Larbi Sfaxi - Academia.edu (original) (raw)

Papers by Larbi Sfaxi

Research paper thumbnail of Critical layer thickness enhancement of InAs overgrowth on porous GaAs

Journal of Crystal Growth, 2003

In the present work we have investigated the initial stage of InAs layer grown on porous GaAs (p-... more In the present work we have investigated the initial stage of InAs layer grown on porous GaAs (p-GaAs) substrate by using reflection high-energy electron diffraction (RHEED) and low temperature photoluminescence (PL). RHEED measurements show that the 2D-3D growth mode transition appears after a deposition of 4.2 atomic monolayer (ML) of InAs, which is higher than that deposited on nominal GaAs (1.7 ML). PL investigations show two luminescence bands at 1.24 and 1.38 eV. The 1.24 eV PL peak emission is associated to the radiative transitions in InAs quantum dots (QDs), whereas the 1.38 eV PL peak emission is attributed to the InAs wetting layer (WL). The results show that p-GaAs is a promising candidate to obtain a reduced QDs size distribution, and to grow pseudomorphic epitaxial layer on GaAs substrate with higher indium concentration.

Research paper thumbnail of Article Towards InAs/InGaAs/GaAs Quantum Dot Solar Cells Directly Grown on Si Substrate

This paper reports on an initial assessment of the direct growth of In(Ga)As/GaAs quantum dots (Q... more This paper reports on an initial assessment of the direct growth of In(Ga)As/GaAs quantum dots (QDs) solar cells on nanostructured surface Si substrate by molecular beam epitaxy (MBE). The effect of inserting 40 InAs/InGaAs/GaAs QDs layers in the intrinsic region of the heterojunction pin-GaAs/n +-Si was evaluated using photocurrent spectroscopy in comparison with pin-GaAs/n +-Si and pin-GaAs/GaAs without QDs. The results reveal the clear contribution of the QDs layers to the improvement of the spectral response up to 1200 nm. The novel structure has been studied by X ray diffraction (XRD), photoluminescence spectroscopy (PL) and transmission electron microscopy (TEM). These results provide considerable insights into low cost III-V material-based solar cells.

Research paper thumbnail of Efficiency improvement of single-junction InGaP solar cells fabricated by a novel micro-hole array surface texture process

Semiconductor Science and Technology, 2009

In this study, single-junction InGaP solar cells fabricated by a novel micro-hole array surface t... more In this study, single-junction InGaP solar cells fabricated by a novel micro-hole array surface texture process are presented. The characteristics of the single-junction InGaP solar cells with and without the micro-hole array surface texture are studied. An increase of 10.4% in short-circuit current is found when a single-junction InGaP solar cell is fabricated by the micro-hole array surface texture process. The conversion efficiency measured under one-sun air mass 1.5 global illumination at room temperature can also be improved from 13.8% to 15.9% when the size of the micro-holes is 5.3 μm and the period of micro-hole array is designed to 5 μm.

Research paper thumbnail of Optimisation of the physical properties of InAs/InGaAs/GaAs QDs heterostructures embedded p-i-n GaAs solar cell

International Journal of Nanotechnology, 2013

Research paper thumbnail of Long-wavelength emission from single InAs quantum dots layer grown on porous GaAs substrate

Microelectronics Journal, 2005

In this paper, we present the growth and photoluminescence (PL) results of InAs quantum dots (QDs... more In this paper, we present the growth and photoluminescence (PL) results of InAs quantum dots (QDs) on a p-type porous GaAs (001) substrate. It has been shown that critical layer thickness of InAs overgrowth on porous GaAs has been enhanced compared to that deposited on nominal GaAs. Using porous GaAs substrate, growth interruption and depositing 10 atomic monolayer (ML) In 0.4 Ga 0.6 As on InAs QDs, photoluminescence measured at 10 K exhibits an emission at 0.739 eV (w1.67 mm) with an ultranarrow full width at half maximum (FWHM) of 16 meV. This emission represents the longer wavelength obtained up to date to our knowledge and has been attributed to the radiative transition in the InAs QDs.

Research paper thumbnail of Strain Effects on Optical Properties of (In,Ga)As-Capped InAs Quantum Dots Grown by Molecular Beam Epitaxy on GaAs (113)A Substrate

International Journal of Spectroscopy, 2011

We have investigated the optical properties of InAs/GaAs (113)A quantum dots grown by molecular b... more We have investigated the optical properties of InAs/GaAs (113)A quantum dots grown by molecular beam epitaxy (MBE) capped by (In,Ga)As. Reflection high-energy electron diffraction (RHEED) is used to investigate the formation process of InAs quantum dots (QDs). A broadening of the PL emission due to size distribution of the dots, when InAs dots are capped by GaAs, was observed. A separation between large and small quantum dots, when they are encapsulated by InGaAs, was shown due to hydrostatic and biaxial strain action on large and small dots grown under specifically growth conditions. The PL polarization measurements have shown that the small dots require an elongated form, but the large dots present a quasi-isotropic behavior.

Research paper thumbnail of Etude de transport et de magnetotransport dans des gaz d'electrons modules lateralement a l'echelle nanometrique

L'objet de cette these est d'etudier theoriquement et experimentalement les proprietes de... more L'objet de cette these est d'etudier theoriquement et experimentalement les proprietes de transport et de magnetotransport de gaz electroniques bidimensionnels modules lateralement, obtenus en epitaxie par jets moleculaires sur des substrats de gaas vicinaux. Les effets observes sont les suivants: * anisotropie de resistivite et effet de masse negative (a champ magnetique nul). * magnetoresistance positive (a faible champ magnetique). * absence de clivage de spin pour un champ magnetique moyen

Research paper thumbnail of Theoretical Study of Excitonic Complexes in GaAs/AlGaAs Quantum Dots Grown by Filling of Nanoholes

In this work, a theoretical study of the electronic and the optical properties of a new family of... more In this work, a theoretical study of the electronic and the optical properties of a new family of strain-free GaAs/AlGaAs quantum dots (QDs) obtained by AlGaAs nanohole filling is presented. The considered model consists of solving the three-dimensional effective-mass Schrödinger equation, thus providing a complete description of the neutral and charged complex excitons’ fine structure. The QD size effect on carrier confinement energies, wave functions, and s-p splitting is studied. The direct Coulomb interaction impact on the calculated s and p states’ transition energies is investigated. The behaviour of the binding energy of neutral and charged excitons (X− and X+) and biexciton XX versus QD height is studied. The addition of the correlation effect allows to explain the nature of biexcitons often observed experimentally.

Research paper thumbnail of Experimental and theoretical study of thermally activated carrier transfer in InAs/GaAs multilayer quantum dots

In this paper, we have investigated the thermally activated carriers transfer mechanism in closel... more In this paper, we have investigated the thermally activated carriers transfer mechanism in closely stacked InAs/GaAs quantum dots (QDs) by means of steady-state photoluminescence (PL) and time-resolved photoluminescence measurements. The 10 K PL spectrum exhibits double-emission peaks where the excitation power dependence reveals that these emission peaks are attributed to large and small QD groups. With increasing the sample temperature, an abnormal line-width shrinkage of large QDs (LQDs) is observed. The increase in PL decay lifetime of LQDs versus temperature is nicely explained as the electron and hole wave function overlap between dot layers induced by vertical electronic coupling effect. Using a thermal escape model, the activation energies for PL thermal quenching at high temperatures (above 80K) were derived from fitting the temperature-dependent PL decay lifetime data of LQDs and SQDs. The determined activation energies show that the escape of electron-hole pairs from QDs ...

Research paper thumbnail of Piezoelectric field effects on sensitivity of Hall sensors based on AlGaAs/InGaAs/GaAs heterostructures

The sensitivity and performance of Hall sensors depends on the electron mobility of its substrate... more The sensitivity and performance of Hall sensors depends on the electron mobility of its substrate. With the aim to design a substrate capable of operating at high-absolute magnetic sensitivity and high current-related sensitivity we investigated the theoretical consequences of utilizing a high-index GaAs substrate in AlGaAs/InGaAs/GaAs heterostructures. The shape of the confining potential, the sub-band energies, the eigen envelope wave functions, and the Fermi energy in the InGaAs channel were calculated self-consistently at low temperature, taking into account exchange-correlation, strain, and piezoelectric effects. The piezoelectric field significantly increased the electron density (n s ) in the channel when the structure was grown on a GaAs (111)A substrate. This implies that one can have a wider spacer layer without altering n s , with the result of enhanced electron mobility. These data suggest that AlGaAs/InGaAs/GaAs heterostructures have high electron mobility and low sheet...

Research paper thumbnail of Spectroscopic ellipsometry study of barrier width effect in self-organized InGaAs/GaAs QDs laser diodes

Molecular beam epitaxy (MBE) is used to grow InGaAs/GaAs quantum dots (QDs) laser diodes (LDs) wi... more Molecular beam epitaxy (MBE) is used to grow InGaAs/GaAs quantum dots (QDs) laser diodes (LDs) with different barrier widths (5, 10 and 15 nm) at 580 oC on GaAs substrates. Optical properties of the InGaAs/GaAs QDs LDs have been investigated by using the spectroscopic ellipsometry (SE) technique. A general oscillator optical model has been utilized to fit the experimental data in order to obtain the LD layer thicknesses, refractive index and absorption coefficient. The dielectric function, the energy band gap and the surface and volume energy loss functions are computed in the energy range 1-6 eV. The optical properties of the deposited InGaAs/GaAs QDs LDs are found to be affected by the barrier width, which give more insight into carriers dynamics and optical parameters in these devices. The refractive indices, the extinction coefficients and the dielectric constants of the LDs with barrier widths 15 and 10 nm are relatively larger than those of the LD with barrier width 5 nm. Thes...

Research paper thumbnail of Ex-Situ Thermal Treatment Effects on the Temperature Dependent Carriers Dynamics in InAs/InGaAs/GaAs Quantum Dots

Crystals, Apr 28, 2018

The effects of post-growth thermal annealing of InAs QD with the high in-content strain reducing ... more The effects of post-growth thermal annealing of InAs QD with the high in-content strain reducing layer (SRL) on the temperature dependent PL properties have been investigated. The as-grown QD have shown an atypical behavior manifested by a sigmoidal emission energy and V-shaped linewidth evolution with temperature. These behaviors have been progressively glossed by subjecting the structure to post growth annealing at 650 • C and 750 • C for 50 s. The results are discussed in the frame of the localized states ensemble model, which reveals that carriers transfer take place by thermal activation to the continuum states of the strain-reducing layer and subsequent redistribution.

Research paper thumbnail of Thermal induced carrier’s transfer in bimodal size distribution InAs/GaAs quantum dots

Results in Physics

Abstract This work reports on the investigation of the thermal induced carriers’ transfer mechani... more Abstract This work reports on the investigation of the thermal induced carriers’ transfer mechanism in vertically stacked bimodal size distribution InAs/GaAs quantum dots (QD). A model treating the QD as a localized states ensemble (LSE) has been employed to fit the atypical temperature dependence of the photoluminescence (PL) emission energies and linewidth. The results suggest that thermally activated carriers transfer within the large size QD family occurs through the neighboring smaller size QD as an intermediate channel before direct carriers redistribution. The obtained activation energy suggests also the possible contribution of the wetting layer (WL) continuum states as a second mediator channel for carriers transfer.

Research paper thumbnail of Carrier dynamics of strain-engineered InAs quantum dots with (In)GaAs surrounding material

Research paper thumbnail of In/Ga intermixing effect on high-stacked InAs/In 0.11 Ga 0.89 As/GaAs self-assembled quantum-dots solar cells using photoluminescence spectroscopy and scanning near-field optical microscopy

Research paper thumbnail of Long wavelength vertically stacked InAs/GaAs(001) quantum dots with a bimodal size distribution: Optical properties and electronic coupling

Superlattices and Microstructures

A molecular beam epitaxy (MBE) grown vertically stacked InAs/GaAs(001) quantum dots (QDs) structu... more A molecular beam epitaxy (MBE) grown vertically stacked InAs/GaAs(001) quantum dots (QDs) structure emitting at 1.3 μm at room temperature has been investigated by photoluminescence (PL) experiment. The PL measurement has shown the coexistence of bimodal size distribution in the QD ensemble. Furthermore, the large size QDs are found to exhibit an interlayer vertical coupling in addition to a lateral coupling

Research paper thumbnail of Optical effects of Si-delta doping of GaAs spacer layer on the vertical coupled multi-stacked InAs/InGaAs/GaAs intermediate-band solar cells

International Journal of Nanotechnology, 2015

We report, in this work, the effects of Si-delta doped GaAs spacer layer on the optical propertie... more We report, in this work, the effects of Si-delta doped GaAs spacer layer on the optical properties of 20-stacked InAs/InGaAs/GaAs vertical coupled quantum dots heterostructures intermediate band solar cells (QD-IBSCs). The samples were grown by solid-source molecular beam epitaxy (SS-MBE) and investigated via photoluminescence (PL) and photocurrent (PC) spectroscopy. Two different families of quantum dots (QDs) were observed in the photoluminescence spectra and clearly identified in the atomic force microscopy image (AFM). With doping the GaAs spacer layer an opposite optical effect compared with previous works is investigated, the PL spectrum shows a dramatic decrease in PL intensity and a remarkable peak shift to higher energy. This is may be due to the incorporation of non-radiative impurities by doping. Moreover, it results in the more frequent filling by the additional electron of the sub-band level in the InAs QDs and promoted by the strain driven In/Ga intermixing between InAs/InGaAs QDs and GaAs spacer layer. The PC measurement exhibits a drop of the photocurrent accompanied by weak absorption in the extended range with doping, which is in good agreement with the (PL) results.

Research paper thumbnail of Characterisation of the GaAs-based intermediate band solar cell with multi-stacked InAs/InGaAs quantum dots

International Journal of Nanotechnology, 2015

We report on both the photovoltaic and the optical properties of GaAs p-i-n solar cell (SC) and G... more We report on both the photovoltaic and the optical properties of GaAs p-i-n solar cell (SC) and GaAs p-i-n SC with multiple InAs quantum dot (QD) layers in the i-region. Current-voltage and impedance spectroscopy measurements have been used to characterise the two SC devices. Refractive index, extinction and absorption coefficients were deduced from spectroscopic ellipsometry. I-V measurements in dark and illumination conditions have been carried out to investigate the photovoltaic effect in these devices. Our results suggested that the presence of trap states could cause the degraded photovoltaic performance of the QD SC device. The C-V characteristics of the QD SC device show forward bias region with negative values of capacitance, which is caused by the filling process of the dots near the junction. The equivalent circuit model consisting of two-series connected RC networks with a series resistance Rs was found to give a good fit to the experimental data.

Research paper thumbnail of Theoretical analyses of the elastic and electronic properties of InAs QDs and QD-in-WELL structures grown on GaAs high index substrates

Journal of Alloys and Compounds, 2015

ABSTRACT We report a theoretical study of the wetting layer thickness, InxGa(1−x)As quantum-well ... more ABSTRACT We report a theoretical study of the wetting layer thickness, InxGa(1−x)As quantum-well thickness and Indium composition effects on the physical properties of InAs quantum dots (QDs) and quantum dots-in-well (QD-in-WELL) grown on GaAs high index substrates. Finite element method is used to calculate the strain, piezoelectric field distributions and the electronic structure. Coulomb interaction has been taken as a perturbation in the interband transition energy. The ground–state transition energy is influenced by the wetting layer thickness (WL) and the substrate orientation; however, it is not affected by the InGaAs quantum-well thickness. We have found that the tensile strain at the interface is the main factor responsible for the difficulty of self-assembled InAs QDs formation on GaAs(111) substrate. On the other hand, the stability of the relaxed strain into QD–IN–WELL depended on the Indium composition and the quantum-well thickness as well as the orientation substrate. The appropriate Indium composition in the InGaAs quantum-well is found to be 0.3 for the QD–IN–WELL grown on GaAs(111) and 0.2 for the QD–IN–WELL grown on GaAs(119). This work can be helpful to controlling the wavelength of QD–IN–WELL grown on high index substrates by changing the In composition or the quantum well-thickness.

Research paper thumbnail of Enhancement of the 2DEG density in AlGaAs/InGaAs/GaAs P-HEMTs structures grown by MBE on (311)A and (111)A GaAs substrates

Materials Science and Engineering: C, 2008

The pseudomorphic high electron mobility transistor (P-HEMT) structure materials Al0.33Ga0.7As/In... more The pseudomorphic high electron mobility transistor (P-HEMT) structure materials Al0.33Ga0.7As/In0.1Ga0.9As/GaAs have been grown by molecular beam epitaxy (MBE) on (311)A and (111)A GaAs substrates. The epitaxy of strain heterostructure on high index GaAs substrate has led to new growth phenomena, material properties and device applications. The photoluminescence (PL) spectra of the structures have been measured at low temperature. The dominant emission in the PL spectra is due to the recombination from the first electron (e1) subband to the first heavy-hole (hh1) subband (E11: e1–hh1). This feature (E11) is a relatively broad peak and has a typical asymmetric line shape. The transformation of the PL spectra in the close vicinity of the Fermi edge (EF) under different excitation densities gives strong evidence for the Fermi Edge Singularity (FES) existence. The density of the quasi-two-dimensional electron gas (2DEG) determined by PL study (nsPL), is in sufficient agreement with the values found from Hall measurements nsHall at 77 K. The results prove an increase of the electron density in sample grown on GaAs (111)A and (311)A rather than in equivalent sample grown on (001) GaAs substrate. This effect is in good agreement with our theoretical prediction, which is based on a self-consistent solution of the coupled Schrödinger and Poisson equations.

Research paper thumbnail of Critical layer thickness enhancement of InAs overgrowth on porous GaAs

Journal of Crystal Growth, 2003

In the present work we have investigated the initial stage of InAs layer grown on porous GaAs (p-... more In the present work we have investigated the initial stage of InAs layer grown on porous GaAs (p-GaAs) substrate by using reflection high-energy electron diffraction (RHEED) and low temperature photoluminescence (PL). RHEED measurements show that the 2D-3D growth mode transition appears after a deposition of 4.2 atomic monolayer (ML) of InAs, which is higher than that deposited on nominal GaAs (1.7 ML). PL investigations show two luminescence bands at 1.24 and 1.38 eV. The 1.24 eV PL peak emission is associated to the radiative transitions in InAs quantum dots (QDs), whereas the 1.38 eV PL peak emission is attributed to the InAs wetting layer (WL). The results show that p-GaAs is a promising candidate to obtain a reduced QDs size distribution, and to grow pseudomorphic epitaxial layer on GaAs substrate with higher indium concentration.

Research paper thumbnail of Article Towards InAs/InGaAs/GaAs Quantum Dot Solar Cells Directly Grown on Si Substrate

This paper reports on an initial assessment of the direct growth of In(Ga)As/GaAs quantum dots (Q... more This paper reports on an initial assessment of the direct growth of In(Ga)As/GaAs quantum dots (QDs) solar cells on nanostructured surface Si substrate by molecular beam epitaxy (MBE). The effect of inserting 40 InAs/InGaAs/GaAs QDs layers in the intrinsic region of the heterojunction pin-GaAs/n +-Si was evaluated using photocurrent spectroscopy in comparison with pin-GaAs/n +-Si and pin-GaAs/GaAs without QDs. The results reveal the clear contribution of the QDs layers to the improvement of the spectral response up to 1200 nm. The novel structure has been studied by X ray diffraction (XRD), photoluminescence spectroscopy (PL) and transmission electron microscopy (TEM). These results provide considerable insights into low cost III-V material-based solar cells.

Research paper thumbnail of Efficiency improvement of single-junction InGaP solar cells fabricated by a novel micro-hole array surface texture process

Semiconductor Science and Technology, 2009

In this study, single-junction InGaP solar cells fabricated by a novel micro-hole array surface t... more In this study, single-junction InGaP solar cells fabricated by a novel micro-hole array surface texture process are presented. The characteristics of the single-junction InGaP solar cells with and without the micro-hole array surface texture are studied. An increase of 10.4% in short-circuit current is found when a single-junction InGaP solar cell is fabricated by the micro-hole array surface texture process. The conversion efficiency measured under one-sun air mass 1.5 global illumination at room temperature can also be improved from 13.8% to 15.9% when the size of the micro-holes is 5.3 μm and the period of micro-hole array is designed to 5 μm.

Research paper thumbnail of Optimisation of the physical properties of InAs/InGaAs/GaAs QDs heterostructures embedded p-i-n GaAs solar cell

International Journal of Nanotechnology, 2013

Research paper thumbnail of Long-wavelength emission from single InAs quantum dots layer grown on porous GaAs substrate

Microelectronics Journal, 2005

In this paper, we present the growth and photoluminescence (PL) results of InAs quantum dots (QDs... more In this paper, we present the growth and photoluminescence (PL) results of InAs quantum dots (QDs) on a p-type porous GaAs (001) substrate. It has been shown that critical layer thickness of InAs overgrowth on porous GaAs has been enhanced compared to that deposited on nominal GaAs. Using porous GaAs substrate, growth interruption and depositing 10 atomic monolayer (ML) In 0.4 Ga 0.6 As on InAs QDs, photoluminescence measured at 10 K exhibits an emission at 0.739 eV (w1.67 mm) with an ultranarrow full width at half maximum (FWHM) of 16 meV. This emission represents the longer wavelength obtained up to date to our knowledge and has been attributed to the radiative transition in the InAs QDs.

Research paper thumbnail of Strain Effects on Optical Properties of (In,Ga)As-Capped InAs Quantum Dots Grown by Molecular Beam Epitaxy on GaAs (113)A Substrate

International Journal of Spectroscopy, 2011

We have investigated the optical properties of InAs/GaAs (113)A quantum dots grown by molecular b... more We have investigated the optical properties of InAs/GaAs (113)A quantum dots grown by molecular beam epitaxy (MBE) capped by (In,Ga)As. Reflection high-energy electron diffraction (RHEED) is used to investigate the formation process of InAs quantum dots (QDs). A broadening of the PL emission due to size distribution of the dots, when InAs dots are capped by GaAs, was observed. A separation between large and small quantum dots, when they are encapsulated by InGaAs, was shown due to hydrostatic and biaxial strain action on large and small dots grown under specifically growth conditions. The PL polarization measurements have shown that the small dots require an elongated form, but the large dots present a quasi-isotropic behavior.

Research paper thumbnail of Etude de transport et de magnetotransport dans des gaz d'electrons modules lateralement a l'echelle nanometrique

L'objet de cette these est d'etudier theoriquement et experimentalement les proprietes de... more L'objet de cette these est d'etudier theoriquement et experimentalement les proprietes de transport et de magnetotransport de gaz electroniques bidimensionnels modules lateralement, obtenus en epitaxie par jets moleculaires sur des substrats de gaas vicinaux. Les effets observes sont les suivants: * anisotropie de resistivite et effet de masse negative (a champ magnetique nul). * magnetoresistance positive (a faible champ magnetique). * absence de clivage de spin pour un champ magnetique moyen

Research paper thumbnail of Theoretical Study of Excitonic Complexes in GaAs/AlGaAs Quantum Dots Grown by Filling of Nanoholes

In this work, a theoretical study of the electronic and the optical properties of a new family of... more In this work, a theoretical study of the electronic and the optical properties of a new family of strain-free GaAs/AlGaAs quantum dots (QDs) obtained by AlGaAs nanohole filling is presented. The considered model consists of solving the three-dimensional effective-mass Schrödinger equation, thus providing a complete description of the neutral and charged complex excitons’ fine structure. The QD size effect on carrier confinement energies, wave functions, and s-p splitting is studied. The direct Coulomb interaction impact on the calculated s and p states’ transition energies is investigated. The behaviour of the binding energy of neutral and charged excitons (X− and X+) and biexciton XX versus QD height is studied. The addition of the correlation effect allows to explain the nature of biexcitons often observed experimentally.

Research paper thumbnail of Experimental and theoretical study of thermally activated carrier transfer in InAs/GaAs multilayer quantum dots

In this paper, we have investigated the thermally activated carriers transfer mechanism in closel... more In this paper, we have investigated the thermally activated carriers transfer mechanism in closely stacked InAs/GaAs quantum dots (QDs) by means of steady-state photoluminescence (PL) and time-resolved photoluminescence measurements. The 10 K PL spectrum exhibits double-emission peaks where the excitation power dependence reveals that these emission peaks are attributed to large and small QD groups. With increasing the sample temperature, an abnormal line-width shrinkage of large QDs (LQDs) is observed. The increase in PL decay lifetime of LQDs versus temperature is nicely explained as the electron and hole wave function overlap between dot layers induced by vertical electronic coupling effect. Using a thermal escape model, the activation energies for PL thermal quenching at high temperatures (above 80K) were derived from fitting the temperature-dependent PL decay lifetime data of LQDs and SQDs. The determined activation energies show that the escape of electron-hole pairs from QDs ...

Research paper thumbnail of Piezoelectric field effects on sensitivity of Hall sensors based on AlGaAs/InGaAs/GaAs heterostructures

The sensitivity and performance of Hall sensors depends on the electron mobility of its substrate... more The sensitivity and performance of Hall sensors depends on the electron mobility of its substrate. With the aim to design a substrate capable of operating at high-absolute magnetic sensitivity and high current-related sensitivity we investigated the theoretical consequences of utilizing a high-index GaAs substrate in AlGaAs/InGaAs/GaAs heterostructures. The shape of the confining potential, the sub-band energies, the eigen envelope wave functions, and the Fermi energy in the InGaAs channel were calculated self-consistently at low temperature, taking into account exchange-correlation, strain, and piezoelectric effects. The piezoelectric field significantly increased the electron density (n s ) in the channel when the structure was grown on a GaAs (111)A substrate. This implies that one can have a wider spacer layer without altering n s , with the result of enhanced electron mobility. These data suggest that AlGaAs/InGaAs/GaAs heterostructures have high electron mobility and low sheet...

Research paper thumbnail of Spectroscopic ellipsometry study of barrier width effect in self-organized InGaAs/GaAs QDs laser diodes

Molecular beam epitaxy (MBE) is used to grow InGaAs/GaAs quantum dots (QDs) laser diodes (LDs) wi... more Molecular beam epitaxy (MBE) is used to grow InGaAs/GaAs quantum dots (QDs) laser diodes (LDs) with different barrier widths (5, 10 and 15 nm) at 580 oC on GaAs substrates. Optical properties of the InGaAs/GaAs QDs LDs have been investigated by using the spectroscopic ellipsometry (SE) technique. A general oscillator optical model has been utilized to fit the experimental data in order to obtain the LD layer thicknesses, refractive index and absorption coefficient. The dielectric function, the energy band gap and the surface and volume energy loss functions are computed in the energy range 1-6 eV. The optical properties of the deposited InGaAs/GaAs QDs LDs are found to be affected by the barrier width, which give more insight into carriers dynamics and optical parameters in these devices. The refractive indices, the extinction coefficients and the dielectric constants of the LDs with barrier widths 15 and 10 nm are relatively larger than those of the LD with barrier width 5 nm. Thes...

Research paper thumbnail of Ex-Situ Thermal Treatment Effects on the Temperature Dependent Carriers Dynamics in InAs/InGaAs/GaAs Quantum Dots

Crystals, Apr 28, 2018

The effects of post-growth thermal annealing of InAs QD with the high in-content strain reducing ... more The effects of post-growth thermal annealing of InAs QD with the high in-content strain reducing layer (SRL) on the temperature dependent PL properties have been investigated. The as-grown QD have shown an atypical behavior manifested by a sigmoidal emission energy and V-shaped linewidth evolution with temperature. These behaviors have been progressively glossed by subjecting the structure to post growth annealing at 650 • C and 750 • C for 50 s. The results are discussed in the frame of the localized states ensemble model, which reveals that carriers transfer take place by thermal activation to the continuum states of the strain-reducing layer and subsequent redistribution.

Research paper thumbnail of Thermal induced carrier’s transfer in bimodal size distribution InAs/GaAs quantum dots

Results in Physics

Abstract This work reports on the investigation of the thermal induced carriers’ transfer mechani... more Abstract This work reports on the investigation of the thermal induced carriers’ transfer mechanism in vertically stacked bimodal size distribution InAs/GaAs quantum dots (QD). A model treating the QD as a localized states ensemble (LSE) has been employed to fit the atypical temperature dependence of the photoluminescence (PL) emission energies and linewidth. The results suggest that thermally activated carriers transfer within the large size QD family occurs through the neighboring smaller size QD as an intermediate channel before direct carriers redistribution. The obtained activation energy suggests also the possible contribution of the wetting layer (WL) continuum states as a second mediator channel for carriers transfer.

Research paper thumbnail of Carrier dynamics of strain-engineered InAs quantum dots with (In)GaAs surrounding material

Research paper thumbnail of In/Ga intermixing effect on high-stacked InAs/In 0.11 Ga 0.89 As/GaAs self-assembled quantum-dots solar cells using photoluminescence spectroscopy and scanning near-field optical microscopy

Research paper thumbnail of Long wavelength vertically stacked InAs/GaAs(001) quantum dots with a bimodal size distribution: Optical properties and electronic coupling

Superlattices and Microstructures

A molecular beam epitaxy (MBE) grown vertically stacked InAs/GaAs(001) quantum dots (QDs) structu... more A molecular beam epitaxy (MBE) grown vertically stacked InAs/GaAs(001) quantum dots (QDs) structure emitting at 1.3 μm at room temperature has been investigated by photoluminescence (PL) experiment. The PL measurement has shown the coexistence of bimodal size distribution in the QD ensemble. Furthermore, the large size QDs are found to exhibit an interlayer vertical coupling in addition to a lateral coupling

Research paper thumbnail of Optical effects of Si-delta doping of GaAs spacer layer on the vertical coupled multi-stacked InAs/InGaAs/GaAs intermediate-band solar cells

International Journal of Nanotechnology, 2015

We report, in this work, the effects of Si-delta doped GaAs spacer layer on the optical propertie... more We report, in this work, the effects of Si-delta doped GaAs spacer layer on the optical properties of 20-stacked InAs/InGaAs/GaAs vertical coupled quantum dots heterostructures intermediate band solar cells (QD-IBSCs). The samples were grown by solid-source molecular beam epitaxy (SS-MBE) and investigated via photoluminescence (PL) and photocurrent (PC) spectroscopy. Two different families of quantum dots (QDs) were observed in the photoluminescence spectra and clearly identified in the atomic force microscopy image (AFM). With doping the GaAs spacer layer an opposite optical effect compared with previous works is investigated, the PL spectrum shows a dramatic decrease in PL intensity and a remarkable peak shift to higher energy. This is may be due to the incorporation of non-radiative impurities by doping. Moreover, it results in the more frequent filling by the additional electron of the sub-band level in the InAs QDs and promoted by the strain driven In/Ga intermixing between InAs/InGaAs QDs and GaAs spacer layer. The PC measurement exhibits a drop of the photocurrent accompanied by weak absorption in the extended range with doping, which is in good agreement with the (PL) results.

Research paper thumbnail of Characterisation of the GaAs-based intermediate band solar cell with multi-stacked InAs/InGaAs quantum dots

International Journal of Nanotechnology, 2015

We report on both the photovoltaic and the optical properties of GaAs p-i-n solar cell (SC) and G... more We report on both the photovoltaic and the optical properties of GaAs p-i-n solar cell (SC) and GaAs p-i-n SC with multiple InAs quantum dot (QD) layers in the i-region. Current-voltage and impedance spectroscopy measurements have been used to characterise the two SC devices. Refractive index, extinction and absorption coefficients were deduced from spectroscopic ellipsometry. I-V measurements in dark and illumination conditions have been carried out to investigate the photovoltaic effect in these devices. Our results suggested that the presence of trap states could cause the degraded photovoltaic performance of the QD SC device. The C-V characteristics of the QD SC device show forward bias region with negative values of capacitance, which is caused by the filling process of the dots near the junction. The equivalent circuit model consisting of two-series connected RC networks with a series resistance Rs was found to give a good fit to the experimental data.

Research paper thumbnail of Theoretical analyses of the elastic and electronic properties of InAs QDs and QD-in-WELL structures grown on GaAs high index substrates

Journal of Alloys and Compounds, 2015

ABSTRACT We report a theoretical study of the wetting layer thickness, InxGa(1−x)As quantum-well ... more ABSTRACT We report a theoretical study of the wetting layer thickness, InxGa(1−x)As quantum-well thickness and Indium composition effects on the physical properties of InAs quantum dots (QDs) and quantum dots-in-well (QD-in-WELL) grown on GaAs high index substrates. Finite element method is used to calculate the strain, piezoelectric field distributions and the electronic structure. Coulomb interaction has been taken as a perturbation in the interband transition energy. The ground–state transition energy is influenced by the wetting layer thickness (WL) and the substrate orientation; however, it is not affected by the InGaAs quantum-well thickness. We have found that the tensile strain at the interface is the main factor responsible for the difficulty of self-assembled InAs QDs formation on GaAs(111) substrate. On the other hand, the stability of the relaxed strain into QD–IN–WELL depended on the Indium composition and the quantum-well thickness as well as the orientation substrate. The appropriate Indium composition in the InGaAs quantum-well is found to be 0.3 for the QD–IN–WELL grown on GaAs(111) and 0.2 for the QD–IN–WELL grown on GaAs(119). This work can be helpful to controlling the wavelength of QD–IN–WELL grown on high index substrates by changing the In composition or the quantum well-thickness.

Research paper thumbnail of Enhancement of the 2DEG density in AlGaAs/InGaAs/GaAs P-HEMTs structures grown by MBE on (311)A and (111)A GaAs substrates

Materials Science and Engineering: C, 2008

The pseudomorphic high electron mobility transistor (P-HEMT) structure materials Al0.33Ga0.7As/In... more The pseudomorphic high electron mobility transistor (P-HEMT) structure materials Al0.33Ga0.7As/In0.1Ga0.9As/GaAs have been grown by molecular beam epitaxy (MBE) on (311)A and (111)A GaAs substrates. The epitaxy of strain heterostructure on high index GaAs substrate has led to new growth phenomena, material properties and device applications. The photoluminescence (PL) spectra of the structures have been measured at low temperature. The dominant emission in the PL spectra is due to the recombination from the first electron (e1) subband to the first heavy-hole (hh1) subband (E11: e1–hh1). This feature (E11) is a relatively broad peak and has a typical asymmetric line shape. The transformation of the PL spectra in the close vicinity of the Fermi edge (EF) under different excitation densities gives strong evidence for the Fermi Edge Singularity (FES) existence. The density of the quasi-two-dimensional electron gas (2DEG) determined by PL study (nsPL), is in sufficient agreement with the values found from Hall measurements nsHall at 77 K. The results prove an increase of the electron density in sample grown on GaAs (111)A and (311)A rather than in equivalent sample grown on (001) GaAs substrate. This effect is in good agreement with our theoretical prediction, which is based on a self-consistent solution of the coupled Schrödinger and Poisson equations.