Daniele Barettin | Università degli studi Niccolò Cusano, telematica Roma (original) (raw)
Papers by Daniele Barettin
Advanced photonics research, May 18, 2022
Figure 3. Optical electric field distribution at different textured interfaces: a) rectangular ba... more Figure 3. Optical electric field distribution at different textured interfaces: a) rectangular back charge transporting layer, b) rectangular top charge transporting layer, c) moth-eye textured top contact with in respect to the according references in red wavelength range. (a) Reproduced with permission. [91]
Engineering Science and Technology, an International Journal, May 1, 2023
Proceedings of SPIE, Feb 19, 2014
ABSTRACT The development of epitaxial technology for the fabrication of quantum dot (QD) gain mat... more ABSTRACT The development of epitaxial technology for the fabrication of quantum dot (QD) gain material operating in the 1.55 μm wavelength range is a key requirement for the evolvement of telecommunication. High performance QD material demonstrated on GaAs only covers the wavelength region 1-1.35 μm. In order to extract the QD benefits for the longer telecommunication wavelength range the technology of QD fabrication should be developed for InP based materials. In our work, we take advantage of both QD fabrication methods Stranski-Krastanow (SK) and selective area growth (SAG) employing block copolymer lithography. Due to the lower lattice mismatch of InAs/InP compared to InAs/GaAs, InP based QDs have a larger diameter and are shallower compared to GaAs based dots. This shape causes low carrier localization and small energy level separation which leads to a high threshold current, high temperature dependence, and low laser quantum efficiency. Here, we demonstrate that with tailored growth conditions, which suppress surface migration of adatoms during the SK QD formation, much smaller base diameter (13.6nm versus 23nm) and an improved aspect ratio are achieved. In order to gain advantage of non-strain dependent QD formation, we have developed SAG, for which the growth occurs only in the nano-openings of a mask covering the wafer surface. In this case, a wide range of QD composition can be chosen. This method yields high purity material and provides significant freedom for reducing the aspect ratio of QDs with the possibility to approach an ideal QD shape.
Bulletin of The Russian Academy of Sciences: Physics, Dec 1, 2022
Nanomaterials
The main intent of this paper is to present an exhaustive description of the most relevant mathem... more The main intent of this paper is to present an exhaustive description of the most relevant mathematical models for the electromechanical properties of heterostructure quantum dots. Models are applied both to wurtzite and zincblende quantum dot due to the relevance they have shown for optoelectronic applications. In addition to a complete overview of the continuous and atomistic models for the electromechanical fields, analytical results will be presented for some relevant approximations, some of which are unpublished, such as models in cylindrical approximation or a cubic approximation for the transformation of a zincblende parametrization to a wurtzite one and vice versa. All analytical models will be supported by a wide range of numerical results, most of which are also compared with experimental measurements.
Materials
The synthesis of crystals with a high surface-to-volume ratio is essential for innovative, high-p... more The synthesis of crystals with a high surface-to-volume ratio is essential for innovative, high-performance electronic devices and sensors. The easiest way to achieve this in integrated devices with electronic circuits is through the synthesis of high-aspect-ratio nanowires aligned vertically to the substrate surface. Such surface structuring is widely employed for the fabrication of photoanodes for solar cells, either combined with semiconducting quantum dots or metal halide perovskites. In this review, we focus on wet chemistry recipes for the growth of vertically aligned nanowires and technologies for their surface functionalization with quantum dots, highlighting the procedures that yield the best results in photoconversion efficiencies on rigid and flexible substrates. We also discuss the effectiveness of their implementation. Among the three main materials used for the fabrication of nanowire-quantum dot solar cells, ZnO is the most promising, particularly due to its piezo-pho...
Lecture notes in electrical engineering, 2023
Nanomaterials
We present a study with a numerical model based on k→·p→, including electromechanical fields, to ... more We present a study with a numerical model based on k→·p→, including electromechanical fields, to evaluate the electromechanical and optoelectronic properties of single GaAs quantum dots embedded in direct band gap AlGaAs nanowires. The geometry and the dimensions of the quantum dots, in particular the thickness, are obtained from experimental data measured by our group. We also present a comparison between the experimental and numerically calculated spectra to support the validity of our model.
Nanomaterials
A possible solution for the realization of high-efficiency visible light-emitting diodes (LEDs) e... more A possible solution for the realization of high-efficiency visible light-emitting diodes (LEDs) exploits InGaN-quantum-dot-based active regions. However, the role of local composition fluctuations inside the quantum dots and their effect of the device characteristics have not yet been examined in sufficient detail. Here, we present numerical simulations of a quantum-dot structure restored from an experimental high-resolution transmission electron microscopy image. A single InGaN island with the size of ten nanometers and nonuniform indium content distribution is analyzed. A number of two- and three-dimensional models of the quantum dot are derived from the experimental image by a special numerical algorithm, which enables electromechanical, continuum k→·p→, and empirical tight-binding calculations, including emission spectra prediction. Effectiveness of continuous and atomistic approaches are compared, and the impact of InGaN composition fluctuations on the ground-state electron and...
Nanomaterials
A recent innovation in diamond technology has been the development of the “black diamond” (BD), a... more A recent innovation in diamond technology has been the development of the “black diamond” (BD), a material with very high optical absorption generated by processing the diamond surface with a femtosecond laser. In this work, we investigate the optical behavior of the BD samples to prove a near to zero dielectric permittivity in the high electric field condition, where the Frenkel-Poole (FP) effect takes place. Zero-epsilon materials (ENZ), which represent a singularity in optical materials, are expected to lead to remarkable developments in the fields of integrated photonic devices and optical interconnections. Such a result opens the route to the development of BD-based, novel, functional photonic devices.
Nanomaterials
We exploit the three-dimensional (3D) character of the strain field created around InGaN islands ... more We exploit the three-dimensional (3D) character of the strain field created around InGaN islands formed within the multilayer structures spaced by a less than 1-nm-thick GaN layer for the creation of spatially correlated electronically coupled quantum dots (QDs). The laterally inhomogeneous vertical out-diffusion of In atoms during growth interruption is the basic mechanism for the formation of InGaN islands within as-deposited 2D layers. An anisotropic 3D strain field created in the first layer is sufficient to justify the vertical correlation of the islands formed in the upper layers spaced by a sufficiently thin GaN layer. When the thickness of a GaN spacer exceeds 1 nm, QDs from different layers under the same growth conditions emit independently and in the same wavelength range. When extremely thin (less than 1 nm), a GaN spacer is formed solely by applying short GI, and a double wavelength emission in the blue and green spectral ranges evidences the electromechanical coupling....
2022 IEEE International Symposium on Medical Measurements and Applications (MeMeA)
2015 IEEE 15th International Conference on Nanotechnology (IEEE-NANO), 2015
We report on numerical simulations of GaAs/Al0.3Ga0.7As complex quantum dot/ring nanostructure. B... more We report on numerical simulations of GaAs/Al0.3Ga0.7As complex quantum dot/ring nanostructure. Both the empirical tight-binding (ETB) model with a sp3d5s*+spin-orbit parametrization and k.p model are used to study the electronic properties of the complex quantum system. Graphical processing units (GPUs) are employed to carry out the ETB calculation within a reasonable time frame for systems with varying quantum dot size. The goal of our investigation is to fine tune the electronic properties of the complex nanostructure via size tuning, in order to find lambda states (coupled states) that are localized in both the quantum dot and quantum ring.
Journal of Physics: Materials, 2021
Using an 8-band k ⋅ p model it is demonstrated through the combination of strain and piezoelectri... more Using an 8-band k ⋅ p model it is demonstrated through the combination of strain and piezoelectricity that increasing the InN quantum-well thickness of a GaN-InN-GaN device changes the InN material from a positive bandgap semiconductor to a topological insulator (negative bandgap). Moderate strain tuning of a four monolayer InN layer for a GaN-InN-GaN device reveals a giant (one order of magnitude) tuning of current–voltage characteristics. It is verified that piezoelectricity plays an important role in controlling electron transport through the InN layer.
Nanomaterials
Antireflection and light-trapping coatings are important parts of photovoltaic architectures, whi... more Antireflection and light-trapping coatings are important parts of photovoltaic architectures, which enable the reduction of parasitic optical losses, and therefore increase the power conversion efficiency (PCE). Here, we propose a novel approach to enhance the efficiency of perovskite solar cells using a light-trapping electrode (LTE) with non-reciprocal optical transmission, consisting of a perforated metal film covered with a densely packed array of nanospheres. Our LTE combines charge collection and light trapping, and it can replace classical transparent conducting oxides (TCOs) such as ITO or FTO, providing better optical transmission and conductivity. One of the most promising applications of our original LTE is the optimization of efficient bifacial perovskite solar cells. We demonstrate that with our LTE, the short-circuit current density and fill factor are improved for both front and back illumination of the solar cells. Thus, we observe an 11% improvement in the light abs...
Optical and Quantum Electronics
We present in this article the implementation of a cellular automaton to predict light emission f... more We present in this article the implementation of a cellular automaton to predict light emission from an InGaN/GaN quantum dot-based matrix. In particular, we determined the characteristic of the matrix in order to obtain white light in quantum-dot based LEDs. We created a cellular automaton that performs the requested task through a number of steps that increases linearly with the size of the matrix, thus ensuring a valid tool for large-sized quantum dot matrices.
Nanomaterials
Black diamond is an emerging material for solar applications. The femtosecond laser surface treat... more Black diamond is an emerging material for solar applications. The femtosecond laser surface treatment of pristine transparent diamond allows the solar absorptance to be increased to values greater than 90% from semi-transparency conditions. In addition, the defects introduced by fs-laser treatment strongly increase the diamond surface electrical conductivity and a very-low activation energy is observed at room temperature. In this work, the investigation of electronic transport mechanisms of a fs-laser nanotextured diamond surface is reported. The charge transport was studied down to cryogenic temperatures, in the 30–300 K range. The samples show an activation energy of a few tens of meV in the highest temperature interval and for T < 50 K, the activation energy diminishes to a few meV. Moreover, thanks to fast cycles of measurement, we noticed that the black-diamond samples also seem to show a behavior close to ferromagnetic materials, suggesting electron spin influence over the...
Abstract—We present a numerical model of quasi onedimensional and quasi zero-dimensional semicond... more Abstract—We present a numerical model of quasi onedimensional and quasi zero-dimensional semiconductor heterostructures strictly based on experimental structures of polyphorm cylindrical nanocolumns. I.
Advanced photonics research, May 18, 2022
Figure 3. Optical electric field distribution at different textured interfaces: a) rectangular ba... more Figure 3. Optical electric field distribution at different textured interfaces: a) rectangular back charge transporting layer, b) rectangular top charge transporting layer, c) moth-eye textured top contact with in respect to the according references in red wavelength range. (a) Reproduced with permission. [91]
Engineering Science and Technology, an International Journal, May 1, 2023
Proceedings of SPIE, Feb 19, 2014
ABSTRACT The development of epitaxial technology for the fabrication of quantum dot (QD) gain mat... more ABSTRACT The development of epitaxial technology for the fabrication of quantum dot (QD) gain material operating in the 1.55 μm wavelength range is a key requirement for the evolvement of telecommunication. High performance QD material demonstrated on GaAs only covers the wavelength region 1-1.35 μm. In order to extract the QD benefits for the longer telecommunication wavelength range the technology of QD fabrication should be developed for InP based materials. In our work, we take advantage of both QD fabrication methods Stranski-Krastanow (SK) and selective area growth (SAG) employing block copolymer lithography. Due to the lower lattice mismatch of InAs/InP compared to InAs/GaAs, InP based QDs have a larger diameter and are shallower compared to GaAs based dots. This shape causes low carrier localization and small energy level separation which leads to a high threshold current, high temperature dependence, and low laser quantum efficiency. Here, we demonstrate that with tailored growth conditions, which suppress surface migration of adatoms during the SK QD formation, much smaller base diameter (13.6nm versus 23nm) and an improved aspect ratio are achieved. In order to gain advantage of non-strain dependent QD formation, we have developed SAG, for which the growth occurs only in the nano-openings of a mask covering the wafer surface. In this case, a wide range of QD composition can be chosen. This method yields high purity material and provides significant freedom for reducing the aspect ratio of QDs with the possibility to approach an ideal QD shape.
Bulletin of The Russian Academy of Sciences: Physics, Dec 1, 2022
Nanomaterials
The main intent of this paper is to present an exhaustive description of the most relevant mathem... more The main intent of this paper is to present an exhaustive description of the most relevant mathematical models for the electromechanical properties of heterostructure quantum dots. Models are applied both to wurtzite and zincblende quantum dot due to the relevance they have shown for optoelectronic applications. In addition to a complete overview of the continuous and atomistic models for the electromechanical fields, analytical results will be presented for some relevant approximations, some of which are unpublished, such as models in cylindrical approximation or a cubic approximation for the transformation of a zincblende parametrization to a wurtzite one and vice versa. All analytical models will be supported by a wide range of numerical results, most of which are also compared with experimental measurements.
Materials
The synthesis of crystals with a high surface-to-volume ratio is essential for innovative, high-p... more The synthesis of crystals with a high surface-to-volume ratio is essential for innovative, high-performance electronic devices and sensors. The easiest way to achieve this in integrated devices with electronic circuits is through the synthesis of high-aspect-ratio nanowires aligned vertically to the substrate surface. Such surface structuring is widely employed for the fabrication of photoanodes for solar cells, either combined with semiconducting quantum dots or metal halide perovskites. In this review, we focus on wet chemistry recipes for the growth of vertically aligned nanowires and technologies for their surface functionalization with quantum dots, highlighting the procedures that yield the best results in photoconversion efficiencies on rigid and flexible substrates. We also discuss the effectiveness of their implementation. Among the three main materials used for the fabrication of nanowire-quantum dot solar cells, ZnO is the most promising, particularly due to its piezo-pho...
Lecture notes in electrical engineering, 2023
Nanomaterials
We present a study with a numerical model based on k→·p→, including electromechanical fields, to ... more We present a study with a numerical model based on k→·p→, including electromechanical fields, to evaluate the electromechanical and optoelectronic properties of single GaAs quantum dots embedded in direct band gap AlGaAs nanowires. The geometry and the dimensions of the quantum dots, in particular the thickness, are obtained from experimental data measured by our group. We also present a comparison between the experimental and numerically calculated spectra to support the validity of our model.
Nanomaterials
A possible solution for the realization of high-efficiency visible light-emitting diodes (LEDs) e... more A possible solution for the realization of high-efficiency visible light-emitting diodes (LEDs) exploits InGaN-quantum-dot-based active regions. However, the role of local composition fluctuations inside the quantum dots and their effect of the device characteristics have not yet been examined in sufficient detail. Here, we present numerical simulations of a quantum-dot structure restored from an experimental high-resolution transmission electron microscopy image. A single InGaN island with the size of ten nanometers and nonuniform indium content distribution is analyzed. A number of two- and three-dimensional models of the quantum dot are derived from the experimental image by a special numerical algorithm, which enables electromechanical, continuum k→·p→, and empirical tight-binding calculations, including emission spectra prediction. Effectiveness of continuous and atomistic approaches are compared, and the impact of InGaN composition fluctuations on the ground-state electron and...
Nanomaterials
A recent innovation in diamond technology has been the development of the “black diamond” (BD), a... more A recent innovation in diamond technology has been the development of the “black diamond” (BD), a material with very high optical absorption generated by processing the diamond surface with a femtosecond laser. In this work, we investigate the optical behavior of the BD samples to prove a near to zero dielectric permittivity in the high electric field condition, where the Frenkel-Poole (FP) effect takes place. Zero-epsilon materials (ENZ), which represent a singularity in optical materials, are expected to lead to remarkable developments in the fields of integrated photonic devices and optical interconnections. Such a result opens the route to the development of BD-based, novel, functional photonic devices.
Nanomaterials
We exploit the three-dimensional (3D) character of the strain field created around InGaN islands ... more We exploit the three-dimensional (3D) character of the strain field created around InGaN islands formed within the multilayer structures spaced by a less than 1-nm-thick GaN layer for the creation of spatially correlated electronically coupled quantum dots (QDs). The laterally inhomogeneous vertical out-diffusion of In atoms during growth interruption is the basic mechanism for the formation of InGaN islands within as-deposited 2D layers. An anisotropic 3D strain field created in the first layer is sufficient to justify the vertical correlation of the islands formed in the upper layers spaced by a sufficiently thin GaN layer. When the thickness of a GaN spacer exceeds 1 nm, QDs from different layers under the same growth conditions emit independently and in the same wavelength range. When extremely thin (less than 1 nm), a GaN spacer is formed solely by applying short GI, and a double wavelength emission in the blue and green spectral ranges evidences the electromechanical coupling....
2022 IEEE International Symposium on Medical Measurements and Applications (MeMeA)
2015 IEEE 15th International Conference on Nanotechnology (IEEE-NANO), 2015
We report on numerical simulations of GaAs/Al0.3Ga0.7As complex quantum dot/ring nanostructure. B... more We report on numerical simulations of GaAs/Al0.3Ga0.7As complex quantum dot/ring nanostructure. Both the empirical tight-binding (ETB) model with a sp3d5s*+spin-orbit parametrization and k.p model are used to study the electronic properties of the complex quantum system. Graphical processing units (GPUs) are employed to carry out the ETB calculation within a reasonable time frame for systems with varying quantum dot size. The goal of our investigation is to fine tune the electronic properties of the complex nanostructure via size tuning, in order to find lambda states (coupled states) that are localized in both the quantum dot and quantum ring.
Journal of Physics: Materials, 2021
Using an 8-band k ⋅ p model it is demonstrated through the combination of strain and piezoelectri... more Using an 8-band k ⋅ p model it is demonstrated through the combination of strain and piezoelectricity that increasing the InN quantum-well thickness of a GaN-InN-GaN device changes the InN material from a positive bandgap semiconductor to a topological insulator (negative bandgap). Moderate strain tuning of a four monolayer InN layer for a GaN-InN-GaN device reveals a giant (one order of magnitude) tuning of current–voltage characteristics. It is verified that piezoelectricity plays an important role in controlling electron transport through the InN layer.
Nanomaterials
Antireflection and light-trapping coatings are important parts of photovoltaic architectures, whi... more Antireflection and light-trapping coatings are important parts of photovoltaic architectures, which enable the reduction of parasitic optical losses, and therefore increase the power conversion efficiency (PCE). Here, we propose a novel approach to enhance the efficiency of perovskite solar cells using a light-trapping electrode (LTE) with non-reciprocal optical transmission, consisting of a perforated metal film covered with a densely packed array of nanospheres. Our LTE combines charge collection and light trapping, and it can replace classical transparent conducting oxides (TCOs) such as ITO or FTO, providing better optical transmission and conductivity. One of the most promising applications of our original LTE is the optimization of efficient bifacial perovskite solar cells. We demonstrate that with our LTE, the short-circuit current density and fill factor are improved for both front and back illumination of the solar cells. Thus, we observe an 11% improvement in the light abs...
Optical and Quantum Electronics
We present in this article the implementation of a cellular automaton to predict light emission f... more We present in this article the implementation of a cellular automaton to predict light emission from an InGaN/GaN quantum dot-based matrix. In particular, we determined the characteristic of the matrix in order to obtain white light in quantum-dot based LEDs. We created a cellular automaton that performs the requested task through a number of steps that increases linearly with the size of the matrix, thus ensuring a valid tool for large-sized quantum dot matrices.
Nanomaterials
Black diamond is an emerging material for solar applications. The femtosecond laser surface treat... more Black diamond is an emerging material for solar applications. The femtosecond laser surface treatment of pristine transparent diamond allows the solar absorptance to be increased to values greater than 90% from semi-transparency conditions. In addition, the defects introduced by fs-laser treatment strongly increase the diamond surface electrical conductivity and a very-low activation energy is observed at room temperature. In this work, the investigation of electronic transport mechanisms of a fs-laser nanotextured diamond surface is reported. The charge transport was studied down to cryogenic temperatures, in the 30–300 K range. The samples show an activation energy of a few tens of meV in the highest temperature interval and for T < 50 K, the activation energy diminishes to a few meV. Moreover, thanks to fast cycles of measurement, we noticed that the black-diamond samples also seem to show a behavior close to ferromagnetic materials, suggesting electron spin influence over the...
Abstract—We present a numerical model of quasi onedimensional and quasi zero-dimensional semicond... more Abstract—We present a numerical model of quasi onedimensional and quasi zero-dimensional semiconductor heterostructures strictly based on experimental structures of polyphorm cylindrical nanocolumns. I.