Rosa Chierchia - Academia.edu (original) (raw)

Papers by Rosa Chierchia

Philosophical Magazine B

The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) ... more The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) microcavities were formed on p ¡ -type-doped (6± 9 W cm) substrates with very narrow bandwidth (6 nm) and a good ratio of the peak to background emission, reaching at the same time a high emission quantum e ciency. Secondly light-emitting diodes (LEDs) based on n-type-doped Si/PS heterojunctions were studied. The improvement in the proposed LED structure with respect to the usual metal/PS LED is demonstrated. Anodic oxidation experiments show further improvements in the LED e ciency. Thirdly, SiO 2 / Si/SiO 2 quantum wells with room-temperature e cient light emission in the visible range were investigated. We report here the preparation and photoluminescence properties of thin SiO 2 /Si layers obtained by low-pressure chemical vapour-phase deposition and thermal oxidation processes. The growth technique is fully compatible with standard very-large-scale integration complementary metal± oxide± semiconductor technology.

Philosophical Magazine Part B, 2000

The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) ... more The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) microcavities were formed on p ¡ -type-doped (6± 9 W cm) substrates with very narrow bandwidth (6 nm) and a good ratio of the peak to background emission, reaching at the same time a high emission quantum e ciency. Secondly light-emitting diodes (LEDs) based on n-type-doped Si/PS heterojunctions were studied. The improvement in the proposed LED structure with respect to the usual metal/PS LED is demonstrated. Anodic oxidation experiments show further improvements in the LED e ciency. Thirdly, SiO 2 / Si/SiO 2 quantum wells with room-temperature e cient light emission in the visible range were investigated. We report here the preparation and photoluminescence properties of thin SiO 2 /Si layers obtained by low-pressure chemical vapour-phase deposition and thermal oxidation processes. The growth technique is fully compatible with standard very-large-scale integration complementary metal± oxide± semiconductor technology.

The most attracting way to fabricate high efficiency solar cells is the amorphous/crystalline sil... more The most attracting way to fabricate high efficiency solar cells is the amorphous/crystalline silicon technology, because of the high Voc obtainable as a consequence of excellent c-Si surface passivation offered by a-Si:H films. This passivation is obtained by saturation of silicon dangling bonds at c-Si/a-Si interface and can be influenced by the hydrogen inclusion within the a-Si:H layer. In this work we propose the use of hydrogen plasma treatments subsequently performed on the thin amorphous silicon layer deposited to passivate the c-Si surface. We compare the hydrogen effect on the interface with that of thermal annealing of the interface to identify how the hydrogen evolves inside the a-Si:H network modifying the defect density and the a-Si:H/c -Si interface. To monitor the hydrogen effect on the heterointerface we propose the use of surface photovoltage technique as a contact-less tool for the evaluation of the energetic distribution of the state density at amorphous/crystall...

MRS Proceedings, 2002

ABSTRACT The microstructural evolution of AlxGa1-xN films grown by metalorganic vapor phase epita... more ABSTRACT The microstructural evolution of AlxGa1-xN films grown by metalorganic vapor phase epitaxy on 6H-SiC (0001) was studied by means of X-ray diffraction, atomic force microscopy and transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy. A significant spatial variation of composition was found in 100 nm thick layers the nature of which could be traced back to the initial stage of film formation. Upon nucleation two phases are formed: a wetting layer and isolated islands of high and low aluminum content, respectively. The observed results are discussed in terms of strain and growth rates.

The optical properties of nonimaging 3D-CPC solar concentrators, irradiated by collimated beams, ... more The optical properties of nonimaging 3D-CPC solar concentrators, irradiated by collimated beams, have been investigated by using original simulation methods. These methods were not limited to investigate properties directly related to the practical application of the concentrators, but were also used to study any detailed aspect related to their transmission, reflection and absorption characteristics. We have investigated, therefore, besides to the flux transmitted to the receiver, also the flux back reflected and the flux absorbed on the internal wall of the concentrator. The main results of the simulations were: efficiency of transmission, reflection and absorption, average number of reflections on the internal wall of both transmitted and reflected rays, their angular divergence at the output and at the input of the concentrator, respectively, distribution of flux on the receiver and on the internal wall surface. The above mentioned theoretical investigations on 3D-CPC solar concentrators are aimed at improving the knowledge of their optical properties, expanding their application field and opening new perspectives to the methods of their characterization. The presented methods can be fruitfully applied to any other type of solar concentrator.

Semiconductors compound as Cu 2 SnS 3 (CTS) with cheap and more available elements are getting mo... more Semiconductors compound as Cu 2 SnS 3 (CTS) with cheap and more available elements are getting more and more interest. Its low bandgap makes it suitable as absorber in the long wavelength region in solar cell with heterojunction structure. In this work CTS thin films are grown by two-steps processes: precursor deposition by cosputtering of CuS and SnS, followed by a thermal treatment in sulphur atmosphere. A first optimization of this process allowed to make a CTS based solar cell exhibiting short circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF) of 29.7 mA/cm 2 , 0.219 V as well as a total-area power-conversion efficiency of 2.37%. Furthermore the External Quantum Efficiency (EQE) curve at wavelength higher than 1200 nm has values higher than 10%.

The Journal of Physical Chemistry C, 2007

The relation between the electrical, chemical, and morphological properties of indium-tin oxide (... more The relation between the electrical, chemical, and morphological properties of indium-tin oxide (ITO) thin films and organic light-emitting diode (OLED) performance is studied. We report on chemical (HCl, piranha solutions), thermal (vacuum annealing), physical (oxygen plasma, UV ozone), and combined treatments on ITO layers. The effects of these different treatments have been studied using the four-point probe resistivity measurement method, contact angle measurement, X-ray diffraction, surface profilometry, and UV-vis-IR transmittance. Double-layer OLEDs with treated ITO as the anode and poly(9,9-dihexyl-9H-fluorene-2,7diyl) and 8-hydroxyquinoline aluminum salt as the hole transporter and emitting material, respectively, have been realized. The electrical and optical properties of OLEDs have been extensively investigated, and it is shown that UV ozone-HCl combined treatment yields the highest hole injection efficiency and luminance and the lowest drive voltage. For each OLED with treated ITO, the anode potential barrier height decrease is estimated using Fowler-Nordheim and Schottky-Richardson modeling of the electrical conduction.

Energy Procedia, 2014

High efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon techn... more High efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon technology, taking advantage of the high V oc that occurs as a consequence of excellent c-Si surface passivation provided by a-Si:H films. Improvements of the interface quality can be obtained using post deposition treatments such as hydrogen plasma and thermal annealing. We propose the use of surface photovoltage technique, as a contact-less tool to evaluate the energetic distribution of the state density at amorphous/crystalline silicon interface, and FTIR spectroscopy of the same samples to appreciate the evolution of Si-H and Si-H 2 bonds. This approach leads to interesting applications for monitoring and improving the interface electronic quality, which is extremely susceptible to the different treatments adopted. We found that thermal annealing produces a metastable state which goes back to the initial state after just 48 hours, while the effect of hydrogen plasma post-treatment results more stable. Moreover H 2 plasma reduces the defect density of one order of magnitude with respect to thermal annealing and keeps it constant also after one month. The hydrogen plasma is able to reduce the defect density but at the same time increases the surface charge within the a-Si:H film due to the H + ions accumulated during the plasma exposure, leading to a more stable configuration.

Macromolecular Symposia, 2007

studies on the influence of chemical and physical treatments on the properties of indium-tin oxid... more studies on the influence of chemical and physical treatments on the properties of indium-tin oxide (ITO) thin films are reported. The ITO films are utilized as transparent anodes of organic light-emitting diodes (OLEDs) incorporating poly(9,9-dihexyl-9H-fluorene-2,7-diyl) (PF6) as the hole transporter material and 8-hydroxyquinoline aluminum salt (Alq3) as emitter material. Chemical (HCl, piranha solutions), thermal (vacuum annealing), physical treatments (oxygen plasma, UV ozone) and combined treatments are studied. First, ITO layers with different treatments are characterized by using four point probe method, contact angle measurement, X-Ray diffraction (XRD), surface profilometer, scanning electron microscopy (SEM), UV-Vis-IR transmittance. Later, electrical and optical properties of OLEDs with treated ITO as anode are extensively investigated.

Energy Procedia, 2011

Cu 2 ZnSnS 4 (CZTS) is a promising material for the production of thin film photovoltaic modules.... more Cu 2 ZnSnS 4 (CZTS) is a promising material for the production of thin film photovoltaic modules. In this paper we report on the fabrication and characterization of ZnO/CdS/CZTS/Mo solar cells. The CZTS absorber was grown by sulfurization of a precursor composed of a multilayer of ZnS, Sn and Cu. The CZTS structural, compositional and electronic properties were investigated by XRD, SEM-EDS, Raman spectroscopy and conductivity and mobility measurements. Solar cells with the structure ZnO/CdS/CZTS/Mo were produced and fully characterized. The problems connected to the back contact are investigated and discussed.

2014 IEEE 40th Photovoltaic Specialist Conference (PVSC), 2014

Energy Procedia, 2014

Al doped zinc oxide (ZnO:Al) is a transparent and conductive oxide used as contact and antireflec... more Al doped zinc oxide (ZnO:Al) is a transparent and conductive oxide used as contact and antireflection layer in solar cell based on Si or chalcogenide. Generally it is grown by magnetron sputtering but the resistivity of our films grown with this technique are still in the order of 10 -3 cm for layers grown at the temperatures used to produce the solar cells. The doping property of Hydrogen for Al:ZnO grown with two different sputtering techniques, DC magnetron sputtering and Pulsed magnetron sputtering at different growth parameters have been studied and the sample characterized optically, electrically and structurally. The best resistivity is 6.7*10 -4 cm was obtained using Pulsed magnetron sputtering.

physica status solidi (c), 2003

The application of SiN interlayers in GaN-based structures for the annihilation of threading disl... more The application of SiN interlayers in GaN-based structures for the annihilation of threading dislocations captivates by its simplicity and the possibility to use it . However, since the metalorganic vapor phase epitaxy (MOVPE) of the group-III nitrides happens in a hydrogen-containing atmosphere, the surface decomposes during the SiN deposition. This work addresses the impact of the SiN growth with respect to temperature and surface dose. In particular, a quantitative analysis of the surface coverage is presented and the successive overgrowth with GaN is discussed in view of threading dislocation density and island growth mode.

physica status solidi (b), 2001

High-resolution X-ray diffraction has been used to analyze GaN epilayers with varying coalescence... more High-resolution X-ray diffraction has been used to analyze GaN epilayers with varying coalescence thickness which were grown by MOVPE on (0001) oriented sapphire. The decrease of the density of edge type threading dislocations with increasing coalescence thickness causes a marked difference in the mosaicity of the samples. As the defects form along the grain boundaries, this corresponds to an increase in lateral coherence length with increasing coalescence thickness. The lateral coherence length has been obtained from simulations of reciprocal lattice points of off-axis Bragg reflections, measured in asymmetric diffraction geometry.

Journal of Physics D: Applied Physics, 2001

GaN(0001) epitaxial layers were grown by molecular beam epitaxy on a few-nanometres thick low-tem... more GaN(0001) epitaxial layers were grown by molecular beam epitaxy on a few-nanometres thick low-temperature GaN nucleation layers on c-plane sapphire. Despite extremely high densities of extended defects, the layers show a narrow (002) x-ray diffraction peak, superimposed by broad diffuse scattering. Triple-axis transverse and radial scans were measured for (00l) reflections of different orders and for various GaN layer thicknesses. The results can be described by an interfacial displacement-difference correlation function. Its microscopic origin is assigned to either inversion domain boundaries or edge-type threading dislocations in the GaN layers, in agreement with findings of transmission electron microscopy. These defects are associated with an only weak rotational disorder perpendicular to the growth plane as proven by the x-ray scattering characteristics.

Journal of Physics D: Applied Physics, 2013

The Valence Band Offset (VBO) at the interface CdS/Cu 2 ZnSnS 4 has been investigated by X-Ray Ph... more The Valence Band Offset (VBO) at the interface CdS/Cu 2 ZnSnS 4 has been investigated by X-Ray Photoelectron Spectroscopy (XPS). The VBO has been measured by two different procedures: an indirect method involving the measurements of the core levels together with the XPS bulk valence band spectra and a direct method involving the analysis of XPS valence band spectra at the interface. The indirect method resulted in a VBO value of (−1.20 ± 0.14) eV while the direct method returned a similar value of (−1.24±0.06) eV but affected by a lower uncertainty. The conduction band offset (CBO) was calculated from the measured VBO values. These two measured values of the VBO allowed to calculate the conduction band offset (CBO), giving (−0.30 ± 0.14) eV and (−0.34 ± 0.06) eV respectively. These values show that the CBO has a cliff-like behavior which could be one of the reasons for the Voc limitation in the CdS/CZTS solar cells.

Journal of Applied Physics, 2003

The mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exh... more The mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exhibiting different grain diameters is studied using high-resolution x-ray diffraction. The coherence lengths, the tilt, and the twist of the mosaic structure are determined utilizing data taken in different x-ray scattering geometries. The results of different models, which were applied, are then compared and discussed. The dislocation densities, obtained from the x-ray data, are compared with the results of plan-view transmission electron microscopy and atomic force microscopy.

Journal of Alloys and Compounds, 2014

The considerable spread of Cu 2 ZnSnS 4 (CZTS) optical properties reported in the literature is d... more The considerable spread of Cu 2 ZnSnS 4 (CZTS) optical properties reported in the literature is discussed in terms of material stoichiometry. To this purpose, kesterite thin films were prepared by sulfurization of multilayered precursors of ZnS, Cu and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy were used for structural and compositional analysis. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric and Photothermal Deflection Spectroscopy (PDS) measurements to assess the absorption coefficient of samples with different compositions. The PDS data show an increase of the sub-band absorption as the Sn content decreases.

Philosophical Magazine B

The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) ... more The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) microcavities were formed on p ¡ -type-doped (6± 9 W cm) substrates with very narrow bandwidth (6 nm) and a good ratio of the peak to background emission, reaching at the same time a high emission quantum e ciency. Secondly light-emitting diodes (LEDs) based on n-type-doped Si/PS heterojunctions were studied. The improvement in the proposed LED structure with respect to the usual metal/PS LED is demonstrated. Anodic oxidation experiments show further improvements in the LED e ciency. Thirdly, SiO 2 / Si/SiO 2 quantum wells with room-temperature e cient light emission in the visible range were investigated. We report here the preparation and photoluminescence properties of thin SiO 2 /Si layers obtained by low-pressure chemical vapour-phase deposition and thermal oxidation processes. The growth technique is fully compatible with standard very-large-scale integration complementary metal± oxide± semiconductor technology.

Philosophical Magazine Part B, 2000

The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) ... more The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) microcavities were formed on p ¡ -type-doped (6± 9 W cm) substrates with very narrow bandwidth (6 nm) and a good ratio of the peak to background emission, reaching at the same time a high emission quantum e ciency. Secondly light-emitting diodes (LEDs) based on n-type-doped Si/PS heterojunctions were studied. The improvement in the proposed LED structure with respect to the usual metal/PS LED is demonstrated. Anodic oxidation experiments show further improvements in the LED e ciency. Thirdly, SiO 2 / Si/SiO 2 quantum wells with room-temperature e cient light emission in the visible range were investigated. We report here the preparation and photoluminescence properties of thin SiO 2 /Si layers obtained by low-pressure chemical vapour-phase deposition and thermal oxidation processes. The growth technique is fully compatible with standard very-large-scale integration complementary metal± oxide± semiconductor technology.

The most attracting way to fabricate high efficiency solar cells is the amorphous/crystalline sil... more The most attracting way to fabricate high efficiency solar cells is the amorphous/crystalline silicon technology, because of the high Voc obtainable as a consequence of excellent c-Si surface passivation offered by a-Si:H films. This passivation is obtained by saturation of silicon dangling bonds at c-Si/a-Si interface and can be influenced by the hydrogen inclusion within the a-Si:H layer. In this work we propose the use of hydrogen plasma treatments subsequently performed on the thin amorphous silicon layer deposited to passivate the c-Si surface. We compare the hydrogen effect on the interface with that of thermal annealing of the interface to identify how the hydrogen evolves inside the a-Si:H network modifying the defect density and the a-Si:H/c -Si interface. To monitor the hydrogen effect on the heterointerface we propose the use of surface photovoltage technique as a contact-less tool for the evaluation of the energetic distribution of the state density at amorphous/crystall...

MRS Proceedings, 2002

ABSTRACT The microstructural evolution of AlxGa1-xN films grown by metalorganic vapor phase epita... more ABSTRACT The microstructural evolution of AlxGa1-xN films grown by metalorganic vapor phase epitaxy on 6H-SiC (0001) was studied by means of X-ray diffraction, atomic force microscopy and transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy. A significant spatial variation of composition was found in 100 nm thick layers the nature of which could be traced back to the initial stage of film formation. Upon nucleation two phases are formed: a wetting layer and isolated islands of high and low aluminum content, respectively. The observed results are discussed in terms of strain and growth rates.

The optical properties of nonimaging 3D-CPC solar concentrators, irradiated by collimated beams, ... more The optical properties of nonimaging 3D-CPC solar concentrators, irradiated by collimated beams, have been investigated by using original simulation methods. These methods were not limited to investigate properties directly related to the practical application of the concentrators, but were also used to study any detailed aspect related to their transmission, reflection and absorption characteristics. We have investigated, therefore, besides to the flux transmitted to the receiver, also the flux back reflected and the flux absorbed on the internal wall of the concentrator. The main results of the simulations were: efficiency of transmission, reflection and absorption, average number of reflections on the internal wall of both transmitted and reflected rays, their angular divergence at the output and at the input of the concentrator, respectively, distribution of flux on the receiver and on the internal wall surface. The above mentioned theoretical investigations on 3D-CPC solar concentrators are aimed at improving the knowledge of their optical properties, expanding their application field and opening new perspectives to the methods of their characterization. The presented methods can be fruitfully applied to any other type of solar concentrator.

Semiconductors compound as Cu 2 SnS 3 (CTS) with cheap and more available elements are getting mo... more Semiconductors compound as Cu 2 SnS 3 (CTS) with cheap and more available elements are getting more and more interest. Its low bandgap makes it suitable as absorber in the long wavelength region in solar cell with heterojunction structure. In this work CTS thin films are grown by two-steps processes: precursor deposition by cosputtering of CuS and SnS, followed by a thermal treatment in sulphur atmosphere. A first optimization of this process allowed to make a CTS based solar cell exhibiting short circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF) of 29.7 mA/cm 2 , 0.219 V as well as a total-area power-conversion efficiency of 2.37%. Furthermore the External Quantum Efficiency (EQE) curve at wavelength higher than 1200 nm has values higher than 10%.

The Journal of Physical Chemistry C, 2007

The relation between the electrical, chemical, and morphological properties of indium-tin oxide (... more The relation between the electrical, chemical, and morphological properties of indium-tin oxide (ITO) thin films and organic light-emitting diode (OLED) performance is studied. We report on chemical (HCl, piranha solutions), thermal (vacuum annealing), physical (oxygen plasma, UV ozone), and combined treatments on ITO layers. The effects of these different treatments have been studied using the four-point probe resistivity measurement method, contact angle measurement, X-ray diffraction, surface profilometry, and UV-vis-IR transmittance. Double-layer OLEDs with treated ITO as the anode and poly(9,9-dihexyl-9H-fluorene-2,7diyl) and 8-hydroxyquinoline aluminum salt as the hole transporter and emitting material, respectively, have been realized. The electrical and optical properties of OLEDs have been extensively investigated, and it is shown that UV ozone-HCl combined treatment yields the highest hole injection efficiency and luminance and the lowest drive voltage. For each OLED with treated ITO, the anode potential barrier height decrease is estimated using Fowler-Nordheim and Schottky-Richardson modeling of the electrical conduction.

Energy Procedia, 2014

High efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon techn... more High efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon technology, taking advantage of the high V oc that occurs as a consequence of excellent c-Si surface passivation provided by a-Si:H films. Improvements of the interface quality can be obtained using post deposition treatments such as hydrogen plasma and thermal annealing. We propose the use of surface photovoltage technique, as a contact-less tool to evaluate the energetic distribution of the state density at amorphous/crystalline silicon interface, and FTIR spectroscopy of the same samples to appreciate the evolution of Si-H and Si-H 2 bonds. This approach leads to interesting applications for monitoring and improving the interface electronic quality, which is extremely susceptible to the different treatments adopted. We found that thermal annealing produces a metastable state which goes back to the initial state after just 48 hours, while the effect of hydrogen plasma post-treatment results more stable. Moreover H 2 plasma reduces the defect density of one order of magnitude with respect to thermal annealing and keeps it constant also after one month. The hydrogen plasma is able to reduce the defect density but at the same time increases the surface charge within the a-Si:H film due to the H + ions accumulated during the plasma exposure, leading to a more stable configuration.

Macromolecular Symposia, 2007

studies on the influence of chemical and physical treatments on the properties of indium-tin oxid... more studies on the influence of chemical and physical treatments on the properties of indium-tin oxide (ITO) thin films are reported. The ITO films are utilized as transparent anodes of organic light-emitting diodes (OLEDs) incorporating poly(9,9-dihexyl-9H-fluorene-2,7-diyl) (PF6) as the hole transporter material and 8-hydroxyquinoline aluminum salt (Alq3) as emitter material. Chemical (HCl, piranha solutions), thermal (vacuum annealing), physical treatments (oxygen plasma, UV ozone) and combined treatments are studied. First, ITO layers with different treatments are characterized by using four point probe method, contact angle measurement, X-Ray diffraction (XRD), surface profilometer, scanning electron microscopy (SEM), UV-Vis-IR transmittance. Later, electrical and optical properties of OLEDs with treated ITO as anode are extensively investigated.

Energy Procedia, 2011

Cu 2 ZnSnS 4 (CZTS) is a promising material for the production of thin film photovoltaic modules.... more Cu 2 ZnSnS 4 (CZTS) is a promising material for the production of thin film photovoltaic modules. In this paper we report on the fabrication and characterization of ZnO/CdS/CZTS/Mo solar cells. The CZTS absorber was grown by sulfurization of a precursor composed of a multilayer of ZnS, Sn and Cu. The CZTS structural, compositional and electronic properties were investigated by XRD, SEM-EDS, Raman spectroscopy and conductivity and mobility measurements. Solar cells with the structure ZnO/CdS/CZTS/Mo were produced and fully characterized. The problems connected to the back contact are investigated and discussed.

2014 IEEE 40th Photovoltaic Specialist Conference (PVSC), 2014

Energy Procedia, 2014

Al doped zinc oxide (ZnO:Al) is a transparent and conductive oxide used as contact and antireflec... more Al doped zinc oxide (ZnO:Al) is a transparent and conductive oxide used as contact and antireflection layer in solar cell based on Si or chalcogenide. Generally it is grown by magnetron sputtering but the resistivity of our films grown with this technique are still in the order of 10 -3 cm for layers grown at the temperatures used to produce the solar cells. The doping property of Hydrogen for Al:ZnO grown with two different sputtering techniques, DC magnetron sputtering and Pulsed magnetron sputtering at different growth parameters have been studied and the sample characterized optically, electrically and structurally. The best resistivity is 6.7*10 -4 cm was obtained using Pulsed magnetron sputtering.

physica status solidi (c), 2003

The application of SiN interlayers in GaN-based structures for the annihilation of threading disl... more The application of SiN interlayers in GaN-based structures for the annihilation of threading dislocations captivates by its simplicity and the possibility to use it . However, since the metalorganic vapor phase epitaxy (MOVPE) of the group-III nitrides happens in a hydrogen-containing atmosphere, the surface decomposes during the SiN deposition. This work addresses the impact of the SiN growth with respect to temperature and surface dose. In particular, a quantitative analysis of the surface coverage is presented and the successive overgrowth with GaN is discussed in view of threading dislocation density and island growth mode.

physica status solidi (b), 2001

High-resolution X-ray diffraction has been used to analyze GaN epilayers with varying coalescence... more High-resolution X-ray diffraction has been used to analyze GaN epilayers with varying coalescence thickness which were grown by MOVPE on (0001) oriented sapphire. The decrease of the density of edge type threading dislocations with increasing coalescence thickness causes a marked difference in the mosaicity of the samples. As the defects form along the grain boundaries, this corresponds to an increase in lateral coherence length with increasing coalescence thickness. The lateral coherence length has been obtained from simulations of reciprocal lattice points of off-axis Bragg reflections, measured in asymmetric diffraction geometry.

Journal of Physics D: Applied Physics, 2001

GaN(0001) epitaxial layers were grown by molecular beam epitaxy on a few-nanometres thick low-tem... more GaN(0001) epitaxial layers were grown by molecular beam epitaxy on a few-nanometres thick low-temperature GaN nucleation layers on c-plane sapphire. Despite extremely high densities of extended defects, the layers show a narrow (002) x-ray diffraction peak, superimposed by broad diffuse scattering. Triple-axis transverse and radial scans were measured for (00l) reflections of different orders and for various GaN layer thicknesses. The results can be described by an interfacial displacement-difference correlation function. Its microscopic origin is assigned to either inversion domain boundaries or edge-type threading dislocations in the GaN layers, in agreement with findings of transmission electron microscopy. These defects are associated with an only weak rotational disorder perpendicular to the growth plane as proven by the x-ray scattering characteristics.

Journal of Physics D: Applied Physics, 2013

The Valence Band Offset (VBO) at the interface CdS/Cu 2 ZnSnS 4 has been investigated by X-Ray Ph... more The Valence Band Offset (VBO) at the interface CdS/Cu 2 ZnSnS 4 has been investigated by X-Ray Photoelectron Spectroscopy (XPS). The VBO has been measured by two different procedures: an indirect method involving the measurements of the core levels together with the XPS bulk valence band spectra and a direct method involving the analysis of XPS valence band spectra at the interface. The indirect method resulted in a VBO value of (−1.20 ± 0.14) eV while the direct method returned a similar value of (−1.24±0.06) eV but affected by a lower uncertainty. The conduction band offset (CBO) was calculated from the measured VBO values. These two measured values of the VBO allowed to calculate the conduction band offset (CBO), giving (−0.30 ± 0.14) eV and (−0.34 ± 0.06) eV respectively. These values show that the CBO has a cliff-like behavior which could be one of the reasons for the Voc limitation in the CdS/CZTS solar cells.

Journal of Applied Physics, 2003

The mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exh... more The mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exhibiting different grain diameters is studied using high-resolution x-ray diffraction. The coherence lengths, the tilt, and the twist of the mosaic structure are determined utilizing data taken in different x-ray scattering geometries. The results of different models, which were applied, are then compared and discussed. The dislocation densities, obtained from the x-ray data, are compared with the results of plan-view transmission electron microscopy and atomic force microscopy.

Journal of Alloys and Compounds, 2014

The considerable spread of Cu 2 ZnSnS 4 (CZTS) optical properties reported in the literature is d... more The considerable spread of Cu 2 ZnSnS 4 (CZTS) optical properties reported in the literature is discussed in terms of material stoichiometry. To this purpose, kesterite thin films were prepared by sulfurization of multilayered precursors of ZnS, Cu and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy were used for structural and compositional analysis. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric and Photothermal Deflection Spectroscopy (PDS) measurements to assess the absorption coefficient of samples with different compositions. The PDS data show an increase of the sub-band absorption as the Sn content decreases.

Responsabile del Progetto: Paola Delli Veneri, ENEA Si ringraziano la dott. Amelia Montone e il d... more Responsabile del Progetto: Paola Delli Veneri, ENEA Si ringraziano la dott. Amelia Montone e il dott. Luciano Pilloni per la preziosa collaborazione nelle misure SEM ed EDX usate per la caratterizzazione morfologica e composizionale dei campioni di CZTS.