J. Carrillo-López

Photoconduction in silicon rich oxide films obtained by low pressure chemical vapor deposition

Photoconduction properties of silicon rich oxide (SRO) thin films were studied under different illumination conditions. In the past, Al/SRO/Si structures showed a high photocurrent in spite of the fact that an opaque Al layer was on the active area. In order to elucidate this observation, new Al/SRO/Si structures were tested, but this time they were also measured horizontally. SRO thin films were deposited on silicon wafers by low pressure chemical vapor deposition technique using SiH4 (silane) and N2O (nitrous oxide) as reactive gases at 700°C. 1%–12% silicon excess was used. Structures with a single SRO layer and with a double layer were fabricated in order to have a barrier to isolate the silicon from the active SRO layer. The results show that all structures have a higher current when light shines on them than when they are in the dark. It is proposed that the photocurrent is produced in the SRO bulk, and an explanation for these observations is given.

Compositional and optical properties of SiO x films and (SiO x /SiO y ) junctions deposited by HFCVD

In this work, non-stoichiometric silicon oxide (SiOx) films and (SiOx/SiOy) junctions, as-grown and after further annealing, are characterized by different techniques. The SiOx films and (SiOx/SiOy) junctions are obtained by hot filament chemical vapor deposition technique in the range of temperatures from 900°C to 1,150°C. Transmittance spectra of the SiOx films showed a wavelength shift of the absorption edge thus indicating an increase in the optical energy band gap, when the growth temperature decreases; a similar behavior is observed in the (SiOx/SiOy) structures, which in turn indicates a decrease in the Si excess, as Fourier transform infrared spectroscopy (FTIR) reveals, so that, the film and junction composition changes with the growth temperature. The analysis of the photoluminescence (PL) results using the quantum confinement model suggests the presence of silicon nanocrystal (Si-nc) embedded in a SiOx matrix. For the case of the as-grown SiOx films, the absorption and emission properties are correlated with quantum effects in Si-nc and defects. For the case of the as-grown (SiOx/SiOy) junctions, only the emission mechanism related to some kinds of defects was considered, but silicon nanocrystal embedded in a SiOx matrix is present. After thermal annealing, a phase separation into Si and SiO2 occurs, as the FTIR spectra illustrates, which has repercussions in the absorption and emission properties of the films and junctions, as shown by the change in the A and B band positions on the PL spectra. These results lead to good possibilities for proposed novel applications in optoelectronic devices.PACS61.05.-a; 68.37.Og; 61.05.cp; 78.55.-m; 68.37.Ps; 81.15.Gh

UV-Vis Photodetector with Silicon Nanoparticles

J.A. Luna-Lopez1, M. Aceves-Mijares2, J. Carrillo-Lopez1, A. Morales-Sanchez3, F. Flores-Gracia1 and D.E. Vazquez Valerdi1 1Science Institute-Research Center for Semiconductor Devices-Autonomous Benemerita University of Puebla 2Department of Electronics, National Institute of Astrophysics, Optics and Electronics INAOE 3Centro de Investigacion en Materiales Avanzados S. C., Unidad Monterrey-PIIT, Apodaca, Nuevo Leon, Mexico

Structural and Morphological Properties of Nanostructured ZnO Particles Grown by Ultrasonic Spray Pyrolysis Method with Horizontal Furnace

ZnO nanoparticles were synthesized in a horizontal furnace at 500°C using different zinc nitrate hexahydrate concentrations (0.01 and 0.1 M) as reactive solution by ultrasonic spray pyrolysis method. The physical-chemical properties of synthesized ZnO nanoparticles have been characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and high resolution transmission electron microscopy (HRTEM). With the TGA is has optimized the temperature at which the initial reactive (Zn(NO3)2·6H2O), is decomposed completely to give way to its corresponding oxide, ZnO. SEM revealed secondary particles with a quasispherical shape that do not change significantly with the increasing of precursor solution concentration as well as some content of the broken spheres. Increasing the precursor solution concentration leads to the increase in the average size of ZnO secondary particles from to nm; XRD reveals the similar tendency for the crystallite size which changes from to nm. HRTEM implies that the secondary particles are with hierarchical structure composed of primary nanosized subunits. These results showed that the precursor concentration plays an important role in the evolution on the size, stoichiometry, and morphology of ZnO nanoparticles.

Si Nanocrystals Deposited by HFCVD

The structural and optical properties of Si nanocrystal (Si-nc) embedded in a matrix of off-stoichiometric silicon oxide (SiOx, x<2) films prepared by hot filament chemical vapor deposition technique were studied. The films emit a wide photoluminescent spectra and the maximum peak emission shows a blue-shift as the substrate temperature (Ts) decreases. Also, a wavelength-shift of the absorption edge in transmittance spectra is observed, indicating an increase in the energy band gap. The Si-nc’s size decreased from 6.5 to 2.5 nm as Ts was reduced from 1150 to 900 °C, as measured through High Resolution Transmission Electron Microscopy analysis. A combination of mechanisms is proposed to explain the photoluminescence in the SiOx films, which involve SiOx defects and quantum confinement effects.

Photoconduction in silicon rich oxide films

Photoconduction of silicon rich oxide (SRO) thin films were studied by current-voltage (I-V) measurements, where ultraviolet (UV) and white (Vis) light illumination were applied. SRO thin films were deposited by low pressure chemical vapour deposition (LPCVD) technique, using SiH4 (silane) and N2O (nitrous oxide) as reactive gases at 700 °. The gas flow ratio, Ro = [N2O]/[SiH4] was used to control the silicon excess. The thickness and refractive index of the SRO films were 72.0 nm, 75.5 nm, 59.1 nm, 73.4 nm and 1.7, 1.5, 1.46, 1.45, corresponding to Ro = 10, 20, 30 and 50, respectively. These results were obtained by null ellipsometry. Si nanoparticles (Si-nps) and defects within SRO films permit to obtain interesting photoelectric properties as a high photocurrent and photoconduction. These effects strongly depend on the silicon excess, thickness and structure type. Two different structures (Al/SRO/Si and Al/SRO/SRO/Si metal-oxide-semiconductor (MOS)-like structures) were fabricated and used as devices. The photocurrent in these structures is dominated by the generation of carriers due to the incident photon energies (~3.0-1.6 eV and 5 eV). These structures showed large photoconductive response at room temperature. Therefore, these structures have potential applications in optoelectronics devices.