J. G. Quiñones-Galván

Physical properties of CdTe:Cu films grown at low temperature by pulsed laser deposition

CdTe:Cu films were grown by pulsed laser deposition on Corning glass slides at a substrate temperature of 300 °C. The thin films were grown using CdTe and Cu2Te powders, varying the Cu2Te concentration from 3 to 10 wt. %. The structural, compositional, optical, and electrical properties were analyzed as a function of the nominal copper concentration. X-ray diffraction shows that films have CdTe cubic phase. The compositional analysis indicates that CdTe:Cu films grown with lower Cu content have Te excess, on the other hand, films with higher Cu content have Te deficiencies. The electrical measurements showed that CdTe:Cu films grown with low Cu content present lowest resistivity.

Structural and optical properties of Cu-doped CdTe films with hexagonal phase grown by pulsed laser deposition

Cu-doped CdTethin films were prepared by pulsed laser deposition on Corning glass substrates using powders as target. Films were deposited at substrate temperatures ranging from 100 to 300 °C. The X-ray diffraction shows that both the Cu-doping and the increase in the substrate temperature promote the presence of the hexagonal CdTe phase. For a substrate temperature of 300 °C a CdTe:Cu film with hexagonal phase was obtained. Raman and EDS analysis indicate that the films grew with an excess of Te, which indicates that CdTe:Cu films have p-type conductivity.

Synthesis of visible light emitting self assembled Ge nanocrystals embedded within a SiO2 matrix

As-grown light emitting self-assembled Ge nanocrystals (Ge-NCs) embedded in a SiO2 matrix were produced via a sequential deposition process of SiO2/Ge/SiO2 layers employing a reactive radio frequency sputtering technique. Obtained Ge-NCs show a crystallographic phase, the proportion, size, quality, and specific orientation of which are determined by the oxygen partial pressure. Photoluminescence (PL) spectra indicate that the size distribution of Ge-NCs is reduced and centered on about 8 nm when higher oxygen partial pressure is employed; the formation of Ge-NCs is corroborated by transmission electron microscopy measurements, and their sizes are consistent with estimates from PL measurements. Resistivity measurements are explained by a near neighbors hopping process, with specific features depending on the Ge-NCs’ size. The features of PL and resistivity measurements indicate that there is no appreciable dependence of the number of interfacial defects on the oxygen partial pressure.

Influence of plasma parameters and substrate temperature on the structural and optical properties of CdTe thin films deposited on glass by laser ablation

In the pulsed laser deposition of thin films, plasma parameters such as energy and density of ions play an important role in the properties of materials. In the present work, cadmium telluride thin films were obtained by laser ablation of a stoichiometric CdTe target in vacuum, using two different values for: substrate temperature (RT and 200 °C) and plasma energy (120 and 200 eV). Structural characterization revealed that the crystalline phase can be changed by controlling both plasma energy and substrate temperature; which affects the corresponding band gap energy. All the thin films showed smooth surfaces and a Te rich composition.

Study of the structure, optical properties, surface morphology and topology of ZnO thin films grown by sol–gel on silicon substrates

Polycrystalline visible light photoluminescent zinc oxide (ZnO) thin films have been grown on silicon substrates by the dip immersion sol?gel technique at low sintering temperature. The optical properties of the films were analyzed by UV?vis spectroscopy. The structural properties were measured with x-ray diffraction. The results show that the films are polycrystalline and have hexagonal wurtzite structure. The estimated band gap of the samples by UV?vis absorption spectroscopy is in good agreement with the value measured by UV?vis reflectance spectroscopy and is near 3.2 eV. The surface topography was observed with atomic force microscopy. The morphology of the samples was analyzed by scanning electron microscopy. Energy dispersive x-ray spectroscopy was used to make chemical composition measurements, the results indicate that the sample is stoichiometric. The photoluminescence (PL) spectroscopy shows a strong band in the blue?green region of the spectrum, which makes these films interesting to optoelectronic applications.

Stoichiometric 6H-SiC thin films deposited at low substrate temperature by laser ablation

Silicon carbide thin films were grown by laser ablation on silicon substrates at different deposition temperatures using SiC powders as target material. The structural, morphological, compositional, and optical properties were studied as a function of the deposition temperature. The 6H-SiC crystalline phase was observed by Raman spectroscopy, x-ray diffraction, and transmission electron diffraction without the presence of any other polytype. In the room temperature photoluminescence spectra, a broad band was observed in the visible region which suggests that these films can have applications on silicon based optoelectronics.

Synthesis of Light Emitting Ge Nanocrystals by Reactive RF Sputtering

In this work we report the results of the synthesis, structural and optical characterization of SiO2/Ge/SiO2 heterostructures by reactive RF sputtering. The SiO2 films were grown by reactive sputtering employing a plasma mixture of oxygen and argon. The Ge layer was grown employing an Ar atmosphere. The samples were prepared on p-type Si (1 1 1) substrates by reactive sputtering. The effect of the partial pressure of oxygen on the electronic properties of the heterostructure is reported[1]. Structural characterization was carried out by grazing angle X-ray difraction. Surface roughness was quantified by atomic force microscopy. The presence of Ge nanocrystals (Ge-NCs) was evidenced by X-ray diffraction. The vibrational properties were studied by Raman spectroscopy. The Raman spectra showed modes associated to germanium indicating the formation of low dimensionality germanium particles embedded within a SiO2 matrix. Photoluminescence emission is observed around ~1.7 eV and it is associated to the quantum confinement of carriers in Ge-NCs. Ohmic contacts were deposited using a van der Pauw geometry employing an a AuSb alloy for the contacts. Temperature dependent Hall (T-Hall) measurements were done between 35 K and 150 K, using the van der Pauw method. The results indicated low resistivity values that could be explained due to some variable range hopping conduction mechanism.

Structural properties of Sn-doped CdTe thin films grown by pulsed laser deposition using powder as target

Undoped and Sn-doped CdTe thin films were grown by a pulsed laser deposition on glass substrates at 300 °C using a powder as target. CdTe films were grown using CdTe and Sn powders, varying the tin concentration in the range of 1–7 wt. %. The structural properties were analyzed as a function of the Sn amount in the target. The x-ray diffraction shows that the undoped CdTe film has a cubic phase, while Sn-doped CdTe films have a mixture of cubic and hexagonal phases. The compositional analysis showed that the undoped CdTe film has Te excess, while Sn-doped CdTe films have Te deficiencies.

Temperature dependent transport study of the SiOx/Ge/SiOx system

The transport properties of the SiOx/Ge/SiOx system are studied using the van der Pauw technique as function of temperature in the range from 35 K to 150 K for two representative samples grown by Radio Frequency sputtering under different conditions. It is found that variable range hopping conduction explains the temperature dependence of the resistivity. For both samples, the nearest neighbor hopping conduction process explains the temperature dependence of the resistivity in the range between 66 K and 150 K. For the sample with the roughest surface, Efros-Shkovskiis variable range hopping process explains better the results below 66 K, while for the other one, a combination of Motts variable range hopping in two and three dimensions explain better the results in the same temperature range.