Helder Vinicius Avanço Galeti - Academia.edu (original) (raw)

Papers by Helder Vinicius Avanço Galeti

Journal of Applied Physics

The effect of Furnace Annealing (FA) and Rapid Thermal annealing (RTA) on the structural and opti... more The effect of Furnace Annealing (FA) and Rapid Thermal annealing (RTA) on the structural and optical properties of GaAs1 − xBix/GaAs single quantum wells grown on (001) and (311)B substrates by molecular beam epitaxy was investigated. The structural properties were investigated by high-resolution x-ray diffraction (HR-XRD) and Transmission Electron Microscopy. The Bi concentration profiles were determined by simulating the HR-XRD 2θ−ω scans using dynamical scattering theory to estimate the Bi content, lattice coherence, and quality of the interfaces. The Bi composition was found to be similar for both samples grown on (001) and (311)B GaAs substrates. However, the simulations indicate that the Bi composition is not only limited in the GaAsBi quantum well (QW) layer but also extends out of the GaAsBi QW toward the GaAs barrier. Photoluminescence (PL) measurements were performed as a function of temperature and laser power for samples with a nominal Bi composition of 3%. PL spectra showed that (001) and (311)B samples have different peak energies at 1.23 eV and 1.26 eV, respectively, at 10 K. After RTA at 300 °C for 2 min, the PL intensity of (311)B and (001) samples was enhanced by factors of ∼2.5 and 1.75, respectively. However, for the (001) and (311)B FA samples, an enhancement of the PL intensity by a factor of only 1.5 times could be achieved. The enhancement of PL intensity in annealed samples was interpreted in terms of PL activation energies, with a reduction in the alloy disorder and an increase in the Bi cluster.

Nanotechnology

Effective and controllable doping is instrumental for enabling the use of III-V semiconductor nan... more Effective and controllable doping is instrumental for enabling the use of III-V semiconductor nanowires (NWs) in practical electronics and optoelectronics applications. To this end, dopants are incorporated during self-catalyzed growth via vapor-liquid-solid mechanism through the catalyst droplet or by vapor-solid mechanism of the sidewall growth. The interplay of these mechanisms together with the competition between axial elongation and radial growth of NWs can result in dopant concentration gradients along the NW axis. Here, we report an investigation of Be-doped p-type GaAs NWs grown by the self-catalyzed method on lithography-free Si/SiO x templates. The influence of dopant incorporation on the structural properties of the NWs is analyzed by scanning and transmission electron microscopy. By combining spatially resolved Raman spectroscopy and transport characterization, we are able to estimate the carrier concentration, mobility and resistivity on single-NW level. We show that Be dopants are incorporated predominantly by vapor-solid mechanism for low Be flux, while the relative contribution of vapor-liquid-solid incorporation is increased for higher Be flux, resulting in axial dopant gradients that depend on the nominal doping level.

Semiconductor Science and Technology

In this paper, we report on the structural and optical properties of n-type Si-doped and p-type B... more In this paper, we report on the structural and optical properties of n-type Si-doped and p-type Be-doped GaAs(1−x)Bi x thin films grown by molecular beam epitaxy on (311)B GaAs substrates with nominal Bi content x = 5.4%. Similar samples without Bi were also grown for comparison purposes (n-type GaAs and p-type GaAs). X-ray diffraction (XRD), micro-Raman at room temperature, and photoluminescence measurements as a function of temperature and laser excitation power (P EXC) were performed to investigate their structural and optical properties. XRD results revealed that the Bi incorporation in both n-type and p-type doped GaAsBi was similar, despite that the samples present remarkable differences in the number of Bi related defects, non-radiative centers and alloy disorder. Particularly, our results evidence that the Bi-related defects in n- and p-doped GaAsBi alloys have important impact on the differences of their optical properties.

Nanoscale Research Letters

The performance of Ohmic contacts applied to semiconductor nanowires (NWs) is an important aspect... more The performance of Ohmic contacts applied to semiconductor nanowires (NWs) is an important aspect for enabling their use in electronic or optoelectronic devices. Due to the small dimensions and specific surface orientation of NWs, the standard processing technology widely developed for planar heterostructures cannot be directly applied. Here, we report on the fabrication and optimization of Pt/Ti/Pt/Au Ohmic contacts for p-type GaAs nanowires grown by molecular beam epitaxy. The devices were characterized by current–voltage (IV) measurements. The linearity of the IV characteristics curves of individual nanowires was optimized by adjusting the layout of the contact metal layers, the surface treatment prior to metal evaporation, and post-processing thermal annealing. Our results reveal that the contact resistance is remarkably decreased when a Pt layer is deposited on the GaAs nanowire prior to the traditional Ti/Pt/Au multilayer layout used for p-type planar GaAs. These findings are ...

Physical Review Materials

Todos os direitos reservados. A reprodução não-autorizada desta publicação, no todo ou em parte, ... more Todos os direitos reservados. A reprodução não-autorizada desta publicação, no todo ou em parte, o constitui violação dos direitos autorais (Lei n 9.610). CIP-Brasil. Catalogação-na-publicação.

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.

Superlattices and Microstructures, 2014

ABSTRACT The effects of long time thermal annealing at 200 °C on the optical and structural prope... more ABSTRACT The effects of long time thermal annealing at 200 °C on the optical and structural properties of GaAs1−xBix alloys were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and photoluminescence (PL). FESEM images show that bismuth islands nucleate on the surface and their diameter increases after annealing. It was observed a PL intensity enhancement and a small blue shift in PL peak energy after thermal annealing at 200 °C for 3 h of GaAs1−xBix alloys which was associated to the reduction of the density of defects. However these defects are not completed removed by thermal annealing although an important PL intensity improvement is observed.

Soil Science Society of America Journal, 2006

Fluorescence spectroscopy relies on the fluorescence emitted by rigid conjugated systems and thus... more Fluorescence spectroscopy relies on the fluorescence emitted by rigid conjugated systems and thus can be used to assess the soil organic matter (SOM) humification. This technique is generally applied to solution samples of humic substances, and so far no information exists about its applicability to whole untreated soil samples. The laserinduced fluorescence (LIF) spectroscopy is proposed as a novel technique to assess the organic matter humification in whole soil samples. We sampled the 0-to 2.5-, 2.5-to 5-, 5-to 10-, 10-to 15-, and 15-to 20-cm layers of three Oxisols of long-term experiments located in two sites of the Brazilian Cerrado. The humification index based on LIF spectroscopy (H LIF) of whole soil samples showed a close correlation with the humification indexes A 4 /A 1 , I 465 /I 399 , and A 465 obtained after fluorescence spectroscopy analysis of the dissolved humic acids. The H LIF in soils under native cerrado or subjected to no-tillage increased from the top to the deepest layer, which is consistent with the deposition of labile organic matter from plant residues on the soil surface. The soils subjected to conventional tillage, however, showed relatively constant H LIF along the profile, possibly because homogenization imparted by disturbance of the arable layer. Accordingly, for the two top layers, the soils under no-tillage showed a lower H LIF than for conventionally tilled soils. Laser-induced fluorescence spectroscopy is a promising technique to assess humification in whole soil samples, particularly in Oxisols, which due to high concentration of Fe 31 are not feasible to electron spin resonance (ESR) and Carbon-13 nuclear magnetic resonance (13 C NMR) spectroscopy, unless previous treatment is employed.

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.

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.

Nanoscale Research Letters, 2012

We have studied the polarized resolved photoluminescence of n-type GaAs/AlAs/GaAlAs resonant tunn... more We have studied the polarized resolved photoluminescence of n-type GaAs/AlAs/GaAlAs resonant tunneling diodes under magnetic field parallel to the tunnel current. Under resonant tunneling conditions, we have observed two emission lines attributed to neutral (X) and negatively charged excitons (X −). We have observed a voltage-controlled circular polarization degree from the quantum well emission for both lines, with values up to −88% at 15 T at low voltages which are ascribed to an efficient spin injection from the 2D gases formed at the accumulation layers.

Journal of Physics D: Applied Physics, 2014

We investigate the electron spin dynamics in a p-type GaAs/AlAs resonant tunnelling device by mea... more We investigate the electron spin dynamics in a p-type GaAs/AlAs resonant tunnelling device by measuring the time-and polarized-resolved photoluminescence (PL) from the GaAs quantum well under a high magnetic field (15 T). The voltage dependence of the PL transients have revealed various tunnelling processes with different time constants that give rise to distinct spin-polarized carriers injected into the double-barrier structure.

Journal of Physics D: Applied Physics, 2014

ABSTRACT We have investigated the effect of long thermal annealing (3 h) at 200 °C on the physica... more ABSTRACT We have investigated the effect of long thermal annealing (3 h) at 200 °C on the physical properties of GaBiAs layers with a Bi concentration of 3% by using photoluminescence (PL) and polarized resolved PL under magnetic fields up to 14 T. The PL intensity and the diamagnetic shift of the annealed samples increased substantially. This indicates a reduction of carrier/exciton localization due to defects. In addition, it was found that the degree of the electron spin polarization increases up 41% at 14 T after thermal annealing due to the reduction of the density of defects.

Applied Physics Letters, 2011

We have investigated the polarized-resolved photoluminescence from the contact layers and the qua... more We have investigated the polarized-resolved photoluminescence from the contact layers and the quantum-well in an n-type GaAs/GaAlAs resonant tunneling diode for magnetic fields up to 19 T. The optical emission from the GaAs contact layers comprises the recombination from highly spinpolarized two-dimensional electron and hole gases with free tunneling carriers. Both the energy position and intensity of this indirect recombination are voltage-dependent and show remarkably abrupt variations near scattering-assisted tunneling resonances. Our results show that these two dimensional gases act as spin-polarized sources for carriers tunneling through the well in resonant tunneling diodes. V

Journal of Alloys and Compounds

Journal of Physics D: Applied Physics, 2013

In this work, we have investigated the spin polarization from two-dimensional hole gases (2DHG) f... more In this work, we have investigated the spin polarization from two-dimensional hole gases (2DHG) formed in p-i-p GaAs/AlAs resonant tunnelling diodes (RTDs) under magnetic field parallel to the tunnel current. We have observed that the polarization degree from the quantum well (QW) and the 2DHG formed at the accumulation layer is highly voltage and light sensitive and exhibits a clear sign inversion. Our results indicate that the voltage dependence of the QW polarization degree is mainly due to an efficient hole-resonant tunnelling process through spin states of the QW. On the other hand, the voltage dependence of the 2DHG polarization degree seems to be dependent on the hole density which is controlled by the applied voltage across the RTDs.

Applied Physics Letters, 2007

Journal of Applied Physics, 2014

ABSTRACT In this paper, we have investigated the effect of Be acceptors on the electroluminescenc... more ABSTRACT In this paper, we have investigated the effect of Be acceptors on the electroluminescence and the spin polarization in GaAs/AlAs p-i-n resonant tunneling diodes. The quantum well emission comprise two main lines separated by ∼20 meV attributed to excitonic and Be-related transitions, which intensities show remarkably abrupt variations at critical voltages, particularly at the electron resonant peak where it shows a high-frequency bistability. The circular-polarization degree of the quantum-well electroluminescence also shows strong and abrupt variations at the critical bias voltages and it attains relatively large values (of ∼−75% at 15 T). These effects may be explored to design novel devices for spintronic applications such as a high-frequency spin-oscillators.

Journal of Applied Physics

The effect of Furnace Annealing (FA) and Rapid Thermal annealing (RTA) on the structural and opti... more The effect of Furnace Annealing (FA) and Rapid Thermal annealing (RTA) on the structural and optical properties of GaAs1 − xBix/GaAs single quantum wells grown on (001) and (311)B substrates by molecular beam epitaxy was investigated. The structural properties were investigated by high-resolution x-ray diffraction (HR-XRD) and Transmission Electron Microscopy. The Bi concentration profiles were determined by simulating the HR-XRD 2θ−ω scans using dynamical scattering theory to estimate the Bi content, lattice coherence, and quality of the interfaces. The Bi composition was found to be similar for both samples grown on (001) and (311)B GaAs substrates. However, the simulations indicate that the Bi composition is not only limited in the GaAsBi quantum well (QW) layer but also extends out of the GaAsBi QW toward the GaAs barrier. Photoluminescence (PL) measurements were performed as a function of temperature and laser power for samples with a nominal Bi composition of 3%. PL spectra showed that (001) and (311)B samples have different peak energies at 1.23 eV and 1.26 eV, respectively, at 10 K. After RTA at 300 °C for 2 min, the PL intensity of (311)B and (001) samples was enhanced by factors of ∼2.5 and 1.75, respectively. However, for the (001) and (311)B FA samples, an enhancement of the PL intensity by a factor of only 1.5 times could be achieved. The enhancement of PL intensity in annealed samples was interpreted in terms of PL activation energies, with a reduction in the alloy disorder and an increase in the Bi cluster.

Nanotechnology

Effective and controllable doping is instrumental for enabling the use of III-V semiconductor nan... more Effective and controllable doping is instrumental for enabling the use of III-V semiconductor nanowires (NWs) in practical electronics and optoelectronics applications. To this end, dopants are incorporated during self-catalyzed growth via vapor-liquid-solid mechanism through the catalyst droplet or by vapor-solid mechanism of the sidewall growth. The interplay of these mechanisms together with the competition between axial elongation and radial growth of NWs can result in dopant concentration gradients along the NW axis. Here, we report an investigation of Be-doped p-type GaAs NWs grown by the self-catalyzed method on lithography-free Si/SiO x templates. The influence of dopant incorporation on the structural properties of the NWs is analyzed by scanning and transmission electron microscopy. By combining spatially resolved Raman spectroscopy and transport characterization, we are able to estimate the carrier concentration, mobility and resistivity on single-NW level. We show that Be dopants are incorporated predominantly by vapor-solid mechanism for low Be flux, while the relative contribution of vapor-liquid-solid incorporation is increased for higher Be flux, resulting in axial dopant gradients that depend on the nominal doping level.

Semiconductor Science and Technology

In this paper, we report on the structural and optical properties of n-type Si-doped and p-type B... more In this paper, we report on the structural and optical properties of n-type Si-doped and p-type Be-doped GaAs(1−x)Bi x thin films grown by molecular beam epitaxy on (311)B GaAs substrates with nominal Bi content x = 5.4%. Similar samples without Bi were also grown for comparison purposes (n-type GaAs and p-type GaAs). X-ray diffraction (XRD), micro-Raman at room temperature, and photoluminescence measurements as a function of temperature and laser excitation power (P EXC) were performed to investigate their structural and optical properties. XRD results revealed that the Bi incorporation in both n-type and p-type doped GaAsBi was similar, despite that the samples present remarkable differences in the number of Bi related defects, non-radiative centers and alloy disorder. Particularly, our results evidence that the Bi-related defects in n- and p-doped GaAsBi alloys have important impact on the differences of their optical properties.

Nanoscale Research Letters

The performance of Ohmic contacts applied to semiconductor nanowires (NWs) is an important aspect... more The performance of Ohmic contacts applied to semiconductor nanowires (NWs) is an important aspect for enabling their use in electronic or optoelectronic devices. Due to the small dimensions and specific surface orientation of NWs, the standard processing technology widely developed for planar heterostructures cannot be directly applied. Here, we report on the fabrication and optimization of Pt/Ti/Pt/Au Ohmic contacts for p-type GaAs nanowires grown by molecular beam epitaxy. The devices were characterized by current–voltage (IV) measurements. The linearity of the IV characteristics curves of individual nanowires was optimized by adjusting the layout of the contact metal layers, the surface treatment prior to metal evaporation, and post-processing thermal annealing. Our results reveal that the contact resistance is remarkably decreased when a Pt layer is deposited on the GaAs nanowire prior to the traditional Ti/Pt/Au multilayer layout used for p-type planar GaAs. These findings are ...

Physical Review Materials

Todos os direitos reservados. A reprodução não-autorizada desta publicação, no todo ou em parte, ... more Todos os direitos reservados. A reprodução não-autorizada desta publicação, no todo ou em parte, o constitui violação dos direitos autorais (Lei n 9.610). CIP-Brasil. Catalogação-na-publicação.

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.

Superlattices and Microstructures, 2014

ABSTRACT The effects of long time thermal annealing at 200 °C on the optical and structural prope... more ABSTRACT The effects of long time thermal annealing at 200 °C on the optical and structural properties of GaAs1−xBix alloys were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and photoluminescence (PL). FESEM images show that bismuth islands nucleate on the surface and their diameter increases after annealing. It was observed a PL intensity enhancement and a small blue shift in PL peak energy after thermal annealing at 200 °C for 3 h of GaAs1−xBix alloys which was associated to the reduction of the density of defects. However these defects are not completed removed by thermal annealing although an important PL intensity improvement is observed.

Soil Science Society of America Journal, 2006

Fluorescence spectroscopy relies on the fluorescence emitted by rigid conjugated systems and thus... more Fluorescence spectroscopy relies on the fluorescence emitted by rigid conjugated systems and thus can be used to assess the soil organic matter (SOM) humification. This technique is generally applied to solution samples of humic substances, and so far no information exists about its applicability to whole untreated soil samples. The laserinduced fluorescence (LIF) spectroscopy is proposed as a novel technique to assess the organic matter humification in whole soil samples. We sampled the 0-to 2.5-, 2.5-to 5-, 5-to 10-, 10-to 15-, and 15-to 20-cm layers of three Oxisols of long-term experiments located in two sites of the Brazilian Cerrado. The humification index based on LIF spectroscopy (H LIF) of whole soil samples showed a close correlation with the humification indexes A 4 /A 1 , I 465 /I 399 , and A 465 obtained after fluorescence spectroscopy analysis of the dissolved humic acids. The H LIF in soils under native cerrado or subjected to no-tillage increased from the top to the deepest layer, which is consistent with the deposition of labile organic matter from plant residues on the soil surface. The soils subjected to conventional tillage, however, showed relatively constant H LIF along the profile, possibly because homogenization imparted by disturbance of the arable layer. Accordingly, for the two top layers, the soils under no-tillage showed a lower H LIF than for conventionally tilled soils. Laser-induced fluorescence spectroscopy is a promising technique to assess humification in whole soil samples, particularly in Oxisols, which due to high concentration of Fe 31 are not feasible to electron spin resonance (ESR) and Carbon-13 nuclear magnetic resonance (13 C NMR) spectroscopy, unless previous treatment is employed.

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.

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.

Nanoscale Research Letters, 2012

We have studied the polarized resolved photoluminescence of n-type GaAs/AlAs/GaAlAs resonant tunn... more We have studied the polarized resolved photoluminescence of n-type GaAs/AlAs/GaAlAs resonant tunneling diodes under magnetic field parallel to the tunnel current. Under resonant tunneling conditions, we have observed two emission lines attributed to neutral (X) and negatively charged excitons (X −). We have observed a voltage-controlled circular polarization degree from the quantum well emission for both lines, with values up to −88% at 15 T at low voltages which are ascribed to an efficient spin injection from the 2D gases formed at the accumulation layers.

Journal of Physics D: Applied Physics, 2014

We investigate the electron spin dynamics in a p-type GaAs/AlAs resonant tunnelling device by mea... more We investigate the electron spin dynamics in a p-type GaAs/AlAs resonant tunnelling device by measuring the time-and polarized-resolved photoluminescence (PL) from the GaAs quantum well under a high magnetic field (15 T). The voltage dependence of the PL transients have revealed various tunnelling processes with different time constants that give rise to distinct spin-polarized carriers injected into the double-barrier structure.

Journal of Physics D: Applied Physics, 2014

ABSTRACT We have investigated the effect of long thermal annealing (3 h) at 200 °C on the physica... more ABSTRACT We have investigated the effect of long thermal annealing (3 h) at 200 °C on the physical properties of GaBiAs layers with a Bi concentration of 3% by using photoluminescence (PL) and polarized resolved PL under magnetic fields up to 14 T. The PL intensity and the diamagnetic shift of the annealed samples increased substantially. This indicates a reduction of carrier/exciton localization due to defects. In addition, it was found that the degree of the electron spin polarization increases up 41% at 14 T after thermal annealing due to the reduction of the density of defects.

Applied Physics Letters, 2011

We have investigated the polarized-resolved photoluminescence from the contact layers and the qua... more We have investigated the polarized-resolved photoluminescence from the contact layers and the quantum-well in an n-type GaAs/GaAlAs resonant tunneling diode for magnetic fields up to 19 T. The optical emission from the GaAs contact layers comprises the recombination from highly spinpolarized two-dimensional electron and hole gases with free tunneling carriers. Both the energy position and intensity of this indirect recombination are voltage-dependent and show remarkably abrupt variations near scattering-assisted tunneling resonances. Our results show that these two dimensional gases act as spin-polarized sources for carriers tunneling through the well in resonant tunneling diodes. V

Journal of Alloys and Compounds

Journal of Physics D: Applied Physics, 2013

In this work, we have investigated the spin polarization from two-dimensional hole gases (2DHG) f... more In this work, we have investigated the spin polarization from two-dimensional hole gases (2DHG) formed in p-i-p GaAs/AlAs resonant tunnelling diodes (RTDs) under magnetic field parallel to the tunnel current. We have observed that the polarization degree from the quantum well (QW) and the 2DHG formed at the accumulation layer is highly voltage and light sensitive and exhibits a clear sign inversion. Our results indicate that the voltage dependence of the QW polarization degree is mainly due to an efficient hole-resonant tunnelling process through spin states of the QW. On the other hand, the voltage dependence of the 2DHG polarization degree seems to be dependent on the hole density which is controlled by the applied voltage across the RTDs.

Applied Physics Letters, 2007

Journal of Applied Physics, 2014

ABSTRACT In this paper, we have investigated the effect of Be acceptors on the electroluminescenc... more ABSTRACT In this paper, we have investigated the effect of Be acceptors on the electroluminescence and the spin polarization in GaAs/AlAs p-i-n resonant tunneling diodes. The quantum well emission comprise two main lines separated by ∼20 meV attributed to excitonic and Be-related transitions, which intensities show remarkably abrupt variations at critical voltages, particularly at the electron resonant peak where it shows a high-frequency bistability. The circular-polarization degree of the quantum-well electroluminescence also shows strong and abrupt variations at the critical bias voltages and it attains relatively large values (of ∼−75% at 15 T). These effects may be explored to design novel devices for spintronic applications such as a high-frequency spin-oscillators.