arXiv subjects

Antonio Di Bartolomeo

Publications and source records attributed to Antonio Di Bartolomeo.

At least 19 recordsLinked to original sources

arXiv2026

Optically Tunable Threshold Switching and Thermally Activated Transport in Planar Ag/MAPbI$_3$ Thin Single-Crystal Devices

Halide perovskites have enabled major advances in optoelectronics, extending well beyond photovoltaics. Their mixed ionic-electronic conduction, once regarded as detrimental to device stability, is increasingly viewed as a functional degree of freedom for memory and neuromorphic-inspired devices, especially when coupled to external stimuli such as light. Specifically, single crystals are attractive models because they suppress grain-boundary effects and microstructural disorder that can mask intrinsic transport and interfacial mechanisms in polycrystalline films. Here, we report the growth of thin methylammonium lead iodide (MAPbI$_3$) single crystals by a space-confined method and their integration into planar two-terminal devices with directly deposited Ag contacts. At room temperature, the devices exhibit ultra-low dark currents ($10^{-13}-10^{-12}$ A) and negligible hysteresis in the dark. Under illumination, the current increases due to photogeneration and the I-V characteristics develop a pronounced polarity-dependent hysteresis and a threshold-like transition between two conductance states. Temperature-dependent dark measurements (300-400 K) show thermionically activated, contact-influenced transport and a weakly varying normalized hysteresis metric. Together with the back-to-back Schottky-diode analysis and control devices using more inert contact materials, these results support a transport model in which Ag/perovskite interfaces play a central role and the hysteretic response is influenced by coupled interfacial and ionic processes.

cond-mat.mtrl-sci↗

arXiv2023

Manipulation of the electrical and memory properties of MoS$_2$ field-effect transistors by highly charged ion irradiation

Field-effect transistors based on molybdenum disulfide (MoS$_2$) exhibit a hysteresis in their transfer characteristics, which can be utilized to realize 2D memory devices. This hysteresis has been attributed to charge trapping due to adsorbates, or defects either in the MoS$_2$ lattice or in the underlying substrate. We fabricated MoS$_2$ field-effect transistors on SiO$_2$/Si substrates, irradiated these devices with Xe$^{30+}$ ions at a kinetic energy of 180 keV to deliberately introduce defects and studied the resulting changes of their electrical and hysteretic properties. We find clear influences of the irradiation: While the charge carrier mobility decreases linearly with increasing ion fluence (up to only 20% of its initial value) the conductivity actually increases again after an initial drop of around two orders of magnitude, likely due to the occurence of hopping transport via localized states. We also find a significantly reduced $n$-doping ($\approx$ 10$^{12}$ per cm$^{2}$) and a well-developed hysteresis after the irradiation. The hysteresis height increases with increasing ion fluence and enables us to characterize the irradiated MoS$_2$ field-effect transistor as a memory device with remarkably longer relaxation times ($\approx$ minutes) compared to previous works.

physics.app-ph↗

arXiv2021

Memory effects in black phosphorus field effect transistors

We report the fabrication and the electrical characterization of back-gated field effect transistors with black phosphorus channel. We show that the hysteresis of the transfer characteristic, due to intrinsic defects, can be exploited to realize non-volatile memories. We demonstrate that gate voltage pulses allow to trap and store charge inside the defect states, which enable memory devices with endurance over 200 cycles and retention longer than 30 minutes. We show that the use of a protective poly (methyl methacrylate) layer, positioned on top of the black phosphorus channel, does not affect the electrical properties of the device but avoids the degradation caused by the exposure to air.

cond-mat.mes-hall↗

arXiv2021

Coexistence of negative and positive photoconductivity in few-layer PtSe2 field-effect transistors

Platinum diselenide (PtSe_2) field-effect transistors with ultrathin channel regions exhibit p-type electrical conductivity that is sensitive to temperature and environmental pressure. Exposure to a supercontinuum white light source reveals that positive and negative photoconductivity coexists in the same device. The dominance of one type of photoconductivity over the other is controlled by environmental pressure. Indeed, positive photoconductivity observed in high vacuum converts to negative photoconductivity when the pressure is rised. Density functional theory calculations confirm that physisorbed oxygen molecules on the PtSe_2 surface act as acceptors. The desorption of oxygen molecules from the surface, caused by light irradiation, leads to decreased carrier concentration in the channel conductivity. The understanding of the charge transfer occurring between the physisorbed oxygen molecules and the PtSe_2 film provides an effective route for modulating the density of carriers and the optical properties of the material.

cond-mat.mtrl-sci↗

arXiv2021

Graphene-silicon device for visible and infrared photodetection

The fabrication of graphene-silicon (Gr-Si) junction inolves the formation of a parallel metal-insulator-semiconductor (MIS) structure, which is often disregarded but plays an important role in the optoelectronic properties of the device. In this work, the transfer of graphene onto a patterned n-type Si substrate, covered by $Si_3N_4$, produces a Gr-Si device in which the parallel MIS consists of a $Gr-Si_3N_4-Si$ structure surrounding the Gr-Si junction. The Gr-Si device exhibits rectifying behavior with a rectification ratio up to $10^4$. The investigation of its temperature behavior is necessary to accurately estimate the Schottky barrier height at zero bias, $ϕ_{b0}=0.24 eV$, the effective Richardson's constant, $A^*=7 \cdot 10^{-10} AK^{-2}cm^{-2}$, and the diode ideality factor n=2.66 of the Gr-Si junction. The device is operated as a photodetector in both photocurrent and photovoltage mode in the visible and infrared (IR) spectral regions. A responsivity up to 350 mA/W and external quantum efficiency (EQE) up to 75% is achieved in the 500-1200 nm wavelength range. A decrease of responsivity to 0.4 mA/W and EQE to 0.03% is observed above 1200 nm, that is in the IR region beyond the silicon optical bandgap, in which photoexcitation is driven by graphene. Finally, a model based on two back-to-back diodes, one for the Gr-Si junction. the other for the $Gr-Si_3N_4-Si$ MIS structure, is proposed to explain the electrical behavior of the Gr-Si device.

cond-mat.mes-hall↗

arXiv2020

A current-voltage model for double Schottky barrier devices

Schottky barriers are often formed at the semiconductor/metal contacts and affect the electrical behaviour of semiconductor devices. In particular, Schottky barriers have been playing a major role in the investigation of the electrical properties of mono and two-dimensional nanostructured materials, although their impact on the current-voltage characteristics has been frequently neglected or misunderstood. In this work, we propose a single equation to describe the current-voltage characteristics of two-terminal semiconductor devices with Schottky contacts. We apply the equation to numerically simulate the electrical behaviour for both ideal and non-ideal Schottky barriers. The proposed model can be used to directly estimate the Schottky barrier height and the ideality factor. We apply it to perfectly reproduce the experimental current-voltage characteristics of ultrathin molybdenum disulphide or tungsten diselenide nanosheets and tungsten disulphide nanotubes. The model constitutes a useful tool for the analysis and the extraction of relevant transport parameters in any two-terminal device with Schottky contacts.

physics.app-ph↗

arXiv2020

Gate-controlled field emission current from MoS$_2$ nanosheets

Monolayer molybdenum disulfide (MoS$_2$) nanosheets, obtained via chemical vapor deposition onto SiO$_2$/Si substrates, are exploited to fabricate field-effect transistors with n-type conduction, high on/off ratio, steep subthreshold slope and good mobility. The transistor channel conductance increases with the reducing air pressure due to oxygen and water desorption. Local field emission measurements from the edges of the MoS$_2$ nanosheets are performed in high vacuum using a tip-shaped anode. It is demonstrated that the voltage applied to the Si substrate back-gate modulates the field emission current. Such a finding, that we attribute to gate-bias lowering of the MoS$_2$ electron affinity, enables a new field-effect transistor based on field emission.

physics.app-ph↗

arXiv2020

Field emission from AlGaN nanowires with low turn-on field

We fabricate AlGaN nanowires by molecular beam epitaxy and we investigate their field emission properties by means of an experimental setup using nano-manipulated tungsten tips as electrodes, inside a scanning electron microscope. The tip-shaped anode gives access to local properties and allows collecting electrons emitted from areas as small as 1$μm^2$. The field emission characteristics are analyzed in the framework of Fowler-Nordheim theory and we find a field enhancement factor as high as $β$ = 556 and a minimum turn-on field $E_{turn-on}$ = 17 V/$μ$m for a cathode-anode separation distance d = 500 nm. We show that for increasing separation distance, $E_{turn-on}$ increases up to about 35 V/$μ$m and $β$ decreases to 100 at d = 1600 nm. We also demonstrate the time stability of the field emission current from AlGaN nanowires for several minutes. Finally, we explain the observation of modified slope of the Fowler-Nordheim plots at low fields in terms of non-homogeneous field enhancement factors due to the presence of protruding emitters.

physics.app-ph↗

arXiv2020

Isotropic conduction and negative photoconduction in ultrathin PtSe$_2$ films

PtSe$_2$ ultrathin films are used as the channel of back-gated field-effect transistors (FETs) that are investigated at different temperatures and under super-continuous white laser irradiation. The temperature-dependent behavior confirms the semiconducting nature of multilayer PtSe$_2$, with p-type conduction, a hole field-effect mobility up to 40 cm2/(Vs) and significant gate modulation. Electrical conduction measured along different directions shows isotropic transport. A reduction of PtSe$_2$ channel conductance is observed under exposure to light. Such negative photoconductivity is explained by a photogating effect caused by photo-charge accumulation in SiO$_2$ and at the Si/SiO$_2$ interface.

physics.app-ph↗

arXiv2020

Field emission from two-dimensional GeAs

GeAs is a layered material of the IV-V groups that is attracting growing attention for possible applications in electronic and optoelectronic devices. In this study, exfoliated multilayer GeAs nanoflakes are structurally characterized and used as the channel of back-gate field-effect transistors. It is shown that their gate-modulated p-type conduction is decreased by exposure to light or electron beam. Moreover, the observation of a field emission current demonstrates the suitability of GeAs nanoflakes as cold cathodes for electron emission and opens up new perspective applications of two-dimensional GeAs in vacuum electronics. Field emission occurs with a turn-on field of ~80 V/μm and attains a current density higher than 10 A/cm^2, following the general Fowler-Nordheim model with high reproducibility.

physics.app-ph↗

arXiv2020

Field emission characteristics of InSb patterned nanowires

InSb nanowire arrays with different geometrical parameters, diameter and pitch, are fabricated by top-down etching process on Si(100) substrates. Field emission properties of InSb nanowires are investigated by using a nano-manipulated tungsten probe-tip as anode inside the vacuum chamber of a scanning electron microscope. Stable field emission current is reported, with a maximum intensity extracted from a single nanowire of about 1$μA$, corresponding to a current density as high as 10$^4$ A/cm$^2$. Stability and robustness of nanowire is probed by monitoring field emission current for about three hours. By tuning the cathode-anode separation distance in the range 500nm - 1300nm, the field enhancement factor and the turn-on field exhibit a non-monotonic dependence, with a maximum enhancement $β\simeq $ 78 and a minimum turn-on field $E_{ON} \simeq$ 0.033 V/nm for a separation d =900nm. The reduction of spatial separation between nanowires and the increase of diameter cause the reduction of the field emission performance, with reduced field enhancement ($β<$ 60) and increased turn-on field ($E_{ON} \simeq $ 0.050 V/nm). Finally, finite element simulation of the electric field distribution in the system demonstrates that emission is limited to an effective area near the border of the nanowire top surface, with annular shape and maximum width of 10 nm.

cond-mat.mes-hall↗

arXiv2019

Temperature and gate effects on contact resistance and mobility in graphene transistors by TLM and Y-function methods

The metal-graphene contact resistance is one of the major limiting factors toward the technological exploitation of graphene in electronic devices and sensors. A high contact resistance can be detrimental to device performance and spoil the intrinsic great properties of graphene. In this paper, we fabricate graphene field-effect transistors with different geometries to study the contact and channel resistance as well as the carrier mobility as a function of gate voltage and temperature. We apply the transfer length method and the y-function method showing that the two approaches can complement each other to evaluate the contact resistance and prevent artifacts in the estimation of the gate-voltage dependence of the carrier mobility. We find that the gate voltage modulates the contact and the channel resistance in a similar way but does not change the carrier mobility. We also show that the raising temperature lowers the carrier mobility, has negligible effect on the contact resistance, and can induce a transition from a semiconducting to a metallic behavior of the graphene sheet resistance, depending on the applied gate voltage. Finally we show that eliminating the detrimental effects of the contact resistance on the transistor channel current almost doubles the carrier field-effect mobility and that a competitive contact resistance an be achieved by the zig-zag shaping of the Ni contact.

physics.app-ph↗

arXiv2019

Field Emission Characterization of MoS2 Nanoflowers

Nanostructured materials have wide potential applicability as field emitters due to their high aspect ratio. We hydrothermally synthesized MoS2 nanoflowers on copper foil and characterized their field emission properties, by applying a tip-anode configuration in which a tungsten tip with curvature radius down to 30-100nm has been used as the anode to measure local properties from small areas down to 1-100um2. We demonstrate that MoS2 nanoflowers can be competitive with other well-established field emitters. Indeed, we show that a stable field emission current can be measured with a turn-on field as low as 12 V um-1 and a field enhancement factor up to 880 at 600nm cathode-anode separation distance.

cond-mat.mes-hall↗

arXiv2019

Pressure-Tunable Ambipolar Conduction and Hysteresis in Ultrathin Palladium Diselenide Field Effect Transistors

A few-layer palladium diselenide (PdSe2) field effect transistor is studied under external stimuli such as electrical and optical fields, electron irradiation and gas pressure. We observe ambipolar conduction and hysteresis in the transfer curves of the PdSe2 material unprotected and as-exfoliated. We tune the ambipolar conduction and its hysteretic behavior in the air and pure nitrogen environments. The prevailing p-type transport observed at room pressure is reversibly turned into dominant n-type conduction by reducing the pressure, which can simultaneously suppress the hysteresis. The pressure control can be exploited to symmetrize and stabilize the transfer characteristic of the device as required in high-performance logic circuits. The transistor is immune from short channel effects but is affected by trap states with characteristic times in the order of minutes. The channel conductance, dramatically reduced by the electron irradiation during scanning electron microscope imaging, is restored after several minutes anneal at room temperature. The work paves the way toward the exploitation of PdSe2 in electronic devices by providing an experiment-based and deeper understanding of charge transport in PdSe2 transistors subjected to electrical stress and other external agents.

cond-mat.mes-hall↗

arXiv2018

Environmental effects on the electrical characteristics of back-gated WSe2 field effect transistors

We study the effect of polymer coating, pressure and temperature on the electrical characteristics of monolayer WSe2 back-gated transistors with quasi-ohmic Ni/Au contacts. We find that the removal of a layer of poly(methyl methacrylate) or decreasing the pressure change the device conductivity from p to n-type. We study the current-voltage characteristics as a function of the temperature and measure a gate-tunable Schottky barrier at the contacts with a height of 60 meV in flat-band condition. We report and discuss a change in the mobility and the subthreshold slope observed with increasing temperature. Finally, we estimate the trap density at the WSe2/SiO2 interface and study the spectral photoresponse of the device, achieving a responsivity of 0.5 AW^-1 at 700 nm wavelength and 0.37 mWcm^-2 optical power.

cond-mat.mes-hall↗

arXiv2018

A WSe2 vertical field emission transistor

We report the first observation of gate-controlled field emission current from a tungsten diselenide (WSe2) monolayer, synthesized by chemical-vapour deposition on SiO2/Si substrate. Ni contacted WSe2 monolayer back-gated transistors, under high vacuum, exhibit n-type conduction and drain-bias dependent transfer characteristics, which are attributed to oxygen/water desorption and drain induced Schottky barrier lowering, respectively. The gate-tuned n-type conduction enables field emission, i.e. the extraction of electrons by quantum tunnelling, even from the flat part of the WSe2 monolayers. Electron emission occurs under an electric field ~100 V μm^(-1) and exhibit good time stability. Remarkably, the field emission current can be modulated by the back-gate voltage. The first field-emission vertical transistor based on WSe2 monolayer is thus demonstrated and can pave the way to further optimize new WSe2 based devices for use in vacuum electronics.

cond-mat.mes-hall↗

arXiv2018

Asymmetric Schottky Contacts in Bilayer MoS2 Field Effect Transistors

We discuss the high-bias electrical characteristics of back-gated field-effect transistors with CVD-synthesized bilayer MoS2 channel and Ti Schottky contacts. We find that oxidized Ti contacts on MoS2 form rectifying junctions with ~0.3 to 0.5 eV Schottky barrier height. To explain the rectifying output characteristics of the transistors, we propose a model based on two slightly asymmetric back-to-back Schottky barriers, where the highest current arises from image force barrier lowering at the electrically forced junction, while the reverse current is due to Schottky-barrier limited injection at the grounded junction. The device achieves a photo responsivity greater than 2.5 AW-1 under 5 mWcm-2 white-LED light. By comparing two- and four-probe measurements, we demonstrate that the hysteresis and persistent photoconductivity exhibited by the transistor are peculiarities of the MoS2 channel rather than effects of the Ti/MoS2 interface.

cond-mat.mes-hall↗

arXiv2018

Effect of Electron Irradiation on the Transport and Field Emission Properties of Few-Layer MoS2 Field Effect Transistors

Electrical characterization of few-layer MoS2 based field effect transistors with Ti/Au electrodes is performed in the vacuum chamber of a scanning electron microscope in order to study the effects of electron beam irradiation on the transport properties of the device. A negative threshold voltage shift and a carrier mobility enhancement is observed and explained in terms of positive charges trapped in the SiO2 gate oxide, during the irradiation. The transistor channel current is increased up to three order of magnitudes after the exposure to an irradiation dose of 100e-/nm2. Finally, a complete field emission characterization of the MoS2 flake, achieving emission stability for several hours and a minimum turn-on field of about 20 V/um with a field enhancement factor of about 500 at anode-cathode distance of 1.5um, demonstrates the suitability of few-layer MoS2 as two-dimensional emitting surface for cold-cathode applications.

physics.app-ph↗