Y. Gobato - Academia.edu (original) (raw)

Papers by Y. Gobato

Research paper thumbnail of Kinetics of excitonic complexes on tunneling devices

Physical Review B, 2005

In this work we have investigated the effects of trion formation on the tunneling current from bo... more In this work we have investigated the effects of trion formation on the tunneling current from both experimental and theoretical viewpoints. We have measured the current-voltage characteristics and the quantum-well photoluminescence emission of GaAs-Ga 1−x Al x As n-i-n double barrier diodes. We have observed a preresonance shoulder in the current-voltage curve under high laser intensities associated with the formation of trions in the quantum well, which increase the number of free states in the resonant and excitonic levels, thus enhancing the tunneling mechanism. These excitonic complexes were detected through the photoluminescence spectra under bias. We have observed that the preresonance shoulder occurs under the same conditions for which a trion peak in the luminescence spectrum is present. This trion-assisted mechanism is terminated when neutral and charged excitons are dissociated either by thermal excitation or by scattering with free carriers in the quantum well. A phenomenological rate equation model has allowed us to confirm our assumptions on the effect of trion formation on the charge transport.

Research paper thumbnail of Optical and Structural Properties of Emerging Dilute III-V Bismides

Research paper thumbnail of A comparative photoluminescence study on Mn-Free GaAs/AlAs and Mn-containing Ga 1-x Mn x As/AlAs quantum wells (QWs) grown on various orientations by MBE

Philosophical Magazine, 2015

Research paper thumbnail of Antiferromagnetism induced by oxygen vacancies in V 2 O 5 polycrystals synthesized by the Pechini method

Journal of Physics D: Applied Physics, 2015

Research paper thumbnail of Spin polarization of carriers in resonant tunneling devices containing InAs self-assembled quantum dots

Superlattices and Microstructures, 2015

Research paper thumbnail of Resonant Tunneling in a Tilted Magnetic Field

Research paper thumbnail of Visible to infrared low temperature luminescence of Er(3+), Nd(3+) and Sm(3+) in CaSnO3 phosphors

Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine, 2015

Novel stannate phosphor, orthorhombic CaSnO3 phosphors doped with Er(3+), Nd(3+) and Sm(3+) have ... more Novel stannate phosphor, orthorhombic CaSnO3 phosphors doped with Er(3+), Nd(3+) and Sm(3+) have been synthesized by a conventional solid-state method under N2+H2 gas flow. Visible and near-infrared photoluminescence (PL) properties were investigated as function of laser power and temperature. It was observed that all dopant ions are well incorporated in CaSnO3 and are responsible for the optical emission in the temperature range of 10-300K. PL peaks at 490, 546, 656, 696, 894, 1065, and 1344nm were observed for the CaSnO3:Nd(3+) phosphor and associated to f-f transition of Nd(3+) ion. Emissions at 564, 600-607, 646-656 and 714nm were detected for the CaSnO3:Sm(3+). The strongest one, observed at 600nm, was associated to (4)G5/2→(6)H7/2 of Sm(3). Emission lines at 528, 548, 662 at 852nm were also seen for CaSnO3:Er(3+) and correspond to Er(3+) intra-4f(n) shell transitions. In addition, at low temperatures, a stark splitting of the 4f electron energy levels of the Er(3+) ions were o...

Research paper thumbnail of <title>Tunnelling of photogenerated holes through landau levels in GaAs/AlGaAs double barrier diodes</title>

Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Research paper thumbnail of Magnetotunneling analysis of the scattering processes in a double-barrier structure with a two-dimensional emitter

Physical review. B, Condensed matter, Jan 15, 1991

Research paper thumbnail of Selection-rule breakdown in coherent resonant tunneling in a tilted magnetic field

Research paper thumbnail of Strain and localization effects in InGaAs(N) quantum wells: Tuning the magnetic response

Journal of Applied Physics, 2014

ABSTRACT We investigated effects of localization and strain on the optical and magneto-optical pr... more ABSTRACT We investigated effects of localization and strain on the optical and magneto-optical properties of diluted nitrogen III–V quantum wells theoretically and experimentally. High-resolution x-ray diffraction, photoluminescence (PL), and magneto-PL measurements under high magnetic fields up to 15 T were performed at low temperatures. Bir-Pikus Hamiltonian formalism was used to study the influence of strain, confinement, and localization effects. The circularly polarized magneto-PL was interpreted considering localization aspects in the valence band ground state. An anomalous behavior of the electron-hole pair magnetic shift was observed at low magnetic fields, ascribed to the increase in the exciton reduced mass due to the negative effective mass of the valence band ground state.

Research paper thumbnail of The search for superconductivity in the system Y 1-x Pr x Sr y Ba 2-y Cu 3 O 7-d

Research paper thumbnail of Circular polarization in n-type resonant tunneling diodes with Si delta-doping in the quantum well

2014 29th Symposium on Microelectronics Technology and Devices (SBMicro), 2014

In this work, we have investigated magneto-transport and polarization resolved photoluminescence ... more In this work, we have investigated magneto-transport and polarization resolved photoluminescence of a GaAs IAIGaAs resonant tunneling diode with Si delta-doping at the center of the quantum well under a magnetic field parallel to the tunnel current. Three resonant peaks were observed in the current-voltage characteristics curve (J(V)) which were associated to donor-assisted resonant tunneling, electron resonant tunneling and to phonon assisted resonant tunneling. The optical emission from GaAs contact layers shows evidence of highly spin-polarized two-dimensional electron and hole gases which affect the spin-polarization of carriers in the well. The quantum well photoluminescence shows strong circular polarization degrees with values up to 85% under J 5T at the donor assisted resonant tunneling peak voltage. Our results can be exploited for fitture development of voltage-controlled spintronics devices.

Research paper thumbnail of Quantum box resonant tunneling spectroscopy: Experiments and modelisation

Superlattices and Microstructures, 1992

ABSTRACT We have calculated the potential profile and the electronic levels in resonant tunneling... more ABSTRACT We have calculated the potential profile and the electronic levels in resonant tunneling double barrier structures with nanometric lateral dimensions (≤ 500 nm) for various contact doping. At biases for which the box states (laterally confined quantum well) are resonant with the emitter Fermi level, fine structures are expected in the resonant tunneling current. Comparison with I(V) characteristics measured on nanometric GaAs/GaAlAs and GaAs/GaAlAs/InGaAs resonant tunneling diodes shows that our model accounts for the resonance bias voltage and explains the shape of the current peak. The fine structure observed in the current peak provides a spectroscopy of the confined states in the quantum box.

Research paper thumbnail of Resonant tunneling in laterally confined double barrier structures

Solid State Communications, 1993

ABSTRACT We have calculated the potential profile, the electronic levels, the transmission and th... more ABSTRACT We have calculated the potential profile, the electronic levels, the transmission and the coherent current in resonant tunneling double barrier structures with nanometric lateral dimensions. The results of these 1D-0D tunneling calculations are discussed in terms of spectroscopy of the 0D states and compared to experimental data previously reported.

Research paper thumbnail of The temperature dependence of electrical and optical properties in InAs/GaAs and GaAs/InAs/AlAs self-assembled quantum dots

Semiconductor Science and Technology, 2006

In this paper, we report on the effects of the environment on the properties of an ensemble of In... more In this paper, we report on the effects of the environment on the properties of an ensemble of InAs self-assembled quantum dots. The properties presented by the electrons confined at the dots can be tuned by adjusting some parameters of the environment. Using capacitance-voltage and photoluminescence measurements, we observed an increase in the thermal stability of zero-dimensional electron gas when the dots were grown in a period of a GaAs/AlAs superlattice. We believe that the parameter responsible for the thermal stability observed here was the increase of the electrical impedance of the device. In addition, electrical and optical measurements enabled us to study the thermal stability of electrons located at the dots grown in the GaAs bulk and in the aforementioned superlattice.

Research paper thumbnail of Magneto-optical investigation of two-dimensional gases in n-type resonant tunneling diodes

Semiconductor Science and Technology, 2012

We have studied the polarized emission from the contact layers and the quantum well of asymmetric... more We have studied the polarized emission from the contact layers and the quantum well of asymmetric n-type GaAs/GaAlAs resonant tunneling diodes under high magnetic fields (up to 19 T) parallel to the tunnel current. The photoluminescence from the GaAs contact layers shows evidence of the recombination from a two-dimensional hole gas accumulated next to the GaAlAs barrier and free carriers. Both the energy position and the intensity of this emission are voltage dependent. In addition, the photoluminescence from the two-dimensional hole gas and quantum well is strongly spin-polarized under the applied voltage and high magnetic fields. Pronounced oscillatory features are observed in the magnetic field dependence of the polarization degree from the quantum well and the two-dimensional hole emissions at integer filling factors. The obtained data show that resonant tunneling diodes are interesting systems to study the physical properties of voltage-controlled two-dimensional gases in the accumulation layers and quantum well.

Research paper thumbnail of Aharonov-Bohm Interference in Neutral Excitons: Effects of Built-In Electric Fields

Physical Review Letters, 2010

We report a comprehensive discussion of quantum interference effects due to the finite structure ... more We report a comprehensive discussion of quantum interference effects due to the finite structure of neutral excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. The signatures of built-in electric fields and temperature on quantum interference are demonstrated by theoretical models that describe the modulation of the interference pattern and confirmed by complementary experimental procedures.

Research paper thumbnail of Role of X valley on the dynamics of electron transport through a GaAs/AlAs double-barrier structure

Physical Review B, 2008

The transport of electrons through a GaAs/AlAs double-barrier structure with p-type doped contact... more The transport of electrons through a GaAs/AlAs double-barrier structure with p-type doped contacts was investigated using time-resolved photoluminescence spectroscopy. Under illumination, the current-voltage characteristics of the device present two additional features attributed, respectively, to resonant ⌫-⌫ and ⌫-X electron tunneling. Optical measurements for biases where these two alternative transport mechanisms have competitive probabilities revealed an unusual carrier dynamics. The quantum well emission is strongly delayed and we observe a remarkable nonlinear effect where the emission intensity decreases at the arrival of a laser pulse. We propose a simple model that adequately describes our results where we assume that the indirecttransition rate depends on the density of electrons accumulated along the structure.

Research paper thumbnail of Kinetics of excitonic complexes on tunneling devices

Physical Review B, 2005

In this work we have investigated the effects of trion formation on the tunneling current from bo... more In this work we have investigated the effects of trion formation on the tunneling current from both experimental and theoretical viewpoints. We have measured the current-voltage characteristics and the quantum-well photoluminescence emission of GaAs-Ga 1−x Al x As n-i-n double barrier diodes. We have observed a preresonance shoulder in the current-voltage curve under high laser intensities associated with the formation of trions in the quantum well, which increase the number of free states in the resonant and excitonic levels, thus enhancing the tunneling mechanism. These excitonic complexes were detected through the photoluminescence spectra under bias. We have observed that the preresonance shoulder occurs under the same conditions for which a trion peak in the luminescence spectrum is present. This trion-assisted mechanism is terminated when neutral and charged excitons are dissociated either by thermal excitation or by scattering with free carriers in the quantum well. A phenomenological rate equation model has allowed us to confirm our assumptions on the effect of trion formation on the charge transport.

Research paper thumbnail of Kinetics of excitonic complexes on tunneling devices

Physical Review B, 2005

In this work we have investigated the effects of trion formation on the tunneling current from bo... more In this work we have investigated the effects of trion formation on the tunneling current from both experimental and theoretical viewpoints. We have measured the current-voltage characteristics and the quantum-well photoluminescence emission of GaAs-Ga 1−x Al x As n-i-n double barrier diodes. We have observed a preresonance shoulder in the current-voltage curve under high laser intensities associated with the formation of trions in the quantum well, which increase the number of free states in the resonant and excitonic levels, thus enhancing the tunneling mechanism. These excitonic complexes were detected through the photoluminescence spectra under bias. We have observed that the preresonance shoulder occurs under the same conditions for which a trion peak in the luminescence spectrum is present. This trion-assisted mechanism is terminated when neutral and charged excitons are dissociated either by thermal excitation or by scattering with free carriers in the quantum well. A phenomenological rate equation model has allowed us to confirm our assumptions on the effect of trion formation on the charge transport.

Research paper thumbnail of Optical and Structural Properties of Emerging Dilute III-V Bismides

Research paper thumbnail of A comparative photoluminescence study on Mn-Free GaAs/AlAs and Mn-containing Ga 1-x Mn x As/AlAs quantum wells (QWs) grown on various orientations by MBE

Philosophical Magazine, 2015

Research paper thumbnail of Antiferromagnetism induced by oxygen vacancies in V 2 O 5 polycrystals synthesized by the Pechini method

Journal of Physics D: Applied Physics, 2015

Research paper thumbnail of Spin polarization of carriers in resonant tunneling devices containing InAs self-assembled quantum dots

Superlattices and Microstructures, 2015

Research paper thumbnail of Resonant Tunneling in a Tilted Magnetic Field

Research paper thumbnail of Visible to infrared low temperature luminescence of Er(3+), Nd(3+) and Sm(3+) in CaSnO3 phosphors

Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine, 2015

Novel stannate phosphor, orthorhombic CaSnO3 phosphors doped with Er(3+), Nd(3+) and Sm(3+) have ... more Novel stannate phosphor, orthorhombic CaSnO3 phosphors doped with Er(3+), Nd(3+) and Sm(3+) have been synthesized by a conventional solid-state method under N2+H2 gas flow. Visible and near-infrared photoluminescence (PL) properties were investigated as function of laser power and temperature. It was observed that all dopant ions are well incorporated in CaSnO3 and are responsible for the optical emission in the temperature range of 10-300K. PL peaks at 490, 546, 656, 696, 894, 1065, and 1344nm were observed for the CaSnO3:Nd(3+) phosphor and associated to f-f transition of Nd(3+) ion. Emissions at 564, 600-607, 646-656 and 714nm were detected for the CaSnO3:Sm(3+). The strongest one, observed at 600nm, was associated to (4)G5/2→(6)H7/2 of Sm(3). Emission lines at 528, 548, 662 at 852nm were also seen for CaSnO3:Er(3+) and correspond to Er(3+) intra-4f(n) shell transitions. In addition, at low temperatures, a stark splitting of the 4f electron energy levels of the Er(3+) ions were o...

Research paper thumbnail of <title>Tunnelling of photogenerated holes through landau levels in GaAs/AlGaAs double barrier diodes</title>

Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Research paper thumbnail of Magnetotunneling analysis of the scattering processes in a double-barrier structure with a two-dimensional emitter

Physical review. B, Condensed matter, Jan 15, 1991

Research paper thumbnail of Selection-rule breakdown in coherent resonant tunneling in a tilted magnetic field

Research paper thumbnail of Strain and localization effects in InGaAs(N) quantum wells: Tuning the magnetic response

Journal of Applied Physics, 2014

ABSTRACT We investigated effects of localization and strain on the optical and magneto-optical pr... more ABSTRACT We investigated effects of localization and strain on the optical and magneto-optical properties of diluted nitrogen III–V quantum wells theoretically and experimentally. High-resolution x-ray diffraction, photoluminescence (PL), and magneto-PL measurements under high magnetic fields up to 15 T were performed at low temperatures. Bir-Pikus Hamiltonian formalism was used to study the influence of strain, confinement, and localization effects. The circularly polarized magneto-PL was interpreted considering localization aspects in the valence band ground state. An anomalous behavior of the electron-hole pair magnetic shift was observed at low magnetic fields, ascribed to the increase in the exciton reduced mass due to the negative effective mass of the valence band ground state.

Research paper thumbnail of The search for superconductivity in the system Y 1-x Pr x Sr y Ba 2-y Cu 3 O 7-d

Research paper thumbnail of Circular polarization in n-type resonant tunneling diodes with Si delta-doping in the quantum well

2014 29th Symposium on Microelectronics Technology and Devices (SBMicro), 2014

In this work, we have investigated magneto-transport and polarization resolved photoluminescence ... more In this work, we have investigated magneto-transport and polarization resolved photoluminescence of a GaAs IAIGaAs resonant tunneling diode with Si delta-doping at the center of the quantum well under a magnetic field parallel to the tunnel current. Three resonant peaks were observed in the current-voltage characteristics curve (J(V)) which were associated to donor-assisted resonant tunneling, electron resonant tunneling and to phonon assisted resonant tunneling. The optical emission from GaAs contact layers shows evidence of highly spin-polarized two-dimensional electron and hole gases which affect the spin-polarization of carriers in the well. The quantum well photoluminescence shows strong circular polarization degrees with values up to 85% under J 5T at the donor assisted resonant tunneling peak voltage. Our results can be exploited for fitture development of voltage-controlled spintronics devices.

Research paper thumbnail of Quantum box resonant tunneling spectroscopy: Experiments and modelisation

Superlattices and Microstructures, 1992

ABSTRACT We have calculated the potential profile and the electronic levels in resonant tunneling... more ABSTRACT We have calculated the potential profile and the electronic levels in resonant tunneling double barrier structures with nanometric lateral dimensions (≤ 500 nm) for various contact doping. At biases for which the box states (laterally confined quantum well) are resonant with the emitter Fermi level, fine structures are expected in the resonant tunneling current. Comparison with I(V) characteristics measured on nanometric GaAs/GaAlAs and GaAs/GaAlAs/InGaAs resonant tunneling diodes shows that our model accounts for the resonance bias voltage and explains the shape of the current peak. The fine structure observed in the current peak provides a spectroscopy of the confined states in the quantum box.

Research paper thumbnail of Resonant tunneling in laterally confined double barrier structures

Solid State Communications, 1993

ABSTRACT We have calculated the potential profile, the electronic levels, the transmission and th... more ABSTRACT We have calculated the potential profile, the electronic levels, the transmission and the coherent current in resonant tunneling double barrier structures with nanometric lateral dimensions. The results of these 1D-0D tunneling calculations are discussed in terms of spectroscopy of the 0D states and compared to experimental data previously reported.

Research paper thumbnail of The temperature dependence of electrical and optical properties in InAs/GaAs and GaAs/InAs/AlAs self-assembled quantum dots

Semiconductor Science and Technology, 2006

In this paper, we report on the effects of the environment on the properties of an ensemble of In... more In this paper, we report on the effects of the environment on the properties of an ensemble of InAs self-assembled quantum dots. The properties presented by the electrons confined at the dots can be tuned by adjusting some parameters of the environment. Using capacitance-voltage and photoluminescence measurements, we observed an increase in the thermal stability of zero-dimensional electron gas when the dots were grown in a period of a GaAs/AlAs superlattice. We believe that the parameter responsible for the thermal stability observed here was the increase of the electrical impedance of the device. In addition, electrical and optical measurements enabled us to study the thermal stability of electrons located at the dots grown in the GaAs bulk and in the aforementioned superlattice.

Research paper thumbnail of Magneto-optical investigation of two-dimensional gases in n-type resonant tunneling diodes

Semiconductor Science and Technology, 2012

We have studied the polarized emission from the contact layers and the quantum well of asymmetric... more We have studied the polarized emission from the contact layers and the quantum well of asymmetric n-type GaAs/GaAlAs resonant tunneling diodes under high magnetic fields (up to 19 T) parallel to the tunnel current. The photoluminescence from the GaAs contact layers shows evidence of the recombination from a two-dimensional hole gas accumulated next to the GaAlAs barrier and free carriers. Both the energy position and the intensity of this emission are voltage dependent. In addition, the photoluminescence from the two-dimensional hole gas and quantum well is strongly spin-polarized under the applied voltage and high magnetic fields. Pronounced oscillatory features are observed in the magnetic field dependence of the polarization degree from the quantum well and the two-dimensional hole emissions at integer filling factors. The obtained data show that resonant tunneling diodes are interesting systems to study the physical properties of voltage-controlled two-dimensional gases in the accumulation layers and quantum well.

Research paper thumbnail of Aharonov-Bohm Interference in Neutral Excitons: Effects of Built-In Electric Fields

Physical Review Letters, 2010

We report a comprehensive discussion of quantum interference effects due to the finite structure ... more We report a comprehensive discussion of quantum interference effects due to the finite structure of neutral excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. The signatures of built-in electric fields and temperature on quantum interference are demonstrated by theoretical models that describe the modulation of the interference pattern and confirmed by complementary experimental procedures.

Research paper thumbnail of Role of X valley on the dynamics of electron transport through a GaAs/AlAs double-barrier structure

Physical Review B, 2008

The transport of electrons through a GaAs/AlAs double-barrier structure with p-type doped contact... more The transport of electrons through a GaAs/AlAs double-barrier structure with p-type doped contacts was investigated using time-resolved photoluminescence spectroscopy. Under illumination, the current-voltage characteristics of the device present two additional features attributed, respectively, to resonant ⌫-⌫ and ⌫-X electron tunneling. Optical measurements for biases where these two alternative transport mechanisms have competitive probabilities revealed an unusual carrier dynamics. The quantum well emission is strongly delayed and we observe a remarkable nonlinear effect where the emission intensity decreases at the arrival of a laser pulse. We propose a simple model that adequately describes our results where we assume that the indirecttransition rate depends on the density of electrons accumulated along the structure.

Research paper thumbnail of Kinetics of excitonic complexes on tunneling devices

Physical Review B, 2005

In this work we have investigated the effects of trion formation on the tunneling current from bo... more In this work we have investigated the effects of trion formation on the tunneling current from both experimental and theoretical viewpoints. We have measured the current-voltage characteristics and the quantum-well photoluminescence emission of GaAs-Ga 1−x Al x As n-i-n double barrier diodes. We have observed a preresonance shoulder in the current-voltage curve under high laser intensities associated with the formation of trions in the quantum well, which increase the number of free states in the resonant and excitonic levels, thus enhancing the tunneling mechanism. These excitonic complexes were detected through the photoluminescence spectra under bias. We have observed that the preresonance shoulder occurs under the same conditions for which a trion peak in the luminescence spectrum is present. This trion-assisted mechanism is terminated when neutral and charged excitons are dissociated either by thermal excitation or by scattering with free carriers in the quantum well. A phenomenological rate equation model has allowed us to confirm our assumptions on the effect of trion formation on the charge transport.