K. Leyva - Academia.edu (original) (raw)

Papers by K. Leyva

Research paper thumbnail of Optical, morphological and electrical analysis of heterostructures PSi/c-Si and SiO2/MWCNTs/PSi/c-Si

Sensors and Actuators A: Physical, 2018

Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visib... more Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visible range at room temperature. PSi layers are useful for various optical and electrical applications among others. The PSi properties can be enhanced using different materials. In the present work, we have decorated PSi single layers with multiple wall carbon nanotubes (MWCNTs). The thickness of PSi layers was determined by the gravimetric analysis, the surface morphology by scanning electron microscopy (SEM), the optical properties were studied by measuring PL and reflectance spectra and the electrical behavior was analyzed from the measured I-V curves for which some theoretical transport mechanisms are used to make a study in depth. These materials and structures have potential applications in chemical sensors.

Research paper thumbnail of Optical, morphological and electrical analysis of heterostructures PSi/c-Si and SiO2/MWCNTs/PSi/c-Si

Sensors and Actuators A: Physical, 2018

Abstract Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in ... more Abstract Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visible range at room temperature. PSi layers are useful for various optical and electrical applications among others. The PSi properties can be enhanced using different materials. In the present work, we have decorated PSi single layers with multiple wall carbon nanotubes (MWCNTs). The thickness of PSi layers was determined by the gravimetric analysis, the surface morphology by scanning electron microscopy (SEM), the optical properties were studied by measuring PL and reflectance spectra and the electrical behavior was analyzed from the measured I–V curves for which some theoretical transport mechanisms are used to make a study in depth. These materials and structures have potential applications in chemical sensors.

Research paper thumbnail of Blue and red electroluminescence of silicon-rich oxide light emitting capacitors

Electroluminescent properties of thin silicon-rich oxide (SRO) films deposited by low pressure ch... more Electroluminescent properties of thin silicon-rich oxide (SRO) films deposited by low pressure chemical vapor deposition (LPCVD) were studied. The gas flow ratio Ro = N2O/SiH4 was changed to obtain different silicon concentrations within the SRO films. After deposition, SRO films were thermally annealed at 1100ºC for 3h in N2 atmosphere in order to create silicon nanoparticles (Si-nps). Simple capacitive structures

Research paper thumbnail of Strong blue and red luminescence in silicon nanoparticles based light emitting capacitors

Applied Physics Letters, 2011

Research paper thumbnail of Topographic analysis of silicon nanoparticles-based electroluminescent devices

Materials Science and Engineering: B, 2010

Electroluminescent properties of silicon nanoparticles embedded in MOS devices have been studied.... more Electroluminescent properties of silicon nanoparticles embedded in MOS devices have been studied. Silicon rich oxide (SRO) films with 4 at.% of silicon excess were used as active layers. Intense and stable light emission is observed with the naked eye as shining spots at the surface of devices. AFM measurements on these devices exhibit a remarkably granular surface where the EL spots are observed. The EL measurements show a broad visible spectrum with various peaks between 420 and 870 nm. These EL spots are related with charge injection through conductive paths created by adjacent Si-nps within the SRO.

Research paper thumbnail of Structural and o ptical p roperties of a new s oluble e rbium (III) octa - substituted bis - p hthalocyanine c omplex

In this study a sandwich - type octa - substituted Erbium (III) bis - phthalocyanine compound of ... more In this study a sandwich - type octa - substituted Erbium (III) bis - phthalocyanine compound of increased solubility was synthetized from a metal free phthalocyanine with the same substitution pattern using strictly dry reaction conditions. Then the pure pro duct obtained from a chromatographic purification method was de posited as thin films by spin coating onto glass substrates to investigate its structural and optical properties. The UV - Vis spectrum shows the intense characteristic peaks of this kind of phthalocyanine compounds, particularly in the range from 560 to 630 nm. The chemical nature of the thin film material was corroborated through x - ray diffraction analysis and IR spectroscopy. Photoluminescence emission was observed for the films in the visible range.

Research paper thumbnail of As-growth and Annealing Porous Silicon Mirrors for Optical Applications in the UV

International Journal on Smart Sensing and Intelligent Systems

This work presents a study of the evolution of the reflectance spectra of porous silicon as-growt... more This work presents a study of the evolution of the reflectance spectra of porous silicon as-growth and with thermal oxidation under controlled conditions. Porous silicon layers were prepared by electrochemical anodization of a silicon substrate p+ in an aqueous solution of hydrofluoric acid and ethanol. Multilayer structures were formed on the basis of porous silicon, two different layers were realized by controlling the refraction index of each one of the layers using the Bruggemann model, in this case for multilayer as-growth, and subsequently a dry oxidation was performed to observe the change in refractive index and reflectance. A model that contains the refractive index of silicon, air and silicon oxide is used for predicting the behavior of the reflectance spectra. With this model is possible to control the width of the reflectance spectrum of the band pass or also called Distributed Bragg Reflector (DBR), DBR were characterized and measured by SEM and UV-VIS spectroscopy. Reflectance spectra were obtained and we can see that the annealing provoked a shifted towards the ultra violet (UV). These changes on reflectance and refractive indexes indicate that oxidation processes can modify the multilayer porous silicon. The optical band gap energy (Eg) was obtained from 4.36 to 3.98 eV to the DBR. These low cost devices open the way to the development of optical sensing in UV entirely based on silicon.

Research paper thumbnail of CZTS solar cells and the possibility of increasing VOC using evaporated Al2O3 at the CZTS/CdS interface

Solar Energy

Abstract We report the effect of an ultra-thin Al2O3 layer (down to 3 nm) as interface passivatio... more Abstract We report the effect of an ultra-thin Al2O3 layer (down to 3 nm) as interface passivation strategy for the improvement of the performance of Cu2ZnSnS4/CdS based solar cells. After an initial optimization, the Al2O3 deposited by thermal evaporation is proved to improve the properties of the p-n junction. The fabricated devices showed an increment in Voc depending on the composition of the absorber, and an improvement in fill factor (FF) apparently related to the insulation of possible shunt-paths. Also, the impact on other optoelectronic parameters is discussed.

Research paper thumbnail of Photoluminescence comparison of SRO-LPCVD films deposited on quartz, polysilicon and silicon substrates

Journal of Luminescence

Abstract In the present work, photoluminescence spectra of silicon-rich oxide monolayers (SRO10 a... more Abstract In the present work, photoluminescence spectra of silicon-rich oxide monolayers (SRO10 and SRO25) and bilayers (SRO25/10, SRO10/25) films deposited on quartz, polysilicon on quartz and silicon substrates are compared. Silicon-rich oxide films were deposited using Low Pressure Chemical Vapor Deposition (LPCVD) technique. The films were characterized by Ellipsometry, Fourier Transform Infrared Spectroscopy, Secondary Ion Mass Spectrometry, Optical Transmittance, Photoluminescence, Scanning Electron Microscope, and High-Resolution Transmission Electron Microscopy. The results show that the bilayer films, deposited on polysilicon film on quartz have the stronger photoluminescence, which is indicative that there are different types of defects, Silicon nanocrystals, Silicon nanoparticles, and amorphous silicon nanoparticles that improve the Photoluminescence response. Also, it was observed constructive interferences in the transmittance a spectrum of silicon-rich oxide films/polysilicon films on quartz, due to that their refractive indices are different and they are together. This, when a beam of light crosses the interface between materials with different refraction indexes, its direction of propagation is altered, and the bigger is the difference of its refractive indexes, the greater will be the beam refraction. In all materials known this phenomenon is called as positive refraction. The photoluminescence is related to silicon dioxide defects such as weak oxygen bonds, neutral oxygen vacancy, non-bridging oxygen hole centers, or positively charged oxygen vacancies. Moreover, it is a combined effect where the bandgap energy acquires some direct bandgap properties due to quantum confinement, both effects (defects and quantum confinement) are important to increase the photoluminescence intensity. The average diameters of Silicon nanocrystals were estimated from the band gap energy and also by High-Resolution Transmission Electron Microscopy obtaining an average diameter of 3.8 ± 0.08 nm. Comparative analysis of optical and structural properties was performed on all samples.

Research paper thumbnail of The evolution of the crystallinity depending on the annealing temperature in the CTS films obtained by Spray Pyrolysis

Materials Research Express

Research paper thumbnail of Optical, morphological and electrical analysis of heterostructures

Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visib... more Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visible range at room temperature. PSi layers are useful for various optical and electrical applications among others. The PSi properties can be enhanced using different materials. In the present work, we have decorated PSi single layers with multiple wall carbon nanotubes (MWCNTs). The thickness of PSi layers was determined by the gravimetric analysis, the surface morphology by scanning electron microscopy (SEM), the optical properties were studied by measuring PL and reflectance spectra and the electrical behavior was analyzed from the measured I-V curves for which some theoretical transport mechanisms are used to make a study in depth. These materials and structures have potential applications in chemical sensors.

Research paper thumbnail of Down-Conversion Effect Created by SiOx Films Obtained by HFCVD and Applied over Pn-Junctions

Silicon

A top coating film of silicon oxide off-stoichiometry (SiOx) was used on silicon solar cells to i... more A top coating film of silicon oxide off-stoichiometry (SiOx) was used on silicon solar cells to improve its electrical properties by the Down-conversion effect. The SiOx films were obtained by hot filament chemical vapor deposition (HFCVD) with different hydrogen flow (HF) and different distances: the wire-source distance and the source-substrate distance, and by consequence, with different temperatures. Transmittance spectra showed 0% of transmittance in the UV region. The amount of atomic silicon % in the SiOx films was changed with the variation of the mentioned parameters, as demonstrated with the Energy-Dispersive X-ray Spectroscopy (EDS) and the Fourier transform infrared spectroscopy (FTIR) results. The SiOx films showed a wide Photoluminescence (PL) between 400 nm and 900 nm when they were excited with UV light. The SiOx films were applied as a top coating on pn junctions of silicon substrate to develop silicon solar cells. The J-V measurements and the external quantum efficiency (EQE) of the solar cells were obtained, as well as the open circuit voltage (Voc), short-circuit current density (Jsc), the efficiency (η) and the fill factor (FF). The silicon solar cells with the SiOx top coatings, with the highest PL, showed the highest efficiency. The best figures of merit were η = 5.9%, Voc = 480 mV, Jsc = 27 mA/cm2, Pmax = 5.5 mW and FF = 0.4.

Research paper thumbnail of Study of narrow and intense UV electroluminescence from ITO/SRO/Si-p and ITO/SRN/SRO/Si-p based light emitting capacitors

Journal of Luminescence

Abstract In this work, multiple narrow and highly intense ultraviolet (UV) electroluminescent (EL... more Abstract In this work, multiple narrow and highly intense ultraviolet (UV) electroluminescent (EL) bands were observed in light emitting capacitors (LECs) using silicon rich oxide (SRO) films as active layer. Besides, the effect of a thin silicon rich nitride (SRN) film on top of the SRO (as SRN/SRO bilayer) layer was also studied. LECs were fabricated using simple metal–insulator–semiconductor (MIS) structures with indium tin oxide (ITO) and aluminum as gate and substrate electrodes, respectively. SRO and SRN films contain 41.85±1.1 and 46.96±1.1 at% of silicon, respectively. Both structures exhibited a resistance switching (RS) behavior from a high conduction state (HCS) to a low conduction state (LCS), enhancing an intense UV EL. This RS behavior produces structural changes in the active layer and probably in the ITO contact. Seven narrow bands with half-peak width of 7±0.6 nm at ~250, 270, 285, 305, 325, 415 and 450 nm were clearly observed once the LCS was reached. These bands could be related to a combination of emissions through defects inside SRO (252, 288.2 and 415 nm), and characteristic radiation of neutral tin (252.39 and 286.33 nm), neutral indium (271.02, 303.93 and 325.85 nm), single (444.82 nm) and doubly ionized indium (403.07 nm). Furthermore, red EL was observed at the HCS and it was similar to the PL spectra indicating the same radiative process involved. The charge transport is improved when the SRN/SRO bilayer is used as active layer in the LEC. An EL band at ~590 nm is observed when the SRN/SRO bilayer is formed at both conduction states. This band has been observed before and attributed to transitions from the minimum conduction band to K° centers in SRN films. The conduction mechanism responsible of the EL at both conduction states was also studied.

Research paper thumbnail of Visible electroluminescence on FTO/thin SRO/n-Si structures

Materials Science and Engineering: B, 2010

Photoluminescence (PL) and electroluminescence (EL) of silicon rich oxide (SRO) films deposited b... more Photoluminescence (PL) and electroluminescence (EL) of silicon rich oxide (SRO) films deposited by low pressure chemical vapour deposition (LPCVD) have been researched. SRO films emit an intense PL band between 550 and 850 nm. EL was studied using fluorine-doped tin oxide (FTO)/thin SRO/n-Si structures. Intense and stable electroluminescence was observed under reverse bias. EL is observed between 400 and 900 nm with two main peaks around 450 and 600 nm. EL was related to charge injection through conductive paths and radiative recombination between traps or defect levels.

Research paper thumbnail of On the photoluminescence of multilayer arrays of silicon rich oxide with high silicon content prepared by low pressure chemical vapor deposition

The photoluminescence emission of multilayer structures composed of layers of silicon rich oxide ... more The photoluminescence emission of multilayer structures composed of layers of silicon rich oxide with high silicon content and layers of silicon rich oxide with low silicon content obtained by low pressure chemical vapor deposition is here presented. Different parameters for the preparation of the multilayers have been varied such as the Si concentration and the thicknesses of the layers. Additionally, the samples were oxidized at different temperatures. For all samples the photoluminescence seems to have the same origin: defects in the oxide matrix and defects at the interfaces between the Si nanocrystals. The structural and compositional properties of the multilayer structures are discussed.

Research paper thumbnail of Strong blue and red luminescence in silicon nanoparticles based light emitting capacitors

Below are the queries associated with your article; please answer all of these queries before sen... more Below are the queries associated with your article; please answer all of these queries before sending the proof back to AIP. Author please indicate the correct color processing option from the list below: 1. Author, please confirm Figure number(s) that should appear as color in print. Please know that any associated mandatory fees will apply for figures printed in color. Location in article Query / Remark: click on the Q link to navigate to the appropriate spot in the proof. There, insert your comments as a PDF annotation.

Research paper thumbnail of Blue and red electroluminescence of silicon-rich oxide light emitting capacitors

Electroluminescent properties of thin silicon-rich oxide (SRO) films deposited by low pressure ch... more Electroluminescent properties of thin silicon-rich oxide (SRO) films deposited by low pressure chemical vapor deposition (LPCVD) were studied. The gas flow ratio Ro = N2O/SiH4 was changed to obtain different silicon concentrations within the SRO films. After deposition, SRO films were thermally annealed at 1100ºC for 3h in N2 atmosphere in order to create silicon nanoparticles (Si-nps). Simple capacitive structures

Research paper thumbnail of High efficiency Cu2ZnSnS4 solar cells over FTO substrates and their CZTS/CdS interface passivation via thermal evaporation of Al2O3

Journal of Materials Chemistry C

Sulfur kesterite (CZTS) solar cells on transparent substrate (FTO) showing η = 7.3% and Voc = 700... more Sulfur kesterite (CZTS) solar cells on transparent substrate (FTO) showing η = 7.3% and Voc = 700 mV (structure: SLG/FTO/Mo (20 nm)/CZTS/Al2O3/CdS/i-ZnO/ITO) and η = 7.7% and Voc = 677 mV (structure: SLG/FTO/Mo (20 nm)/CZTS/CdS/i-ZnO/ITO).

Research paper thumbnail of MOS-like electroluminescent devices using silicon-rich oxide obtained by LPCVD

Silicon Rich Oxide (SRO) is a multiphase material composed by SiO2, Si and SiOx.(0<X<2) SRO... more Silicon Rich Oxide (SRO) is a multiphase material composed by SiO2, Si and SiOx.(0<X<2) SRO characteristics include the photo and cathode emission of visible light. Lastly, big efforts have been devoted to obtain a controllable emission using electroluminescence, but keeping its compatibility with silicon IC's fabrication technology. In this paper, electroluminescent properties of PolySi/SRO/Si structures were studied. Devices with two different Si excesses were characterized. A full area wideband emission is found on devices with the highest Si excess, the principal emitting bands are centered at 475 and 670 nm. The EL intensity of these bands is modulated by the applied electric field. Different emission colors were observed with the naked eye. The 670 band present in devices with the highest Si excess is not found in those with the lowest Si excess. A discussion on the probable mechanism of emission is presented.

Research paper thumbnail of Photoluminescence enhancement through silicon implantation on SRO-LPCVD films

Materials Science and Engineering: B, 2010

Photoluminescence (PL) properties of thin and thick silicon-rich oxide (SRO) and silicon implante... more Photoluminescence (PL) properties of thin and thick silicon-rich oxide (SRO) and silicon implanted SRO (SI-SRO) films with different silicon excess fabricated by low pressure chemical vapor deposition (LPCVD) were studied. The effects of the annealing temperature and silicon implantation on the PL were also studied. Maximum luminescence intensity was observed with an annealing temperature of 1150 and 1100 • C for thin and thick SRO films, respectively. The PL intensity is strongly enhanced when SRO films are implanted with silicon, especially for thin SRO films. Thin SI-SRO films emit up to six times more than non-implanted films, meanwhile the PL in thick SI-SRO films is only improved less than two times. Therefore, thin SI-SRO films are an interesting alternative for applications such as the fabrication of efficient Si-nps based LEDs.

Research paper thumbnail of Optical, morphological and electrical analysis of heterostructures PSi/c-Si and SiO2/MWCNTs/PSi/c-Si

Sensors and Actuators A: Physical, 2018

Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visib... more Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visible range at room temperature. PSi layers are useful for various optical and electrical applications among others. The PSi properties can be enhanced using different materials. In the present work, we have decorated PSi single layers with multiple wall carbon nanotubes (MWCNTs). The thickness of PSi layers was determined by the gravimetric analysis, the surface morphology by scanning electron microscopy (SEM), the optical properties were studied by measuring PL and reflectance spectra and the electrical behavior was analyzed from the measured I-V curves for which some theoretical transport mechanisms are used to make a study in depth. These materials and structures have potential applications in chemical sensors.

Research paper thumbnail of Optical, morphological and electrical analysis of heterostructures PSi/c-Si and SiO2/MWCNTs/PSi/c-Si

Sensors and Actuators A: Physical, 2018

Abstract Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in ... more Abstract Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visible range at room temperature. PSi layers are useful for various optical and electrical applications among others. The PSi properties can be enhanced using different materials. In the present work, we have decorated PSi single layers with multiple wall carbon nanotubes (MWCNTs). The thickness of PSi layers was determined by the gravimetric analysis, the surface morphology by scanning electron microscopy (SEM), the optical properties were studied by measuring PL and reflectance spectra and the electrical behavior was analyzed from the measured I–V curves for which some theoretical transport mechanisms are used to make a study in depth. These materials and structures have potential applications in chemical sensors.

Research paper thumbnail of Blue and red electroluminescence of silicon-rich oxide light emitting capacitors

Electroluminescent properties of thin silicon-rich oxide (SRO) films deposited by low pressure ch... more Electroluminescent properties of thin silicon-rich oxide (SRO) films deposited by low pressure chemical vapor deposition (LPCVD) were studied. The gas flow ratio Ro = N2O/SiH4 was changed to obtain different silicon concentrations within the SRO films. After deposition, SRO films were thermally annealed at 1100ºC for 3h in N2 atmosphere in order to create silicon nanoparticles (Si-nps). Simple capacitive structures

Research paper thumbnail of Strong blue and red luminescence in silicon nanoparticles based light emitting capacitors

Applied Physics Letters, 2011

Research paper thumbnail of Topographic analysis of silicon nanoparticles-based electroluminescent devices

Materials Science and Engineering: B, 2010

Electroluminescent properties of silicon nanoparticles embedded in MOS devices have been studied.... more Electroluminescent properties of silicon nanoparticles embedded in MOS devices have been studied. Silicon rich oxide (SRO) films with 4 at.% of silicon excess were used as active layers. Intense and stable light emission is observed with the naked eye as shining spots at the surface of devices. AFM measurements on these devices exhibit a remarkably granular surface where the EL spots are observed. The EL measurements show a broad visible spectrum with various peaks between 420 and 870 nm. These EL spots are related with charge injection through conductive paths created by adjacent Si-nps within the SRO.

Research paper thumbnail of Structural and o ptical p roperties of a new s oluble e rbium (III) octa - substituted bis - p hthalocyanine c omplex

In this study a sandwich - type octa - substituted Erbium (III) bis - phthalocyanine compound of ... more In this study a sandwich - type octa - substituted Erbium (III) bis - phthalocyanine compound of increased solubility was synthetized from a metal free phthalocyanine with the same substitution pattern using strictly dry reaction conditions. Then the pure pro duct obtained from a chromatographic purification method was de posited as thin films by spin coating onto glass substrates to investigate its structural and optical properties. The UV - Vis spectrum shows the intense characteristic peaks of this kind of phthalocyanine compounds, particularly in the range from 560 to 630 nm. The chemical nature of the thin film material was corroborated through x - ray diffraction analysis and IR spectroscopy. Photoluminescence emission was observed for the films in the visible range.

Research paper thumbnail of As-growth and Annealing Porous Silicon Mirrors for Optical Applications in the UV

International Journal on Smart Sensing and Intelligent Systems

This work presents a study of the evolution of the reflectance spectra of porous silicon as-growt... more This work presents a study of the evolution of the reflectance spectra of porous silicon as-growth and with thermal oxidation under controlled conditions. Porous silicon layers were prepared by electrochemical anodization of a silicon substrate p+ in an aqueous solution of hydrofluoric acid and ethanol. Multilayer structures were formed on the basis of porous silicon, two different layers were realized by controlling the refraction index of each one of the layers using the Bruggemann model, in this case for multilayer as-growth, and subsequently a dry oxidation was performed to observe the change in refractive index and reflectance. A model that contains the refractive index of silicon, air and silicon oxide is used for predicting the behavior of the reflectance spectra. With this model is possible to control the width of the reflectance spectrum of the band pass or also called Distributed Bragg Reflector (DBR), DBR were characterized and measured by SEM and UV-VIS spectroscopy. Reflectance spectra were obtained and we can see that the annealing provoked a shifted towards the ultra violet (UV). These changes on reflectance and refractive indexes indicate that oxidation processes can modify the multilayer porous silicon. The optical band gap energy (Eg) was obtained from 4.36 to 3.98 eV to the DBR. These low cost devices open the way to the development of optical sensing in UV entirely based on silicon.

Research paper thumbnail of CZTS solar cells and the possibility of increasing VOC using evaporated Al2O3 at the CZTS/CdS interface

Solar Energy

Abstract We report the effect of an ultra-thin Al2O3 layer (down to 3 nm) as interface passivatio... more Abstract We report the effect of an ultra-thin Al2O3 layer (down to 3 nm) as interface passivation strategy for the improvement of the performance of Cu2ZnSnS4/CdS based solar cells. After an initial optimization, the Al2O3 deposited by thermal evaporation is proved to improve the properties of the p-n junction. The fabricated devices showed an increment in Voc depending on the composition of the absorber, and an improvement in fill factor (FF) apparently related to the insulation of possible shunt-paths. Also, the impact on other optoelectronic parameters is discussed.

Research paper thumbnail of Photoluminescence comparison of SRO-LPCVD films deposited on quartz, polysilicon and silicon substrates

Journal of Luminescence

Abstract In the present work, photoluminescence spectra of silicon-rich oxide monolayers (SRO10 a... more Abstract In the present work, photoluminescence spectra of silicon-rich oxide monolayers (SRO10 and SRO25) and bilayers (SRO25/10, SRO10/25) films deposited on quartz, polysilicon on quartz and silicon substrates are compared. Silicon-rich oxide films were deposited using Low Pressure Chemical Vapor Deposition (LPCVD) technique. The films were characterized by Ellipsometry, Fourier Transform Infrared Spectroscopy, Secondary Ion Mass Spectrometry, Optical Transmittance, Photoluminescence, Scanning Electron Microscope, and High-Resolution Transmission Electron Microscopy. The results show that the bilayer films, deposited on polysilicon film on quartz have the stronger photoluminescence, which is indicative that there are different types of defects, Silicon nanocrystals, Silicon nanoparticles, and amorphous silicon nanoparticles that improve the Photoluminescence response. Also, it was observed constructive interferences in the transmittance a spectrum of silicon-rich oxide films/polysilicon films on quartz, due to that their refractive indices are different and they are together. This, when a beam of light crosses the interface between materials with different refraction indexes, its direction of propagation is altered, and the bigger is the difference of its refractive indexes, the greater will be the beam refraction. In all materials known this phenomenon is called as positive refraction. The photoluminescence is related to silicon dioxide defects such as weak oxygen bonds, neutral oxygen vacancy, non-bridging oxygen hole centers, or positively charged oxygen vacancies. Moreover, it is a combined effect where the bandgap energy acquires some direct bandgap properties due to quantum confinement, both effects (defects and quantum confinement) are important to increase the photoluminescence intensity. The average diameters of Silicon nanocrystals were estimated from the band gap energy and also by High-Resolution Transmission Electron Microscopy obtaining an average diameter of 3.8 ± 0.08 nm. Comparative analysis of optical and structural properties was performed on all samples.

Research paper thumbnail of The evolution of the crystallinity depending on the annealing temperature in the CTS films obtained by Spray Pyrolysis

Materials Research Express

Research paper thumbnail of Optical, morphological and electrical analysis of heterostructures

Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visib... more Porous silicon (PSi) has been studied extensively due to its photo luminescence (PL) in the visible range at room temperature. PSi layers are useful for various optical and electrical applications among others. The PSi properties can be enhanced using different materials. In the present work, we have decorated PSi single layers with multiple wall carbon nanotubes (MWCNTs). The thickness of PSi layers was determined by the gravimetric analysis, the surface morphology by scanning electron microscopy (SEM), the optical properties were studied by measuring PL and reflectance spectra and the electrical behavior was analyzed from the measured I-V curves for which some theoretical transport mechanisms are used to make a study in depth. These materials and structures have potential applications in chemical sensors.

Research paper thumbnail of Down-Conversion Effect Created by SiOx Films Obtained by HFCVD and Applied over Pn-Junctions

Silicon

A top coating film of silicon oxide off-stoichiometry (SiOx) was used on silicon solar cells to i... more A top coating film of silicon oxide off-stoichiometry (SiOx) was used on silicon solar cells to improve its electrical properties by the Down-conversion effect. The SiOx films were obtained by hot filament chemical vapor deposition (HFCVD) with different hydrogen flow (HF) and different distances: the wire-source distance and the source-substrate distance, and by consequence, with different temperatures. Transmittance spectra showed 0% of transmittance in the UV region. The amount of atomic silicon % in the SiOx films was changed with the variation of the mentioned parameters, as demonstrated with the Energy-Dispersive X-ray Spectroscopy (EDS) and the Fourier transform infrared spectroscopy (FTIR) results. The SiOx films showed a wide Photoluminescence (PL) between 400 nm and 900 nm when they were excited with UV light. The SiOx films were applied as a top coating on pn junctions of silicon substrate to develop silicon solar cells. The J-V measurements and the external quantum efficiency (EQE) of the solar cells were obtained, as well as the open circuit voltage (Voc), short-circuit current density (Jsc), the efficiency (η) and the fill factor (FF). The silicon solar cells with the SiOx top coatings, with the highest PL, showed the highest efficiency. The best figures of merit were η = 5.9%, Voc = 480 mV, Jsc = 27 mA/cm2, Pmax = 5.5 mW and FF = 0.4.

Research paper thumbnail of Study of narrow and intense UV electroluminescence from ITO/SRO/Si-p and ITO/SRN/SRO/Si-p based light emitting capacitors

Journal of Luminescence

Abstract In this work, multiple narrow and highly intense ultraviolet (UV) electroluminescent (EL... more Abstract In this work, multiple narrow and highly intense ultraviolet (UV) electroluminescent (EL) bands were observed in light emitting capacitors (LECs) using silicon rich oxide (SRO) films as active layer. Besides, the effect of a thin silicon rich nitride (SRN) film on top of the SRO (as SRN/SRO bilayer) layer was also studied. LECs were fabricated using simple metal–insulator–semiconductor (MIS) structures with indium tin oxide (ITO) and aluminum as gate and substrate electrodes, respectively. SRO and SRN films contain 41.85±1.1 and 46.96±1.1 at% of silicon, respectively. Both structures exhibited a resistance switching (RS) behavior from a high conduction state (HCS) to a low conduction state (LCS), enhancing an intense UV EL. This RS behavior produces structural changes in the active layer and probably in the ITO contact. Seven narrow bands with half-peak width of 7±0.6 nm at ~250, 270, 285, 305, 325, 415 and 450 nm were clearly observed once the LCS was reached. These bands could be related to a combination of emissions through defects inside SRO (252, 288.2 and 415 nm), and characteristic radiation of neutral tin (252.39 and 286.33 nm), neutral indium (271.02, 303.93 and 325.85 nm), single (444.82 nm) and doubly ionized indium (403.07 nm). Furthermore, red EL was observed at the HCS and it was similar to the PL spectra indicating the same radiative process involved. The charge transport is improved when the SRN/SRO bilayer is used as active layer in the LEC. An EL band at ~590 nm is observed when the SRN/SRO bilayer is formed at both conduction states. This band has been observed before and attributed to transitions from the minimum conduction band to K° centers in SRN films. The conduction mechanism responsible of the EL at both conduction states was also studied.

Research paper thumbnail of Visible electroluminescence on FTO/thin SRO/n-Si structures

Materials Science and Engineering: B, 2010

Photoluminescence (PL) and electroluminescence (EL) of silicon rich oxide (SRO) films deposited b... more Photoluminescence (PL) and electroluminescence (EL) of silicon rich oxide (SRO) films deposited by low pressure chemical vapour deposition (LPCVD) have been researched. SRO films emit an intense PL band between 550 and 850 nm. EL was studied using fluorine-doped tin oxide (FTO)/thin SRO/n-Si structures. Intense and stable electroluminescence was observed under reverse bias. EL is observed between 400 and 900 nm with two main peaks around 450 and 600 nm. EL was related to charge injection through conductive paths and radiative recombination between traps or defect levels.

Research paper thumbnail of On the photoluminescence of multilayer arrays of silicon rich oxide with high silicon content prepared by low pressure chemical vapor deposition

The photoluminescence emission of multilayer structures composed of layers of silicon rich oxide ... more The photoluminescence emission of multilayer structures composed of layers of silicon rich oxide with high silicon content and layers of silicon rich oxide with low silicon content obtained by low pressure chemical vapor deposition is here presented. Different parameters for the preparation of the multilayers have been varied such as the Si concentration and the thicknesses of the layers. Additionally, the samples were oxidized at different temperatures. For all samples the photoluminescence seems to have the same origin: defects in the oxide matrix and defects at the interfaces between the Si nanocrystals. The structural and compositional properties of the multilayer structures are discussed.

Research paper thumbnail of Strong blue and red luminescence in silicon nanoparticles based light emitting capacitors

Below are the queries associated with your article; please answer all of these queries before sen... more Below are the queries associated with your article; please answer all of these queries before sending the proof back to AIP. Author please indicate the correct color processing option from the list below: 1. Author, please confirm Figure number(s) that should appear as color in print. Please know that any associated mandatory fees will apply for figures printed in color. Location in article Query / Remark: click on the Q link to navigate to the appropriate spot in the proof. There, insert your comments as a PDF annotation.

Research paper thumbnail of Blue and red electroluminescence of silicon-rich oxide light emitting capacitors

Electroluminescent properties of thin silicon-rich oxide (SRO) films deposited by low pressure ch... more Electroluminescent properties of thin silicon-rich oxide (SRO) films deposited by low pressure chemical vapor deposition (LPCVD) were studied. The gas flow ratio Ro = N2O/SiH4 was changed to obtain different silicon concentrations within the SRO films. After deposition, SRO films were thermally annealed at 1100ºC for 3h in N2 atmosphere in order to create silicon nanoparticles (Si-nps). Simple capacitive structures

Research paper thumbnail of High efficiency Cu2ZnSnS4 solar cells over FTO substrates and their CZTS/CdS interface passivation via thermal evaporation of Al2O3

Journal of Materials Chemistry C

Sulfur kesterite (CZTS) solar cells on transparent substrate (FTO) showing η = 7.3% and Voc = 700... more Sulfur kesterite (CZTS) solar cells on transparent substrate (FTO) showing η = 7.3% and Voc = 700 mV (structure: SLG/FTO/Mo (20 nm)/CZTS/Al2O3/CdS/i-ZnO/ITO) and η = 7.7% and Voc = 677 mV (structure: SLG/FTO/Mo (20 nm)/CZTS/CdS/i-ZnO/ITO).

Research paper thumbnail of MOS-like electroluminescent devices using silicon-rich oxide obtained by LPCVD

Silicon Rich Oxide (SRO) is a multiphase material composed by SiO2, Si and SiOx.(0<X<2) SRO... more Silicon Rich Oxide (SRO) is a multiphase material composed by SiO2, Si and SiOx.(0<X<2) SRO characteristics include the photo and cathode emission of visible light. Lastly, big efforts have been devoted to obtain a controllable emission using electroluminescence, but keeping its compatibility with silicon IC's fabrication technology. In this paper, electroluminescent properties of PolySi/SRO/Si structures were studied. Devices with two different Si excesses were characterized. A full area wideband emission is found on devices with the highest Si excess, the principal emitting bands are centered at 475 and 670 nm. The EL intensity of these bands is modulated by the applied electric field. Different emission colors were observed with the naked eye. The 670 band present in devices with the highest Si excess is not found in those with the lowest Si excess. A discussion on the probable mechanism of emission is presented.

Research paper thumbnail of Photoluminescence enhancement through silicon implantation on SRO-LPCVD films

Materials Science and Engineering: B, 2010

Photoluminescence (PL) properties of thin and thick silicon-rich oxide (SRO) and silicon implante... more Photoluminescence (PL) properties of thin and thick silicon-rich oxide (SRO) and silicon implanted SRO (SI-SRO) films with different silicon excess fabricated by low pressure chemical vapor deposition (LPCVD) were studied. The effects of the annealing temperature and silicon implantation on the PL were also studied. Maximum luminescence intensity was observed with an annealing temperature of 1150 and 1100 • C for thin and thick SRO films, respectively. The PL intensity is strongly enhanced when SRO films are implanted with silicon, especially for thin SRO films. Thin SI-SRO films emit up to six times more than non-implanted films, meanwhile the PL in thick SI-SRO films is only improved less than two times. Therefore, thin SI-SRO films are an interesting alternative for applications such as the fabrication of efficient Si-nps based LEDs.