R. Lozada-Morales

CdTeOx to CdTeO3 structural phase transition in as-grown polycrystalline films by reactive sputtering

Polycrystalline thin films of CdTeOx (x<3) and CdTeO3 were grown at 400 °C by rf-reactive sputtering. The CdTe oxide films were elaborated in an Ar–O2 atmosphere using different oxygen flow rates in the 5–11 SCCM (SCCM denotes cubic centimeter per minute at STP) range. The structural properties of the samples were studied by x-ray diffraction and micro-Raman spectroscopy. The diffraction patterns show that the films grown with oxygen flows between 5 and 10.5 SCCM present a crystalline structure similar to that of pure CdTe films, that is, a mixture of cubic zinc-blende-type and hexagonal wurtzite-type structures. However, the diffraction patterns of samples grown under an oxygen flow rate of 11 SCCM are strikingly different and in agreement with that of cubic CdTeO3, indicating that a structural phase transition was achieved. These results are in accordance with those obtained by micro-Raman spectroscopy, where the spectra of the CdTeOx samples grown with oxygen flows below 11 SCCM show an intense LO CdTe...

Spectroscopic Studies of the Behavior of Eu3+on the Luminescence of Cadmium Tellurite Glasses

The effect of europium doping on the photoluminescence of ZnO-CdO-TeO2 glasses is analyzed. TeO2-based glasses are of high interest as hosts for laser glasses. The Eu-doped oxide glasses were prepared by the conventional melt-quenching method. Five different concentrations of europium nitrate hexahydrate that varied from 0.3 to 1.5 mol% were used. SEM observations revealed the formation of zinc aluminate spinel and disperse droplets of liquid-liquid phase separation in the glasses. X-Ray diffraction reveals the amorphous structure of the fabricated glasses. FT-IR and Raman spectra show the presence of TeO4 and TeO3

Pulsed laser deposition of zinc vanadates from a ZnV2O6 target

Zinc vanadate thin films, which have the property of band gap tunability together with interesting optical and electrical properties, are excellent candidates for optoelectronic applications such as solar cells. But so far, no reports on thin films deposition of zinc vanadates exist in literature. In the present work, zinc vanadate compounds were grown on glass substrates at room temperature by pulsed laser deposition. A polycrystalline ZnV2O6 target synthesized by melt quenching was used for the ablation process. The physical properties of the films were analyzed as a function of density and the mean kinetic energy of ions in the plasma. As-deposited films were amorphous, and after annealing at 500 °C in air, the crystalline structure of the samples changed depending on the plasma density. Raman spectroscopy measurements showed the presence of several vibrational modes in different regions of the annealed samples, indicating the presence of different crystalline phases. The band gap values were 2.77 and ...

Incorporation of Er{sup 3+} ions into an amorphous matrix of Cd{sub 2}V{sub 2}O{sub 7} containing crystalline CdO nanoparticles

Er{sup 3+} ions have been introduced into a matrix of Cd{sub 2}V{sub 2}O{sub 7} using a conventional melt-quenching method. X-ray diffraction results indicate that a material constituted of CdO nanocrystals of ∼40 nm embedded within the amorphous Cd{sub 2}V{sub 2}O{sub 7} matrix was fabricated. The presence of such nanocrystals was confirmed by transmission electron microscopy. Raman spectroscopy measurements confirm that the amorphous matrix is composed by Cd{sub 2}V{sub 2}O{sub 7}. The band gap obtained by optical absorption is 2.84 eV. From the photoluminescence spectrum the electronic transitions such as ({sup 2}H{sub 11/2}, {sup 4}S{sub 3/2}, {sup 4}F{sub 9/2}, {sup 4}I{sub 9/2}) → {sup 4}I{sub 15/2} and {sup 4}S{sub 3/2} → {sup 4}I{sub 13/2} corresponding to Er{sup 3+} were observed. Thermally activated transport was observed by dark conductivity measurements taken from room temperature to 450 K. The morphology and chemical composition of the sample were determined by scanning electron microscopy and energy dispersive spectroscopy, respectively.

Temperature Dependent Charge Transport Properties Of P‐type Cux(CdTe)yOz Films Studied By Au Ohmic And Schottky Contacts

Temperature dependent current voltage measurements were done on five samples of Cux(CdTe)yOz grown by reactive rf cosputtering. The stoichiometry of the samples were different and in the high copper and oxygen concentrations regime. An Al and a Au contact were used. The Al contact was always ohmic. Depending on the composition, the Au contact yielded either a Schottky or an ohmic behavior. In the case of an ohmic behavior, one sample yielded temperature independent results, while another temperature dependent parameters. In the case of Schottky behavior, the Cheung method was used to obtain the internal resistance and the ideality factor. The current voltage behavior is well explained by tunneling, and three activation energies of 62, 89 and 186 meV are obtained for each sample. Finally, a negative differential resistance effect is found in one sample, the only one where it was possible to detect CuO and Cu2O nanoclusters using the X‐ray diffraction technique.