M. García

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.

OPTICAL AND ELECTRICAL PROPERTIES OF ALUMINUM OXIDE FILMS DEPOSITED BY SPRAY PYROLYSIS

The optical and electrical characteristics of spray pyrolysis deposited aluminum oxide films are reported. The films were deposited from a spraying solution of aluminum acetylacetonate in N,N-dimethylformamide using an ultrasonic mist generator on (100) Si substrates. The addition of water mist during the spraying deposition process resulted in an overall improvement of the films characteristics. The substrate temperature during deposition was in the 450–650u2009°C range. Deposition rates up to 90 A/s were obtained depending on the spraying solution concentration and substrate temperature with an activation energy of the order of 31 kJ/mol. The optical energy band gap for these films was 5.63 eV and the refractive index at 630 nm up to 1.66 was measured by ellipsometry. The electrical characteristics of the films were determined from the capacitance and current versus voltage measurements of metal–oxide–semiconductor (MOS) structures incorporating them. A dielectric constant of 7.9, interface states density o...

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.

A study of the dielectric characteristics of aluminum oxide thin films deposited by spray pyrolysis from Al(acac)3

Abstract The dielectric characteristics of aluminum oxide thin films deposited by the spray pyrolysis technique are reported. The films were deposited with different molarities from a spraying solution of aluminum acetylacetonate and N , N -dimethylformamide. The films were deposited on silicon substrates at temperatures ranging from 450 to 650°C. The addition of water mist during the deposition process led to a remarkable improvement of the overall characteristics of the films. Films with excellent dielectric characteristics and low surface roughness were obtained. The results of the characterization indicate that there is a significant presence of carbon in the films. This carbon in the films modifies the electrical conduction characteristics leading to behavior similar to that displayed by off-stoichiometric silicon oxide (SiO 2 ) films. It is observed that the overall resistivity of the film decreases when both the molarity of the solution and the deposition temperature increase. This behavior correlates with the increase in the amount of carbon remaining inside the film. The films as deposited have a surface state density in the range of 10 11 1/eV-cm 2 and are able to stand electric fields higher than 5 MV/cm without observing dielectric breakdown.

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.

Structural and photoluminescent characteristics of yttrium–aluminum oxide films doped with Tb, Eu or Ce

Abstract The structural and room temperature luminescent characteristics of rare earth doped yttrium–aluminum oxide films deposited by the spray pyrolysis technique at low temperatures have been studied as a function of the deposition parameters such as substrate temperature and dopant concentration. The spraying solution is prepared by mixing yttrium and aluminum chlorides in water, and the incorporation of the rare earth dopants is achieved by adding chloride salts of these elements to this solution. The photoluminescent emission from Tb- and Eu-doped films have the spectral characteristics typical of radiative transitions among the electronic energy levels associated with the 3+ ionized states of these atoms. The Ce doped films, on the other hand, present a blue emission that is associated with transitions within the energy states of the CeCl 3 molecule used for the doping process of the film. The X-ray diffraction measurements of these films indicated poor crystallinity in general, with small crystalline peaks and a broad amorphous component that tend to be reduced as the deposition temperature is increased.

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.

Metal oxide Co and Co-Fe-Cr films deposited on glass substrates from a metal-organic aerosol atomised by means of ultrasonic excitations

Abstract Thin films of metal oxides of Co and the Co -Fe -Cr system were deposited on a commercial soda-lime-silica float gray glass from an aerosol generated by ultrasonic excitation, using acetylacetonates as the source of the aerosol. Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) studies performed prior to the film deposition revealed a principal difference between the thermal decomposition of acetylacetonates and the nitrates used previously, influencing greatly the properties of the synthesised films. Deposited films were characterised by the measurement of their optical properties that are vital for privacy purposes (i.e., reflectance, transmittance), and of their surface roughness and thickness measurements. Crystallinity of films has been investigated and chemical durability tests have been performed. Results of these investigations are presented and the properties of films are compared with those obtained from films deposited previously from a nitrate aerosol generated either pneumatically or by means of ultrasonic excitation.

Preliminary studies of thin metal oxide films prepared by deposition of an aerosol generated ultrasonically from aqueous nitrate solutions

Abstract Thin Co, Co-Fe and Co-Fe-Cr metal oxide films were prepared by deposition of an aerosol generated by ultrasonic excitations from aqueous nitrate solutions. Commercial gray glass has been used as substrates. Thermogravimetric (TG and DTG) measurements of initial nitrate components as well as their homogenized mixtures were performed and optical properties, i.e. reflectance and transmittance of the deposited films in the UV-visible and near-infrared regions up to 4761 nm, were measured. The surface roughness of the films was also measured and their chemical durability tested. The reflectance values obtained for 550 nm radiation wavelength were 25–33% for Co-oxide films compared to 20–30% for films deposited by us from a pneumatic aerosol, or values of 10–15% reported by others. The reflectance was 21–28% for Co:Fe = 15:1 films and up to 26% and 30% for Co:Fe:Cr = 15:1:0.25 and Co:Fe:Cr = 12:3:1 films, respectively. The reflectance of the uncoated reference glass was 5%. The surface roughness values of films deposited from ultrasonic aerosol dropped to about 50–60% of the value measured for films deposited from pneumatic aerosol. At the same time the chemical durability of films deposited from ultrasonic aerosol has approximately doubled.