Valladolid, Spain
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Bilousov O.V.,Rovira i Virgili University | Carvajal J.J.,Rovira i Virgili University | Geaney H.,University College Cork | Geaney H.,Tyndall National Institute | And 9 more authors.
ACS Applied Materials and Interfaces | Year: 2014

Porous GaN based LEDs produced by corrosion etching techniques demonstrated enhanced light extraction efficiency in the past. However, these fabrication techniques require further postgrown processing steps, which increases the price of the final system. Also, the penetration depth of these etching techniques is limited, and affects not only the semiconductor but also the other elements constituting the LED when applied to the final device. In this paper, we present the fabrication of fully porous GaN p-n junctions directly during growth, using a sequential chemical vapor deposition (CVD) process to produce the different layers that form the p-n junction. We characterized their diode behavior from room temperature to 673 K and demonstrated their ability as current rectifiers, thus proving the potential of these fully porous p-n junctions for diode and LEDs applications. The electrical and luminescence characterization confirm that high electronic quality porous structures can be obtained by this method, and we believe this investigation can be extended to other III-N materials for the development of white light LEDs, or to reduce reflection losses and narrowing the output light cone for improved LED external quantum efficiencies. © 2014 American Chemical Society.


Martinez O.,GdS Optronlab | Hortelano V.,GdS Optronlab | Jimenez J.,GdS Optronlab | Parra V.,Grupo Pevafersa | And 3 more authors.
Journal of Electronic Materials | Year: 2010

GaInP, an essential material for multijunction structures of III-V compounds for solar cells, can achieve better photovoltaic responses when grown on (111)GaAs faces, due to the large internal electric fields generated by the off-diagonal strain. In this work, we explored metalorganic chemical vapor deposition growth of GaInP layers on (001)-, (111)Ga-, and (111)As-GaAs substrates, using different phosphine flow rates. The structural and optical properties of the layers have been studied by micro-Raman spectroscopy, microphotoluminescence, and cathodoluminescence. Problems such as composition control, growth rate, and the presence of ordered phases are addressed. © 2010 TMS.


Martin-Martin A.,GdS Optronlab | Jimenez J.,GdS Optronlab
IEEE Photonic Society 24th Annual Meeting, PHO 2011 | Year: 2011

Improving the reliability of high power laser diodes is a crucial issue for their practical application. The understanding of the mechanisms behind the degradation of high power laser diodes is necessary to increase their power and lifetime. The study of the degradation mechanisms requires the investigation of the main defects generated during the laser degradation; therefore, an exhaustive examination of the defect signatures in the degraded devices must be crucial to establish reliable degradation scenarios. Cathodoluminescence (CL) is a unique tool to identify the main defects generated by the device degradation, which will permit to build up a model providing a comprehensive scenario of the laser degradation. CL images of the degraded devices reveal the presence of regions with low, or fully quenched, radiative activity, associated with the presence of extended defects in the active layers of the laser structure, in both the front facet and the cavity. © 2011 IEEE.


Moralejo B.,GdS Optronlab | Hortelano V.,GdS Optronlab | Gonzalez M.A.,GdS Optronlab | Martinez O.,GdS Optronlab | And 3 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2011

In this work we present LBIC measurements of a set of commercial multicrystalline silicon samples manufac-tured by different suppliers. The LBIC measurements were obtained with a home-made system, using several excitation wavelengths, equipped with an autofocus system, and controlling the reflected light. This system keeps constant the distance between the microscope objective and the sample, despite the bowing and the surface roughness characteristic of this type of samples. For the calculation of the Leff maps one needs to consider the distribution of the reflected light, which the maps usually show contrasts corresponding to the different grain orientations. The LBIC maps present networks of dark lines, corresponding to regions with high carrier capture rates. The dark line network does not necessarily match the grain boundaries (GB) revealed in the optical images, but many of them are intragarin defects. The trapping activity of the GB is known to depend on the GB angle. Usually, small angle GBs are decorated with defects that make them electrically active, while the large angles GBs are less decorated, and present a weak electrical activity. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Moralejo B.,GdS Optronlab | Gonzalez M.A.,GdS Optronlab | Jimenez J.,GdS Optronlab | Parra V.,Instalaciones Pevafersa S. L. Energias Renovables | And 3 more authors.
Journal of Electronic Materials | Year: 2010

Multicrystalline silicon (mc-Si) is increasingly used in the photovoltaic industry. However, this material is characterized by intrinsic structural heterogeneities (dislocations, grain boundaries, etc. ), which are detrimental to the performance of the cells. The minority-carrier diffusion length is sensitive to these defects, and gives an indication of the material quality and its suitability for solar cell use. The laser beam induced current (LBIC) technique makes it possible to estimate the local minority-carrier diffusion length from photocurrent contrast data. The purpose of this work is to show an advanced homemade LBIC system that highlights the importance of controlling the laser power excitation and the reflected light in inhomogeneous mc-Si samples. This control demonstrates that the estimated minority-carrier diffusion length (L Diff) in texturized multicrystalline wafers strongly depends on the collecting conditions of the reflected light. © 2010 TMS.


Plaza J.L.,Autonomous University of Madrid | Martinez O.,GdS Optronlab | Rubio S.,Autonomous University of Madrid | Hortelano V.,GdS Optronlab | Dieguez E.,Autonomous University of Madrid
CrystEngComm | Year: 2013

The growth of CdTe/CdS films by a close space sublimation (CSS) technique using SiC electrical heating elements is presented. The structure, composition and optical properties of the films are studied as a function of different growth parameters and compared with previous results reported in the literature from films grown by CSS using halogen lamps. The homogeneity and composition of the films are analyzed by scanning electron microscopy, grazing angle (0.5°) X-Ray diffraction and energy dispersive analysis. Electron beam induced current is also used for the preliminary analysis of the CdTe/CdS junctions. © 2013 The Royal Society of Chemistry.


Martinez-Tomas M.C.,University of Valencia | Hortelano V.,GdS Optronlab | Jimenez J.,GdS Optronlab | Wang B.,Solid State Scientific Corporation | Munoz-Sanjose V.,University of Valencia
CrystEngComm | Year: 2013

The goal of this work is to show the capability of X-ray multiple diffraction (XRMD) to be used in combination with high resolution X-ray diffraction (HRXRD) and cathodoluminescence (CL) as an easy and simple methodology to determine structural and surface defect-related characteristics of samples that could be used as substrates for epitaxial growth. For this study ZnO {0001}-oriented samples have been used in view of their use as substrates for homoepitaxy. The miscut and bending of the samples have been analyzed by measuring the position of the X-ray diffraction peaks. The presence of multiple crystallographic domains and their characteristics have been studied by HRXRD (from the allowed (0002) reflection) and XRMD (from the forbidden (0001) and (0003) reflections) through Renninger scans and omega-scans. Cathodoluminescence adds to the previous structural characterization the possibility of obtaining significant information on surface and bulk defect-related optical properties by means of probe depth modulation. Thus, the combined methodology using HRXRD, XRMD and CL shows its ability to assess the structural and surface defect-related properties of substrates, allowing an easy detection of subtle structural and surface defects that can affect the ulterior use of these substrates in epitaxial growth. © 2013 The Royal Society of Chemistry.


Torres A.,GdS Optronlab | Martin-Martin A.,GdS Optronlab | Martinez O.,GdS Optronlab | Prieto A.C.,GdS Optronlab | And 5 more authors.
Applied Physics Letters | Year: 2010

Raman spectroscopy provides nondestructive information about nanoscaled semiconductors by modeling the phonon confinement effect. However, the Raman spectrum is also sensitive to the temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present an analysis of the Raman spectra of Si nanowires (NWs). The influence of the excitation conditions and the temperature increase in the NWs are discussed. The interpretation of the data is supported by the calculation of the temperature inside the NWs with different diameters. © 2010 American Institute of Physics.


Anaya J.,GdS Optronlab | Prieto A.C.,GdS Optronlab | Martinez O.,GdS Optronlab | Torres A.,GdS Optronlab | And 5 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2011

Group IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. The Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for Si and SiGe nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Moralejo B.,GdS Optronlab | Tejero A.,GdS Optronlab | Hortelano V.,GdS Optronlab | Martinez O.,GdS Optronlab | And 2 more authors.
Superlattices and Microstructures | Year: 2016

Multicristalline Silicon (mc-Si) is the preferred material for current terrestrial photovoltaic applications. However, the high density of defects present in mc-Si deteriorates the material properties, in particular the minority carrier diffusion length. For this reason, a large effort to characterize the mc-Si material is demanded, aiming to visualize the defective areas and to quantify the type of defects, density and its origin. In this work, several complementary light and electron probe techniques are used for the analysis of both mc-Si wafers and solar cells. These techniques comprise both fast and whole-area detection techniques such as Photoluminescence imaging, and highly spatially resolved time consuming techniques, such as light and electron beam induced current techniques and μRaman spectroscopy. These techniques were applied to the characterization of different mc-Si wafers for solar cells, e.g. ribbon wafers, cast mc-Si as well as quasi-monocrystalline material, upgraded metallurgical mc-Si wafers, and finished solar cells. © 2016 Elsevier Ltd.

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