A5083223172- Semiconductor Quantum Structures and Devices
- Advanced Semiconductor Detectors and Materials
- Nanowire Synthesis and Applications
- Quantum Dots Synthesis And Properties
- GaN-based semiconductor devices and materials
- Chalcogenide Semiconductor Thin Films
- ZnO doping and properties
- Ga2O3 and related materials
- Semiconductor materials and interfaces
- Semiconductor materials and devices
- solar cell performance optimization
- Electron and X-Ray Spectroscopy Techniques
- Gas Sensing Nanomaterials and Sensors
- Integrated Circuits and Semiconductor Failure Analysis
- Metal and Thin Film Mechanics
- Force Microscopy Techniques and Applications
- Advanced Electron Microscopy Techniques and Applications
- Semiconductor Lasers and Optical Devices
- Non-Destructive Testing Techniques
- Quantum and electron transport phenomena
- Advancements in Semiconductor Devices and Circuit Design
- Electronic and Structural Properties of Oxides
- Advanced Materials Characterization Techniques
- 2D Materials and Applications
- Perovskite Materials and Applications
Universidad de Cádiz
2015-2024
Bellingham Technical College
2015
Hospital Universitario Puerto Real
2010
Centro Nacional de Microelectrónica
2003
Intermediate band solar cells (IBSCs) fabricated to date from In(Ga)As/GaAs quantum dot arrays (QD-IBSC) exhibit a efficiency (QE) that extends below bandgap energies. However, the production of sub-bandgap photocurrent relies often on thermal and/or tunneling escape carriers QDs, which is incompatible with preservation output voltage. In this work, we test effectiveness introducing thick GaAs spacer in addition an InAlGaAs strain relief layer (SRL) over QDs reduce carrier escape. From...
PbS nanocrystals entrapped in the hollow core of apoferritin protein cages are synthesized aqueous solution by both reassembly and nanoreactor routes. In cases, limits size quantum dot it can encapsulate to 8 nm provides a route creation stable near-infrared fluorescent composite.
Stacked layers of self-assembled In(Ga)As quantum rings on GaAs grown by solid source molecular beam epitaxy are studied ex situ atomic force microscopy (AFM), low temperature photoluminescence (PL) and cross-sectional transmission electron (XTEM). The influence the strain field InAs segregation surface morphology, optical properties vertical ordering three ring is analyzed for spacers between from 1.5 to 14 nm. AFM PL results show that samples with >6nm have morphology similar single...
By using a marker technique based on nanowire (NW) heterostructure, we have identified the Ga-limited and N-limited GaN NW growth regimes, which are shifted in comparison to those two-dimensional layers. The results show that Ga atoms diffusing along sidewalls significant contribution vertical growth. reducing substrate temperature, Ga-rich conditions locally activate lateral In contrast atoms, of Al N adatom diffusion is negligible. Finally, control GaN/AlN heterostructures NWs demonstrated.
ZnO microrods were grown by laser assisted flow deposition technique in order to study their luminescence behaviour the near band edge spectral region. Transmission electron microscopy analysis put evidence high crystallinity degree and microrod's compositional homogeneity. Photoluminescence revealed a dominant 3.31 eV emission. The correlation between this emission presence of surface states was investigated performing plasma treatments with hydrogen nitrogen. significant modifications...
Abstract 2D semiconductors (2SEM) can transform many sectors, from information and communication technology to healthcare. To date, top‐down approaches their fabrication, such as exfoliation of bulk crystals by “scotch‐tape,” are widely used, but have limited prospects for precise engineering functionalities scalability. Here, a bottom‐up technique based on epitaxy is used demonstrate high‐quality, wafer‐scale 2SEM the wide band gap gallium selenide (GaSe) compound. GaSe layers well‐defined...
Type-II self-assembled GaSb/GaAs nanostructures have been grown by molecular-beam epitaxy and studied atomic-force microscopy, transmission electron power-dependent magnetophotoluminescence. Nanostructures on the sample surface are found to be entirely dotlike, while capped predominantly ringlike. Moreover, an in situ anneal process applied after thinly capping dots is shown enhance severity of rings relax strain matrix proximity GaSb, resulting a change spatial configuration exciton...
In the last decade several prototypes of intermediate band solar cells (IBSCs) have been manufactured. So far, most these based on InAs/GaAs quantum dots (QDs) in order to implement IB material. The key operation principles theory are two photon sub-bandgap (SBG) photocurrent, and output voltage preservation, both experimentally demonstrated at low temperature. At room temperature (RT), however, thermal escape/relaxation between conduction (CB) prevents preservation. To improve this...
Abstract The built-in piezoelectric fields in group III-nitrides can act as road blocks on the way to maximizing efficiency of opto-electronic devices. In order overcome this limitation, a proper characterization these is necessary. work nano-beam electron diffraction scanning transmission microscopy mode has been used simultaneously measure strain state and induced GaN/AlN multiple quantum well system.
This paper investigates the effect of GaAsBi strain reduction layers (SRLs) on InAs QDs with different Bi fluxes to achieve nanostructures improved temperature stability. The SRLs are grown at a lower (370 °C) than usual capping for (510 °C). study finds that GaAs low temperatures reduces QD decomposition and leads larger pyramidal dots but also increases threading dislocation (TD) density. When adding layer, significant in TD density is observed, unexpected structural changes occur....
The effect of the capping process on morphology InAs/GaAs quantum dots (QDs) by using different GaAs-based layers (CLs), ranging from strain reduction to compensating layers, has been studied transmission microscopic techniques. For this, we have measured simultaneously height and diameter in buried uncapped QDs covering populations hundreds that are statistically reliable. First, QD population evolves all cases a pyramidal shape into more homogenous distribution with spherical-dome shape,...
Multi-junction solar cells made by assembling semiconductor materials with different bandgap energies have hold the record conversion efficiencies for many years and are currently approaching 50%. Theoretical efficiency limits make use of optimum designs right lattice constant-bandgap energy combination, which requires a 1.0-1.15 eV material lattice-matched to GaAs/Ge. Nevertheless, lack suitable is hindering achievement predicted efficiencies, since only candidates were up now complex...
The effects of a high ion dose irradiation on ${\text{TiO}}_{2}$ thin films under different conditions temperature and nature are discussed. We have shown that anatase irradiated with ${\text{N}}^{+}$ ions at room develop typical microstructure mounds voids open to the surface whereas irradiations 700 K generate pattern well-ordered nanorods aligned beam. formation these patterns is caused by simultaneous effect near film favoring structural mobilization defective network material. To...
c-axis aligned ZnO nanorods were deposited by vapor phase transport on textured chemical bath buffer layers. In this work, we examine the role of layer and how it influences deposition process using both scanning transmission electron microscopes related techniques. Vapor layers is a complex growth with many simultaneously occurring effects including (i) substantial morphological transformation at high temperature, which base nanorods; (ii) formation mixed amorphous/crystalline ZnxSi1–xOy...
This paper reports the formation and characterization of spherical GaAs quantum dots obtained by nanosecond pulsed laser ablation in a liquid (ethanol or methanol). The produced bare nanoparticles demonstrate rather narrow size distribution which depends on applied power density (from 4.25 to 13.9 J/cm2 our experiments) is as low 2.5 nm for highest used. absolute value average diameter also decreases significantly, from 13.7 8.7 nm, increases this interval. Due nanoparticle dispersion...
A procedure to quantitatively analyse the relationship between wetting layer (WL) and quantum dots (QDs) as a whole in statistical way is proposed. As we will show manuscript, it allows determining, not only proportion of deposited InAs held WL, but also average In content inside QDs. First, amount measured for calibration three different WL structures without QDs by two methodologies: strain mappings high-resolution transmission electron microscopy images compositional with ChemiSTEM x-ray...
The size and emission wavelength of self-assembled InAs∕InP(001) quantum wires (QWrs) is affected by the P∕As exchange process. In this work, we demonstrate in situ stress measurements that at InAs∕InP interface depends on surface reconstruction InAs starting its immediate evolution when arsenic cell closed. Accordingly, amount InP grown increases with substrate temperature a steplike way. These results allow us to engineer QWr for 1.3 1.55μm room selecting range temperatures which cap layer grown.
The compositional distribution in a self-assembled InAs(P) quantum wire grown by molecular beam epitaxy on an InP(001) substrate has been determined electron energy loss spectrum imaging. We have the strain and stress fields generated around this capped with 5 nm InP layer finite element calculations using as input map experimentally obtained. Preferential sites for nucleation of wires surface capping are predicted, based chemical potential minimization, from surface. preferential agree...
The formation of a quaternary InGaAsSb alloy is shown to occur in the core epitaxial GaSb capped InAs∕GaAs quantum dots emitting at 1.3μm. existence four constituent elements demonstrated by using spatially resolved low-loss electron energy loss spectroscopy and aberration-corrected high angle annular dark field scanning transmission microscopy. intermixing process giving rise this takes place despite large miscibility gap between InAs binary compounds, probably driven strain dots.
Photoluminescence (PL) studies of GaN/AlxGa1−xN quantum dots (QDs) in nanowires demonstrate an efficient carrier confinement, resulting thermally stable decay times up to 300 K. The evolution the PL transition energy as a function both QD height and Al mole fraction barriers, well time height, point out that built-in electric field is significantly smaller than value expected from spontaneous polarization discontinuity. This explained by uniaxial compressive strain spontaneously formed...