arXiv subjects

R. Jaramillo

Publications and source records attributed to R. Jaramillo.

At least 19 recordsLinked to original sources

arXiv2025

Effects of Neutron Irradiation on LGADs with Broad Multiplication Layer and varied Carbon-Enriched Doses: A Study on Timing Performance and Gain Deterioration

In this radiation tolerance study, Low Gain Avalanche Detectors (LGADs) with a carbon-enriched broad and shallow multiplication layer were examined in comparison to identical non-carbonated LGADs. Manufactured at IMB-CNM, the sensors underwent neutron irradiation at the TRIGRA reactor in Ljubljana, reaching a fluence of $2.5 \times 10^{15}n_{eq}cm^{-2}$. The results revealed a smaller deactivation of Boron and improved resistance to radiation in carbonated LGADs. The study demonstrated the potential benefits of carbon enrichment in mitigating radiation damage effects, particularly the acceptor removal mechanism, reducing the acceptor removal constant by more than a factor of two. Additionally, time resolution and collected charge degradation due to irradiation were observed, with carbonated samples exhibiting better radiation tolerance. A noise analysis focused on baseline noise and thermally generated pulses showed the presence of spurious thermal-generated pulses attributed to a excessive small distance between the gain layer end and the p-stop implant at the periphery of the pad for the characterized LGAD design; however, the operation performance of the devices was unaffected.

physics.ins-det↗

arXiv2025

The ILD Detector: A Versatile Detector for an Electron-Positron Collider at Energies up to 1 TeV

The International Large Detector, ILD, is a detector concept for an experiment at a future high energy lepton collider. The detector has been optimised for precision physics in a range of energies from 90~GeV to about 1~TeV. ILD features a high precision, large volume combined silicon and gaseous tracking system, together with a high granularity calorimeter, all inside a central solenoidal magnetic field. The paradigm of particle flow has been the guiding principle of the design of ILD. ILD is based mostly on technologies which have been demonstrated by extensive research and test programs. The ILD concept is proposed both for linear and circular lepton collider, be it at CERN or elsewhere. The concept has been developed by a group of nearly 60 institutes from around the world, and offers a well developed and powerful environment for science and technology studies at lepton colliders. In this document, the required performance of the detector, the proposed implementation and the readiness of the different technologies needed for the implementation are discussed.

hep-ex↗

arXiv2025

Epitaxial formation of ultrathin HfO2 on graphene by sequential oxidation

We demonstrate the formation of epitaxial, ultrathin hafnia (HfO2) on graphene. Monoclinic hafnia (m-HfO2) forms as the end of a series of sequential oxidation reactions. Starting from Hf metal grown epitaxially on graphene, oxidation leads first to an amorphous suboxide (a-HfOx), then to a crystalline, hexagonal suboxide (h-HfOx) in epitaxial relationship with the substrate, and finally to m-HfO2 that is also epitaxial. We use scanning transmission electron microscopy to characterize the epitaxial relationships and to investigate the structure of h-HfOx. We propose a series of displacive transformations that relate the different crystalline phases and are consistent with the observed epitaxial relationships with the graphene substrate. ReaxFF based reactive molecular dynamics simulations confirm our model of the oxide phase sequencing, and illustrate the role of graphene in promoting oxide crystallization. Our results suggest a way to achieve heteroepitaxial integration of high-performance, crystalline dielectrics with two dimensional (2D) semiconductors with an atomically sharp interface, which is also relevant to hafnia phase engineering.

cond-mat.mtrl-sci↗

arXiv2024

Impact of Neutron Irradiation on LGADs with a Carbon-Enriched Shallow Multiplication Layer: Degradation of Timing Performance and Gain

In this radiation tolerance study, Low Gain Avalanche Detectors (LGADs) with a carbon-enriched broad and shallow multiplication layer were examined in comparison to identical non-carbonated LGADs. Manufactured at IMB-CNM, the sensors underwent neutron irradiation at the TRIGA reactor in Ljubljana, reaching a fluence of $1.5e^{15} {n_{eq}} cm^{-2}$. The results revealed a smaller deactivation of boron and improved resistance to radiation in carbonated LGADs. The study demonstrated the potential benefits of carbon enrichment in mitigating radiation damage effects, particularly the acceptor removal mechanism, reducing the acceptor removal constant by more than a factor of two. Additionally, time resolution and collected charge degradation due to irradiation were observed, with carbonated samples exhibiting better radiation tolerance. A noise analysis focused on baseline noise and spurious pulses showed the presence of thermal-generated dark counts attributed to a too narrow distance between the gain layer end and the p-stop implant at the periphery of the pad for the characterized LGAD design; however, without significant impact of operation performance.

physics.ins-det↗

arXiv2024

A Processing Route to Chalcogenide Perovskites Alloys with Tunable Band Gap via Anion Exchange

We demonstrate synthesis of BaZr(S,Se)3 chalcogenide perovskite alloys by selenization of BaZrS3 thin films. The anion-exchange process produces films with tunable composition and band gap without changing the orthorhombic perovskite crystal structure or the film microstructure. The direct band gap is tunable between 1.5 and 1.9 eV. The alloy films made in this way feature 100x stronger photoconductive response and a lower density of extended defects, compared to alloy films made by direct growth. The perovskite structure is stable in high-selenium-content thin films with and without epitaxy. The manufacturing-compatible process of selenization in H2Se gas may spur the development of chalcogenide perovskite solar cell technology.

cond-mat.mtrl-sci↗

arXiv2024

Vibrational properties differ between halide and chalcogenide perovskite semiconductors, and it matters for optoelectronic performance

We report a comparative study of temperature-dependent photoluminescence and structural dynamics of two perovskite semiconductors, the chalcogenide BaZrS$_3$ (BZS) and the halide CsPbBr$_3$ (CPB). These materials have similar crystal structures and direct band gaps, but we find that they have quite distinct optoelectronic and vibrational properties. Both materials exhibit thermally-activated non-radiative recombination, but the non-radiative recombination rate in BZS is between two and four orders of magnitude faster than in CPB. Raman spectroscopy reveals that the effects of phonon anharmonicity are far more pronounced in CPB than in BZS. Further, although both materials feature a large dielectric response due to low-energy polar optical phonons, the phonons in CPB are substantially lower in energy than in BZS. Our results suggest that electron-phonon coupling in BZS is more effective at non-radiative recombination than in CPB, and that BZS may also have a substantially higher concentration of non-radiative recombination centers than CPB. The low defect concentration in CPB may be related to the ease of lattice reconfiguration, typified by anharmonic bonding. It remains to be seen to what extent these differences are inherent to the chalcogenide and halide perovskites and to what extent they can be affected by materials processing; comparing BZS single-crystals and thin films provides reason for optimism.

cond-mat.mtrl-sci↗

arXiv2022

Kinetic control for planar oxidation of MoS$_2$

Layered transition metal dichalcogenide (TMD) semiconductors oxidize readily in a variety of conditions, and a thorough understanding of this oxide formation is required for the advancement of TMD-based microelectronics. Here, we combine scanning transmission electron microscopy (STEM) with spectroscopic ellipsometry (SE) to investigate oxide formation at the atomic scale of the most widely-studied TMD, MoS$_2$. We find that aggressive thermal oxidation results in $\alpha$-phase plate-like crystalline MoO$_3$ with sharp interfaces, voids, and a textured alignment with the underlying MoS$_2$. Experiments with remote substrates and patterned MoS$_2$ prove that thermal oxidation proceeds via vapor-phase mass transport and redeposition - a challenge to forming thin, conformal planar oxide films. We accelerate the kinetics of oxidation relative to the kinetics of mass transport using a non-thermal oxygen plasma process, to form a smooth and conformal amorphous oxide. The resulting amorphous MoO$_3$ films can be grown several nanometers thick, and we calibrate the oxidation rate for varying plasma processing conditions. Our results illustrate how TMD semiconductor oxidation differs significantly from oxidation of legacy semiconductors, most notably silicon, and provide quantitative guidance for managing both the atomic scale structure and thin film morphology of oxides in the design and processing of MoS$_2$ semiconductor devices.

physics.app-ph↗

arXiv2022

A new semiconducting perovskite alloy system made possible by gas-source molecular beam epitaxy

Optoelectronic technologies are based on families of semiconductor alloys. It is rare that a new semiconductor alloy family is developed to the point where epitaxial growth is possible; since the 1950s, this has happened approximately once per decade. Here we demonstrate epitaxial thin film growth of semiconducting chalcogenide perovskite alloys in the Ba-Zr-S-Se system by gas-source molecular beam epitaxy (MBE). We stabilize the full range y = 0 ... 3 of compositions BaZrS$_{(3-y)}$Se$_y$ in the perovskite structure, up to and including BaZrSe$_3$, by growing on BaZrS$_3$ epitaxial templates. The resulting films are environmentally stable and the direct band gap ($E_g$) varies strongly with Se content, as predicted by theory, covering the range $E_g$ = 1.9 ... 1.4 eV for $y$ = 0 ... 3. This creates possibilities for visible and near-infrared (VIS-NIR) optoelectronics, solid state lighting, and solar cells using chalcogenide perovskites.

cond-mat.mtrl-sci↗

arXiv2022

Modeling Defect-Level Switching for Highly-Nonlinear and Hysteretic Electronic Devices

Previously, we demonstrated hysteretic and persistent changes of resistivity in two-terminal electronic devices based on charge trapping and detrapping at immobile metastable defects [H. Yin, A. Kumar, J.M. LeBeau, and R. Jaramillo, Phys. Rev. Applied 15, 014014 (2021)]; we termed these devices as defect-level switching (DLS) devices. DLS devices feature all-electronic resistive switching and thus are volatile because of the voltage-time dilemma. However, the dynamics of volatile resistive switches may be valuable for emerging applications such as selectors in crosspoint memory, and neuromorphic computing concepts. To design memory and computing circuits using these volatile resistive switches, accurate modeling is essential. In this work we develop an accurate and analytical model to describe the switching physics in DLS devices, based on the established theories of point defect metastability in Cu(In,Ga)Se2 (CIGS) and II-VI semiconductors. The analytical nature of our model allows for time-efficient simulations of dynamic behavior of DLS devices. We model the time durations of SET and RESET programming pulses, which can be exponentially shortened with respect to the pulse amplitude. We also demonstrate the concept of inverse design: given desired resistance states, the width and amplitude of the programming signal can be chosen accordingly.

cond-mat.mtrl-sci↗

arXiv2021

Test beam characterization of sensor prototypes for the CMS Barrel MIP Timing Detector

The MIP Timing Detector will provide additional timing capabilities for detection of minimum ionizing particles (MIPs) at CMS during the High Luminosity LHC era, improving event reconstruction and pileup rejection. The central portion of the detector, the Barrel Timing Layer (BTL), will be instrumented with LYSO:Ce crystals and Silicon Photomultipliers (SiPMs) providing a time resolution of about 30 ps at the beginning of operation, and degrading to 50-60 ps at the end of the detector lifetime as a result of radiation damage. In this work, we present the results obtained using a 120 GeV proton beam at the Fermilab Test Beam Facility to measure the time resolution of unirradiated sensors. A proof-of-concept of the sensor layout proposed for the barrel region of the MTD, consisting of elongated crystal bars with dimensions of about 3 x 3 x 57 mm$^3$ and with double-ended SiPM readout, is demonstrated. This design provides a robust time measurement independent of the impact point of the MIP along the crystal bar. We tested LYSO:Ce bars of different thickness (2, 3, 4 mm) with a geometry close to the reference design and coupled to SiPMs manufactured by Hamamatsu and Fondazione Bruno Kessler. The various aspects influencing the timing performance such as the crystal thickness, properties of the SiPMs (e.g. photon detection efficiency), and impact angle of the MIP are studied. A time resolution of about 28 ps is measured for MIPs crossing a 3 mm thick crystal bar, corresponding to an MPV energy deposition of 2.6 MeV, and of 22 ps for the 4.2 MeV MPV energy deposition expected in the BTL, matching the detector performance target for unirradiated devices.

physics.ins-det↗

arXiv2021

Making BaZrS3 chalcogenide perovskite thin films by molecular beam epitaxy

We demonstrate the making of BaZrS3 thin films by molecular beam epitaxy (MBE). BaZrS3 forms in the orthorhombic distorted-perovskite structure with corner-sharing ZrS6 octahedra. The single-step MBE process results in films smooth on the atomic scale, with near-perfect BaZrS3 stoichiometry and an atomically-sharp interface with the LaAlO3 substrate. The films grow epitaxially via two, competing growth modes: buffered epitaxy, with a self-assembled interface layer that relieves the epitaxial strain, and direct epitaxy, with rotated-cube-on-cube growth that accommodates the large lattice constant mismatch between the oxide and the sulfide perovskites. This work sets the stage for developing chalcogenide perovskites as a family of semiconductor alloys with properties that can be tuned with strain and composition in high-quality epitaxial thin films, as has been long-established for other systems including Si-Ge, III-Vs, and II-Vs. The methods demonstrated here also represent a revival of gas-source chalcogenide MBE.

cond-mat.mtrl-sci↗

arXiv2020

Refractive uses of layered and two-dimensional materials for integrated photonics

The scientific community has witnessed tremendous expansion of research on layered (i.e. two-dimensional, 2D) materials, with increasing recent focus on applications to photonics. Layered materials are particularly exciting for manipulating light in the confined geometry of photonic integrated circuits, where key material properties include strong and controllable light-matter interaction, and limited optical loss. Layered materials feature tunable optical properties, phases that are promising for electro-optics, and a panoply of polymorphs that suggest a rich design space for highly-nonperturbative photonic integrated devices based on phase-change functionality. All of these features are manifest in materials with band gap above the photonics-relevant near-infrared (NIR) spectral band ($\sim$ 0.5 - 1 eV), meaning that they can be harnessed in refractive (i.e. non-absorptive) applications.

cond-mat.mtrl-sci↗

arXiv2020

Discovery of highly-polarizable semiconductors BaZrS3 and Ba3Zr2S7

There are few known semiconductors exhibiting both strong optical response and large dielectric polarizability. Inorganic materials with large dielectric polarizability tend to be wide-band gap complex oxides. Semiconductors with strong photoresponse to visible and infrared light tend to be weakly polarizable. Interesting exceptions to these trends are halide perovskites and phase-change chalcogenides. Here we introduce complex chalcogenides in the Ba-Zr-S system in perovskite and Ruddlesden-Popper structures as a new family of highly polarizable semiconductors. We report the results of impedance spectroscopy on single crystals that establish BaZrS3 and Ba3Zr2S7 as semiconductors with low-frequency relative dielectric constant ($ε_0$) in the range 50 - 100, and band gap in the range 1.3 - 1.8 eV. Our electronic structure calculations indicate the enhanced dielectric response in perovskite BaZrS3 versus Ruddlesden-Popper Ba3Zr2S7 is primarily due to enhanced IR mode-effective charges, and variations in phonon frequencies along $\langle 001 \rangle$; differences in the Born effective charges and the lattice stiffness are of secondary importance. This combination of covalent bonding in crystal structures more common to complex oxides results in a sizable Fröhlich coupling constant, which suggests that charge carriers are large polarons.

cond-mat.mtrl-sci↗

arXiv2020

Defect Level Switching for Highly-Nonlinear and Hysteretic Electronic Devices

Nonlinear and hysteretic electrical devices are needed for applications from circuit protection to next-generation computing. Widely-studied devices for resistive switching are based on mass transport, such as the drift of ions in an electric field, and on collective phenomena, such as insulator-metal transitions. We ask whether the large photoconductive response known in many semiconductors can be stimulated in the dark and harnessed to design electrical devices. We design and test devices based on photoconductive CdS, and our results are consistent with the hypothesis that resistive switching arises from point defects that switch between deep- and shallow-donor configurations: defect level switching (DLS). This new electronic device design principle - photoconductivity without photons - leverages decades of research on photoconductivity and defect spectroscopy. It is easily generalized and will enable the rational design of new nonlinear, hysteretic devices for future electronics.

physics.app-ph↗

arXiv2019

Crystal growth and structural analysis of perovskite chalcogenide BaZrS$_3$ and Ruddlesden-Popper phase Ba$_3$Zr$_2$S$_7$

Perovskite chalcogenides are gaining substantial interest as an emerging class of semiconductors for optoelectronic applications. High quality samples are of vital importance to examine their inherent physical properties. We report the successful crystal growth of the model system, BaZrS$_3$ and its Ruddlesden-Popper phase Ba$_3$Zr$_2$S$_7$ by flux method. X-ray diffraction analyses showed space group of $Pnma$ with lattice constants of $a$ = 7.056(3) Å\/, $b$ = 9.962(4) Å\/, $c$ = 6.996(3) Å\/ for BaZrS$_3$ and $P4_2/mnm$ with $a$ = 7.071(2) Å\/, $b$ = 7.071(2) Å\/, $c$ = 25.418(5) Å\/ for Ba$_3$Zr$_2$S$_7$. Rocking curves with full-width-at-half-maximum of 0.011$^\circ$ for BaZrS$_3$ and 0.027$^\circ$ for Ba$_3$Zr$_2$S$_7$ were observed. Pole figure analysis, scanning transmission electron microscopy images and electron diffraction patterns also establish high quality of grown crystals. The octahedra tilting in the corner-sharing octahedra network are analyzed by extracting the torsion angles.

cond-mat.mtrl-sci↗

arXiv2019

Near-infrared optical properties and proposed phase-change usefulness of transition metal disulfides

The development of photonic integrated circuits would benefit from a wider selection of materials that can strongly-control near-infrared (NIR) light. Transition metal dichalcogenides (TMDs) have been explored extensively for visible spectrum opto-electronics, but the NIR properties of these layered materials have been less-studied. The measurement of optical constants is the foremost step to qualify TMDs for use in NIR photonics. Here we measure the complex optical constants for select sulfide TMDs (bulk crystals of MoS2, TiS2 and ZrS2) via spectroscopic ellipsometry in the visible-to-NIR range. Through Mueller matrix measurements and generalized ellipsometry, we explicitly measure the direction of the ordinary optical axis. We support our measurements with density functional theory (DFT) calculations, which agree with our measurements and predict giant birefringence. We further propose that TMDs could find use as photonic phase-change materials, by designing alloys that are thermodynamically adjacent to phase boundaries between competing crystal structures, to realize martensitic (i.e. displacive, order-order) switching.

cond-mat.mes-hall↗

arXiv2019

Inverse Low Gain Avalanche Detectors (iLGADs) for precise tracking and timing applications

Low Gain Avalanche Detector (LGAD) is the baseline sensing technology of the recently proposed Minimum Ionizing Particle (MIP) end-cap timing detectors (MTD) at the Atlas and CMS experiments. The current MTD sensor is designed as a multi-pad matrix detector delivering a poor position resolution, due to the relatively large pad area, around 1 $mm^2$; and a good timing resolution, around 20-30 ps. Besides, in his current technological incarnation, the timing resolution of the MTD LGAD sensors is severely degraded once the MIP particle hits the inter-pad region since the signal amplification is missing for this region. This limitation is named as the LGAD fill-factor problem. To overcome the fill factor problem and the poor position resolution of the MTD LGAD sensors, a p-in-p LGAD (iLGAD) was introduced. Contrary to the conventional LGAD, the iLGAD has a non-segmented deep p-well (the multiplication layer). Therefore, iLGADs should ideally present a constant gain value over all the sensitive region of the device without gain drops between the signal collecting electrodes; in other words, iLGADs should have a 100${\%}$ fill-factor by design. In this paper, tracking and timing performance of the first iLGAD prototypes is presented.

physics.ins-det↗

arXiv2018

Ideal Bandgap in a 2D Ruddlesden-Popper Perovskite Chalcogenide for Single-junction Solar Cells

Transition metal perovskite chalcogenides (TMPCs) are explored as stable, environmentally friendly semiconductors for solar energy conversion. They can be viewed as the inorganic alternatives to hybrid halide perovskites, and chalcogenide counterparts of perovskite oxides with desirable optoelectronic properties in the visible and infrared part of the electromagnetic spectrum. Past theoretical studies have predicted large absorption coefficient, desirable defect characteristics, and bulk photovoltaic effect in TMPCs. Despite recent progresses in polycrystalline synthesis and measurements of their optical properties, it is necessary to grow these materials in high crystalline quality to develop a fundamental understanding of their optical properties and evaluate their suitability for photovoltaic application. Here, we report the growth of single crystals of a two-dimensional (2D) perovskite chalcogenide, Ba3Zr2S7, with a natural superlattice-like structure of alternating double-layer perovskite blocks and single-layer rock salt structure. The material demonstrated a bright photoluminescence peak at 1.28 eV with a large external luminescence efficiency of up to 0.15%. We performed time-resolved photoluminescence spectroscopy on these crystals and obtained an effective recombination time of ~65 ns. These results clearly show that 2D Ruddlesden-Popper phases of perovskite chalcogenides are promising materials to achieve single-junction solar cells.

cond-mat.mtrl-sci↗