeneous porous films. The best oxide films obtained show destructive breakdown at electrical fields above 4 MV/cm and a fixed charge density of the order of 2.6 × 1011 charges/cm2.