Rodrigo Martins

Aluminum-doped zinc oxide (AZO) transparent conductor coating has emerged as promising substitute to tin-doped indium oxide (ITO) as electrode in optoelectronic applications such as photovoltaics or light emitting diodes (LEDs). Besides its high transmission in the visible spectral region and low resistivity, AZO presents a main advantage over other candidates such as graphene, carbon nanotubes or silver nanowires; it can be deposited using the technology industrially implemented to manufacture ITO layers, the magnetron sputtering (MS). This is a productive, reliable and green manufacturing technique. But to guarantee the robustness, reproducibility and reliability of the process there are still some issues to be addressed, such as the effect and control of the target state. In this paper a thorough study of the influence of the target erosion grade in developed coatings has been performed. AZO films have been deposited from a ceramic target by RF MS. Structure, optical transmittance and electrical properties of the produced coatings have been analyzed as function of the target erosion grade. No noticeable differences have been found neither in optoelectronic properties nor in the structure of the coatings, indicating that the RF MS is a stable and consistent process through the whole life of the target. © 2016 Elsevier B.V.

Amorphous silicon carbide films were obtained by plasma enhanced chemical vapor deposition (PECVD) technique using a gas mixture of silane, methane, and hydrogen with a high excitation frequency and a high hydrogen dilution ratio. The high temperature annealing behavior of the amorphous silicon carbide films was studied by annealing at 1373 K for 1 h in nitrogen atmosphere. A very thin Au film was deposited on part of the films to investigate the metal induced crystallization effect. Well aligned nanotubes were found on the silicon carbide films covered by a thin gold layer after the high temperature annealing by atomic force microscopy. Further study is necessary to identify the nature of the nanotubes and elucidate their growth mechanism. © 2006 Elsevier B.V. All rights reserved.

Diphasic silicon films (nc-Si/a-Si:H) have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the nc-Si/a-Si:H has higher photoconductivity (σph), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. The blue shift for the stretching mode and red shift for the wagging mode in the IR spectra also show the variation of the microstructure. By using this kind of film as intrinsic layer, a p-i-n junction solar cell was prepared with the initial efficiency of 8.51% and a stabilized efficiency of 8.01% (AM1.5, 100 mw/cm2) at room temperature. © 2006.

A series of amorphous silicon carbide films were prepared by plasma enhanced chemical vapor deposition technique on (100) silicon wafers by using methane, silane, and hydrogen as reactive resources. A very thin (around 15 Å) gold film was evaporated on the half area of the a-SiC:H films to investigate the metal induced crystallization effect. Then the a-SiC:H films were annealed at 1100°C for 1 hour in the nitrogen atmosphere. Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to analyze the microstructure, composition and surface morphology of the films. The influences of the high temperature annealing on the microstructure of a-SiC:H film and the metal induced metallization were investigated.

This work deals with the study of the role of the film thickness and composition on the color selectivity of the collecting spectrum of glass/ZnO:Ga/p-a-Si1-xCx:H/ a-Si1-x C x:H /a-Si:H/n-a-Si:H/Al photoelectronic detectors produced in a single chamber plasma enhanced chemical vapor deposition (PECVD) system. The cross contaminations were minimized by a rotate-cover substrate holder system. The devices can detect the blue illumination at small reverse bias and detect red illumination at large reverse bias. The role of the process parameters, especially the thickness of the p-type and intrinsic a-Si1-x C x:H, and the intrinsic a-Si:H layers on the device performances were studied in detail aiming to achieve a better detectivity. © 2005 Materials Research Society.

A series of hydrogenated amorphous silicon carbide (a-SiC:H) films was prepared by plasma enhanced chemical vapor deposition (PECVD) technology. The microstructure and photoelectronic properties of the film are investigated by absorption spectra (in the ultraviolet to near-infrared range) and Fourier transform infrared (FTIR) spectra. The results show that good band gap controllability (1.83-3.64 eV) was achieved by adjusting the plasma parameters. In the energy range around 2.1 eV, the a-Si1-xCx:H films exhibit good photosensitivity, opening the possibility to use this wide band gap material for device application, especially when blue color detectors are concerned. A multilayer device with a stack of glass/TCO(ZnO:Ga)/P(a-SiC:H)/I(a- SiC:H)/N(a-Si:H)/I(a-Si:H)/P(a-Si:H)/Al has been prepared. The devices can detect blue and red colors under different bias voltages. The optimization of the device, especially the film thickness and the band gap offset used to achieve better detectivity, is also done in this work. © 2005 Elsevier B.V. All rights reserved.

A series of hydrogenated amorphous silicon carbide (a-Si 1- xC x:H) films were prepared by plasma-enhanced chemical vapour deposition (PECVD) using a gas mixture of silane, methane, and hydrogen as the reactive source. The previous results show that a high excitation frequency, together with a high hydrogen dilution ratio of the reactive gases, allow an easier incorporation of the carbon atoms into the silicon-rich a-Si 1-xC x:H film, widen the valence controllability. The data show that films with optical gaps ranging from about 1.9 to 3.6 eV could be produced. In this work the influence of the hydrogen dilution ratio of the reactive gases on the a-Si 1-xC x:H film properties was investigated. The microstuctural and photoelectronic properties of the silicon carbide films were characterized by Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), and FT-IR spectrometry. The results show that a higher hydrogen dilution ratio enhances the incorporation of silicon atoms in the amorphous carbon matrix for carbon-rich a-Si 1-xC x:H films. One pin structure was prepared by using the a-Si 1-xC x:H film as the intrinsic layer. The light spectral response shows that this structure fits the requirement for the top junction of colour sensor. © 2004 Elsevier B.V. All rights reserved.

Polymorphous silicon (pm-Si:H) films have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the pm-Si:H has higher photoconductivity (σph), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. There are a blue shift for the stretching mode of IR. spectra and a red shift for the wagging mode. The shifts are attributed to the variation of the microstructure. By using pm-Si:H film as intrinsic layer, a p-i-n junction solar cell was prepared with the initial efficiency of 8.51% and a stabilized efficiency of 8.01% (AM1.5, 100mw/cm2) at room temperature (T R).

A series of hydrogenated amorphous silicon carbide films were prepared by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of silane, methane, and hydrogen as the reactive source and an excitation frequency of 27.12 MHz. Compared to the typical radio frequency deposition technique, the very high plasma excitation frequency increases the density of the electrons and decreases the electron temperature, which helps the dissociation of the SiH4 and CH4, and reduces the energetic ion impact on the growth surface of the thin film. Thus, dense-films with lower bulk density of states and higher growth rate are expected, as confirmed by spectroscopic ellipsometry data. Apart from that, a substantial reduction of bulk defects is achieved, allowing an improvement of the valence controllability (widening of the optical gap from about 1.9 to 3.6 eV). In this work results concerning the microstuctural and photoelectronic properties of the silicon carbide films will be discussed in detail, correlating them with the deposition process conditions used as well as with the gas phase composition of the mixtures used. © 2004 Elsevier B.V. All rights reserved.

A series of silicon film samples were prepared by plasma enhanced chemical vapor deposition (PECVD) near the threshold from amorphous to nanocrystalline state by adjusting the plasma parameters and properly increasing the reactions between the hydrogen plasma and the growing surface. The microstucture of the films was studied by micro-Raman and Fourier transform infrared (FTIR) spectroscopy. The influences of the hydrogen dilution ratio of silane (R H = [H2]/[SiH4]) and the substrate temperature (Ts) on the microstructural and photoelectronic properties of silicon films were investigated in detail. With the increase of RH from 10 to 100, a notable improvement in the medium-range order (MRO) of the films was observed, and then the phase transition from amorphous to nanocrystalline phase occurred, which lead to the formation of diatomic hydrogen complex, H 2 * and their congeries. With the increase of T s from 150 to 275 °C, both the short-range order and the medium range order of the silicon films are obviously improved. The photoconductivity spectra and the light induced changes of the films show that the diphasic nc-Si/a-Si:H films with fine medium-range order present a broader light spectral response range in the longer wavelength and a lower degradation upon illumination than conventional a-Si:H films. © 2004 Elsevier B.V. All rights reserved.