A5035487979- Semiconductor Quantum Structures and Devices
- GaN-based semiconductor devices and materials
- Semiconductor materials and devices
- Advanced Semiconductor Detectors and Materials
- Ga2O3 and related materials
- Semiconductor materials and interfaces
- Advancements in Semiconductor Devices and Circuit Design
- Metal and Thin Film Mechanics
- Semiconductor Lasers and Optical Devices
- ZnO doping and properties
- Nanowire Synthesis and Applications
- Silicon and Solar Cell Technologies
- Quantum and electron transport phenomena
- Photocathodes and Microchannel Plates
- Electron and X-Ray Spectroscopy Techniques
- Acoustic Wave Resonator Technologies
- Molecular Junctions and Nanostructures
- Spectroscopy and Laser Applications
- Electronic and Structural Properties of Oxides
- Diamond and Carbon-based Materials Research
- Gas Sensing Nanomaterials and Sensors
- Atomic and Subatomic Physics Research
- Solid-state spectroscopy and crystallography
- Silicon Nanostructures and Photoluminescence
- Integrated Circuits and Semiconductor Failure Analysis
Oberlin College
2023
Universidad Politécnica de Madrid
2002-2012
University of Padua
2010
Qinetiq (United Kingdom)
2010
Shizuoka University
2008
Institute of Microelectronics
2008
Universidad Complutense de Madrid
2005
Keystone College
1999
Instituto Politécnico Nacional
1998
Centro Nacional de Microelectrónica
1986
III nitrides have become the most exciting challenge in optoelectronic materials last decade. Their intrinsic properties and an intense technological effort made possible fabrication of reliable versatile detectors for short wavelengths.
A model to explain the behaviour of GaN photoconductive detectors is proposed, and it based on idea a volume modulation rather than carrier density modulation. Space charge regions inside semiconductor produce variation conductive when carriers are photogenerated. The strong non-exponential photocurrent decays result from capture processes over barriers associated with space regions. By means computer simulation, this explains quite well current photoconductor devices predicts their time...
We report on the fabrication and characterization of AlGaN metal–semiconductor–metal photodiodes with sharp cutoff wavelengths from 365 to 310 nm. The detectors are visible blind, an ultraviolet/visible contrast about 4 orders magnitude. photocurrent scales linearly optical power for photon energies both over below band gap, supporting absence photoconductive gain related space-charge regions. No persistent photoconductivity effects have been detected. Time response is limited by RC product...
Short-time heat treatments in a H2 flow, and under an As vapor, have been performed on n-type p-type GaAs crystals. Acceptors are created at the surface proceed to interior. The changes carrier concentration as function of vapor pressure showed acceptors be associated with vacancies.
Schottky barrier photovoltaic detectors have been fabricated on n-AlxGa1−xN(0⩽x⩽0.35) and p-GaN epitaxial layers grown sapphire. Their characteristics analyzed modeled, in order to determine the physical mechanisms that limit their performance. The influence of material properties device parameters is discussed. Our analysis considers front back illumination distinguishes between devices ideal high-quality state-of-the-art heteroepitaxial AlxGa1−xN. In former case, low doping levels are...
Si-doped GaAs and dilute AlxGa1−xAs alloys under hydrostatic pressure have been studied using deep level transient spectroscopy (DLTS). In the DLTS spectrum of DX center is a single peak. AlGaAs however, multiple peaks, resulting from different thermal emission rates donors having numbers Al atoms as near neighbors, are observed. The dependence electron occupation individual levels shows that larger number Si donor, lower energy position level.
Gold and nickel Schottky barrier photovoltaic detectors have been fabricated on Si-doped AlxGa1−xN layers (0⩽x⩽0.22) grown sapphire by metalorganic vapor phase epitaxy. Responsivity is independent of the metal or diode size, also incident power in range measured (10 mW/m2–2 kW/m2). A higher visible rejection has observed spectral response Au photodiodes (>103). Time resistance-capacitance limited, with time constants as short 14 ns Al0.22Ga0.78N diodes. Low frequency noise studies are...
Hydrostatic pressure techniques together with deep level transient spectroscopy (DLTS) measurements have shown that the Si-DX center in GaAlAs is linked to L-conduction-band minimum. When hydrostatic applied a 74% Al content sample, an exponential reduction of DLTS signal observed. This dependence arises from DX filling factor (electron occupancy) due increasing X-L energy difference pressure. Our results, previous data, also show capture barrier height originating lattice relaxation...
This paper reports on the search for ultralight dark matter in form of axions and photons using an innovative experimental design which earth serves as a transducer converting into characteristic magnetic field signal. The magnetometers used to detect expected patterns are placed areas noise sources, such anthropogenic ones, minimal. Although no conclusive detection is reported, limits set models various parameter ranges prospects refining methodology presented.
Hardness and Young’s modulus were measured in AlGaN thin films with different Al content, using a nanoindentation technique. slightly decreases increasing ranging from 20.2 to 19.5 GPa for content 0.09 0.27, respectively. No significant variations of observed. The resulting value is 375 GPa. Discontinuities load–displacement curves found, which are associated dislocation nucleation. threshold load this discontinuity depends on the conditions test. Below load, sample surface flexes...
Al x Ga 1−x N/GaN heterostructure field-effect transistors with different concentrations (0.15<x<0.25) and barrier widths (150 Å<WB<350 Å) have been fabricated characterized. Experimental results were analyzed by using a self-consistent solution of the Schrödinger Poisson equations proper boundary conditions. The total (piezoelectric spontaneous) polarization has included as fitting parameter in calculations. From analysis transistor charge-control experimental...
The “kink” effect in AlGaN/GaN high electron mobility transistor current-voltage characteristics is shown to be associated with the epitaxial growth and unaffected by fabrication process or substrate device wafers from two epitaxy sources three foundries. We demonstrate that there a direct correlation between presence of broad yellow cathodoluminescence band. On basis generally accepted models for luminescence, we propose kink due deep levels GaN buffer layer which decrease drain current...
The diagonal and nondiagonal components of the transverse magnetoresistance have been measured, over a wide magnetic field range, in modulated doped Al0.25Ga0.75N/GaN heterostructures. component shows electron–electron interaction whole Shubnikov–de Hass (SdH) oscillations superimposed at high field, weak localization very low field. SdH are evidence existence two-dimensional electron gas (2DEG) heterostructure. Only one kind carriers is present with an density 1.01×1017 m−2, effective mass...
Deep-center characterization by deep-level transient spectroscopy (DLTS) allows a direct determination of the trap thermal emission activation energy. However, capture barrier energy measurements, based on partial filling pulses increasing width, require quite different experimental processing and pose some hardware difficulties. In this letter we present new method to determine energy, one that requires constant-width obtains information from standard DLTS data. This technique has been...
Deep level transient spectroscopy in Si- and Sn-doped GaAlAs reveals a fine structure of the DX center thermal emission spectra under adequate filling pulse sampling window times. This is reproducible samples with Al mode fractions near 30% but it not detectable 85% content. All resolved peaks this have same energy quite different capture cross section (σ∞n). fact indicates that origin nonexponential behavior processes discrete broadening σ∞n due to alloy effect.
The band bending and carrier concentration profiles as a function of depth below the surface for oxidized InxGa1−xN alloys with composition range 0.39≤x≤1.00 are investigated using x-ray photoelectron, infrared reflection, optical absorption spectroscopies, solutions Poisson’s equation within modified Thomas–Fermi approximation. All these InGaN samples exhibit downward ranging from 0.19 to 0.66 eV high sheet charge density 5.0×1012 1.5×1013 cm−2. is more pronounced in most In-rich samples,...
We report the detection of phase separation an Al 1− x In N/GaN heterojunction grown close to lattice-matched conditions ( ∼ 0.18) by means Rutherford backscattering spectrometry in channelling geometry and high-resolution x-ray diffraction. An initial pseudomorphic growth film was found, with good single crystalline quality, nominal composition very low strain state. After ∼50 nm, a critical thickness is reached at which InN molar fraction films drops ∼15% same time quality degrade...
Be-doped GaN layers have been grown on Si(111) by molecular beam epitaxy. The relative Be concentration was measured secondary ion mass spectroscopy analysis. Photoluminescence spectra taken under continuous wave and time-resolved conditions. A new emission at 3.384 eV, which is probably related to substitutional Be, reported, together with its first second order phonon replica. Clear blue-shifts are observed when increasing temperature excitation power, suggesting that this associated a...
Transient capacitance and photocapacitance techniques have been used to study the characteristics of two electron traps related Te in GaAs1−xPx: Te. Levels En1 En2 thermal activation energies 0.17 0.27 eV, respectively, their emission capture rates deviate markedly from Schockley–Read–Hall theory for near band gap crossover compositions. Such centers are found 0.3<x≤1, linked X conduction minima, photoionization thresholds 0.5 1 respectively. Trap concentrations studied as a function...
This work reports on the growth by molecular beam epitaxy and characterization of InN/InGaN multiple quantum wells (MQWs) emitting at 1.5 μm. X-ray diffraction (XRD) spectra show satellite peaks up to second order. Estimated values well (3 nm) barrier (9 thicknesses were derived from transmission electron microscopy fit between experimental data simulated XRD spectra. Transmission simulations also confirmed that InGaN barriers are relaxed with respect GaN template, while InN MQWs grew under...
The effects of power and time conditions in situ <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{N}_{2}$</tex></formula> plasma treatment, prior to silicon nitride (SiN) passivation, were investigated on an AlGaN/GaN high-electron mobility transistor (HEMT). These studies reveal that is a critical parameter control the SiN/AlGaN interface quality, which directly affects 2-D electron gas...
The use of room- and low-temperature photoluminescence (PL) spectroscopy for the assessment n-type pseudomorphic AlGaAs/InGaAs/GaAs high-electron-mobility transistor structures is reported. We describe a method to determine InAs mole fraction x, channel layer thickness L, confined two-dimensional electron gas density (ns), based on comparison between PL transitions recombination energies derived from self-consistent calculations subband structure. A detailed analysis optical their dependence...