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Papers by Antonio Ferreira da Silva

physica status solidi (b), 2019

The inversion or sign change of the electron g‐factor anisotropy in thin‐layer semiconductor nano... more The inversion or sign change of the electron g‐factor anisotropy in thin‐layer semiconductor nanostructures is investigated theoretically and gauged for InGaAs asymmetric single and double quantum wells (QWs). The g‐factor anisotropy in these 2D nanostructures is given by the difference between the longitudinal and transverse components; it is a fine sensor of the confining potential and in InGaAs structures it is determined by the Rashba spin–orbit coupling. In the presence of structure inversion asymmetry (SIA) the g‐factor anisotropy is expected to invert at a critical well width. This effect can be useful technologically and is here analyzed in detail with InGaAs/InP asymmetric multi‐layer structures. The g‐factor anisotropy in these structures is calculated in a fine grid around the inversion point, using 8‐band kp Kane model based envelope function theory for the nanostructure, and perturbation theory for the calculation of the effective g factor. It is shown that the anisotro...

ITEGAM- Journal of Engineering and Technology for Industrial Applications (ITEGAM-JETIA), 2018

Surface Science, 1983

ABSTRACT The density of states for electrons bound to Na+ impurities inside the inversion layer a... more ABSTRACT The density of states for electrons bound to Na+ impurities inside the inversion layer at the semiconductor-insulator interface of an MOS structure is calculated as a function of impurity concentration. The impurity potential is considered unscreened and the electrical quantum limit is assumed. A simple one-electron Hamiltonian is used and the disorder is treated through a cluster calculation. It is shown that the impurity band has a considerable bandwidth for impurity concentrations in a range of the experimental regime (this result agrees with the experimental findings of Hartstein and Fowler), and that the upper Hubbard band stands well above the lower band at very low concentration (in rough agreement with recent calculation done by Phelps and Bajaj on D− state).

Superlattices and Microstructures, 1993

Superlattices and Microstructures, 1994

Solid State Communications, 1995

Solid State Communications, 1990

ABSTRACT

Modern Physics Letters B, 1992

The electric susceptibility due to interacting donor-pair molecules are presented for a random di... more The electric susceptibility due to interacting donor-pair molecules are presented for a random distribution of uncompensated phosphorus-doped silicon at T=0 K. The results yield a critical exponent and susceptibility enhancement observed in optical measurements.

Modern Physics Letters B, 1992

Quasi-one-dimensional channels have already been fabricated by holographic lithography on semicon... more Quasi-one-dimensional channels have already been fabricated by holographic lithography on semiconductor heterostructures. We study the formation of an impurity band for shallow donors located inside the channels assuming they have been created by applying a modulated gate voltage in a quantum well of AlxGa1−xAs−GaAs. We calculate the changes in the impurity density of states as a function of the gate voltage. It is shown that the increase of the applied gate voltage leads to higher binding energy and larger impurity bandwidth.

Journal of Physics: Condensed Matter, 1989

ABSTRACT Analytical calculations are made for a two-dimensional (2D) disordered system in order t... more ABSTRACT Analytical calculations are made for a two-dimensional (2D) disordered system in order to obtain the impurity density of states. It is shown that the impurity band is roughly symmetric and has no long low-energy tail, contrary to a three-dimensional system. The results are in agreement with the previous numerical calculations by Ferreira da Silva and Fabbri (1984) and are compared with other 2D models.

Journal of Non-Crystalline Solids, 1985

ABSTRACT A recent one-band model for impurity states in n-type many-valley semiconductor has been... more ABSTRACT A recent one-band model for impurity states in n-type many-valley semiconductor has been extended by self-consistent many-body and unrestricted Hartree-Fock approaches. The formulations are presented in order to discuss the shallow donor states in semiconductors. The impurity band splits into two Hubbard bands, presenting different aspects of the impurity states when the many-valley effects of the host conduction band are considered. These effects turn out to be essential for a better interpretation of the theoretical and experimental results. The results agree with some theoretical calculations and experimental findings.

Zinc Oxide (ZnO) and Silicon Carbide (SiC) are prominent materials with large applicability such ... more Zinc Oxide (ZnO) and Silicon Carbide (SiC) are prominent materials with large applicability such as optoelectronic nanodevices and for instance ultraviolet detectors. There is lack of important information about optical transitions beyond the indirect band gap energy (BGE) of 4H-SiC and even more for ZnO direct BGE grown on the former material. Using vapor-liquid-solid and the aqueous chemical growth methods we have grown ZnO nanorods on different substrates, such as quartz, n-and ptype porous silicon, and n-type 4H-SiC. Scanning electron microscopy (SEM) was employed to compare sample morphologies. The absorption was calculated employing a projector augmented wave (PAW) method. The measured absorption of ZnO nanorods, on different substrates, is lower than that observed for ZnO films on quartz substrate, in the low energy spectral range. It is observed a strong effect of 4H-SiC substrates on ZnO nanorod properties. Experiment and theory show a good agreement when the shape of the optical absorption is considered for both materials.

Journal of Applied Physics, 1996

We investigate the electrical properties of Bi-doped Si samples, prepared by ion implantation, in... more We investigate the electrical properties of Bi-doped Si samples, prepared by ion implantation, in a range of concentrations around and above the metal–nonmetal transition. Comparison between experimental and theoretical values of the resistivity brought out that in these samples a similar behavior is observed as for other n-doped Si, thus confirming the results obtained in the same range of impurity concentration, i.e., ρ(Sb)≤ρ(P)≤ρ(As)≤ρ(Bi).

Physical Review B - Condensed Matter and Materials Physics, 2000

The band-gap shift of the heavily single and double-donor doped systems Si:Bi and Si:P,Bi, prepar... more The band-gap shift of the heavily single and double-donor doped systems Si:Bi and Si:P,Bi, prepared by ion implantation, was investigated theoretically and experimentally at room temperature. The calculations were carried out within a framework of the random-phase approximation and the temperature and different manybody effects were taken into account. The experimental data were obtained with photoconductivity measurements. Theoretical and experimental results fall closely together in a wide range of donor concentration.

The optical absorption and the dielectric functions of PbI2 and Sb x Bi 1-x I 3 have been investi... more The optical absorption and the dielectric functions of PbI2 and Sb x Bi 1-x I 3 have been investigated experimentally by means of absorption measurements and spectroscopic ellipsometry respectively, and theoretically by a full-potential linear muffin-tin-orbital method. These materials have been recognized as very promising detector materials with large technological applicabilities. The calculated band-gap energies, optical absorption and the dielectric functions were found to be in a very good agreement with the experimental results. The electron-energy-loss functions are also obtained for both experiment and theory for comparison. The band-gap energy as a function of temperature, for PbI 2 has also been measured by optical absorption. The temperature dependence has been fitted by a new relation, and a discussion of this fitting is given.

Journal of Crystal Growth, 2014

Biomater. Sci., 2014

This communication describes a general method for templating fungal filaments with gold nanoparti... more This communication describes a general method for templating fungal filaments with gold nanoparticles that results in a gold replica of filaments after calcination of the biological template.

physica status solidi (b), 2019

The inversion or sign change of the electron g‐factor anisotropy in thin‐layer semiconductor nano... more The inversion or sign change of the electron g‐factor anisotropy in thin‐layer semiconductor nanostructures is investigated theoretically and gauged for InGaAs asymmetric single and double quantum wells (QWs). The g‐factor anisotropy in these 2D nanostructures is given by the difference between the longitudinal and transverse components; it is a fine sensor of the confining potential and in InGaAs structures it is determined by the Rashba spin–orbit coupling. In the presence of structure inversion asymmetry (SIA) the g‐factor anisotropy is expected to invert at a critical well width. This effect can be useful technologically and is here analyzed in detail with InGaAs/InP asymmetric multi‐layer structures. The g‐factor anisotropy in these structures is calculated in a fine grid around the inversion point, using 8‐band kp Kane model based envelope function theory for the nanostructure, and perturbation theory for the calculation of the effective g factor. It is shown that the anisotro...

ITEGAM- Journal of Engineering and Technology for Industrial Applications (ITEGAM-JETIA), 2018

Surface Science, 1983

ABSTRACT The density of states for electrons bound to Na+ impurities inside the inversion layer a... more ABSTRACT The density of states for electrons bound to Na+ impurities inside the inversion layer at the semiconductor-insulator interface of an MOS structure is calculated as a function of impurity concentration. The impurity potential is considered unscreened and the electrical quantum limit is assumed. A simple one-electron Hamiltonian is used and the disorder is treated through a cluster calculation. It is shown that the impurity band has a considerable bandwidth for impurity concentrations in a range of the experimental regime (this result agrees with the experimental findings of Hartstein and Fowler), and that the upper Hubbard band stands well above the lower band at very low concentration (in rough agreement with recent calculation done by Phelps and Bajaj on D− state).

Superlattices and Microstructures, 1993

Superlattices and Microstructures, 1994

Solid State Communications, 1995

Solid State Communications, 1990

ABSTRACT

Modern Physics Letters B, 1992

The electric susceptibility due to interacting donor-pair molecules are presented for a random di... more The electric susceptibility due to interacting donor-pair molecules are presented for a random distribution of uncompensated phosphorus-doped silicon at T=0 K. The results yield a critical exponent and susceptibility enhancement observed in optical measurements.

Modern Physics Letters B, 1992

Quasi-one-dimensional channels have already been fabricated by holographic lithography on semicon... more Quasi-one-dimensional channels have already been fabricated by holographic lithography on semiconductor heterostructures. We study the formation of an impurity band for shallow donors located inside the channels assuming they have been created by applying a modulated gate voltage in a quantum well of AlxGa1−xAs−GaAs. We calculate the changes in the impurity density of states as a function of the gate voltage. It is shown that the increase of the applied gate voltage leads to higher binding energy and larger impurity bandwidth.

Journal of Physics: Condensed Matter, 1989

ABSTRACT Analytical calculations are made for a two-dimensional (2D) disordered system in order t... more ABSTRACT Analytical calculations are made for a two-dimensional (2D) disordered system in order to obtain the impurity density of states. It is shown that the impurity band is roughly symmetric and has no long low-energy tail, contrary to a three-dimensional system. The results are in agreement with the previous numerical calculations by Ferreira da Silva and Fabbri (1984) and are compared with other 2D models.

Journal of Non-Crystalline Solids, 1985

ABSTRACT A recent one-band model for impurity states in n-type many-valley semiconductor has been... more ABSTRACT A recent one-band model for impurity states in n-type many-valley semiconductor has been extended by self-consistent many-body and unrestricted Hartree-Fock approaches. The formulations are presented in order to discuss the shallow donor states in semiconductors. The impurity band splits into two Hubbard bands, presenting different aspects of the impurity states when the many-valley effects of the host conduction band are considered. These effects turn out to be essential for a better interpretation of the theoretical and experimental results. The results agree with some theoretical calculations and experimental findings.

Zinc Oxide (ZnO) and Silicon Carbide (SiC) are prominent materials with large applicability such ... more Zinc Oxide (ZnO) and Silicon Carbide (SiC) are prominent materials with large applicability such as optoelectronic nanodevices and for instance ultraviolet detectors. There is lack of important information about optical transitions beyond the indirect band gap energy (BGE) of 4H-SiC and even more for ZnO direct BGE grown on the former material. Using vapor-liquid-solid and the aqueous chemical growth methods we have grown ZnO nanorods on different substrates, such as quartz, n-and ptype porous silicon, and n-type 4H-SiC. Scanning electron microscopy (SEM) was employed to compare sample morphologies. The absorption was calculated employing a projector augmented wave (PAW) method. The measured absorption of ZnO nanorods, on different substrates, is lower than that observed for ZnO films on quartz substrate, in the low energy spectral range. It is observed a strong effect of 4H-SiC substrates on ZnO nanorod properties. Experiment and theory show a good agreement when the shape of the optical absorption is considered for both materials.

Journal of Applied Physics, 1996

We investigate the electrical properties of Bi-doped Si samples, prepared by ion implantation, in... more We investigate the electrical properties of Bi-doped Si samples, prepared by ion implantation, in a range of concentrations around and above the metal–nonmetal transition. Comparison between experimental and theoretical values of the resistivity brought out that in these samples a similar behavior is observed as for other n-doped Si, thus confirming the results obtained in the same range of impurity concentration, i.e., ρ(Sb)≤ρ(P)≤ρ(As)≤ρ(Bi).

Physical Review B - Condensed Matter and Materials Physics, 2000

The band-gap shift of the heavily single and double-donor doped systems Si:Bi and Si:P,Bi, prepar... more The band-gap shift of the heavily single and double-donor doped systems Si:Bi and Si:P,Bi, prepared by ion implantation, was investigated theoretically and experimentally at room temperature. The calculations were carried out within a framework of the random-phase approximation and the temperature and different manybody effects were taken into account. The experimental data were obtained with photoconductivity measurements. Theoretical and experimental results fall closely together in a wide range of donor concentration.

The optical absorption and the dielectric functions of PbI2 and Sb x Bi 1-x I 3 have been investi... more The optical absorption and the dielectric functions of PbI2 and Sb x Bi 1-x I 3 have been investigated experimentally by means of absorption measurements and spectroscopic ellipsometry respectively, and theoretically by a full-potential linear muffin-tin-orbital method. These materials have been recognized as very promising detector materials with large technological applicabilities. The calculated band-gap energies, optical absorption and the dielectric functions were found to be in a very good agreement with the experimental results. The electron-energy-loss functions are also obtained for both experiment and theory for comparison. The band-gap energy as a function of temperature, for PbI 2 has also been measured by optical absorption. The temperature dependence has been fitted by a new relation, and a discussion of this fitting is given.

Journal of Crystal Growth, 2014

Biomater. Sci., 2014

This communication describes a general method for templating fungal filaments with gold nanoparti... more This communication describes a general method for templating fungal filaments with gold nanoparticles that results in a gold replica of filaments after calcination of the biological template.