Temperature-dependent Electrical Measurements Research Articles

Optically Tunable Electrical Oscillations in Oxide-Based Memristors for Neuromorphic Computing.

The application of hardware-based neural networks can be enhanced by integrating sensory neurons and synapses that enable direct input from external stimuli. This work reports direct optical control of an oscillatory neuron based on volatile threshold switching in V3O5. The devices exhibit electroforming-free operation with switching parameters that can be tuned by optical illumination. Using temperature-dependent electrical measurements, conductive atomic force microscopy (C-AFM), in situ thermal imaging, and lumped element modelling, it is shown that the changes in switching parameters, including threshold and hold voltages, arise from overall conductivity increase of the oxide film due to the contribution of both photoconductive and bolometric characteristics of V3O5, which eventually affects the oscillation dynamics. Furthermore, V3O5 is identified as a new bolometric material with a temperature coefficient of resistance (TCR) as high as -4.6% K-1 at 423 K. The utility of these devicesis illustrated by demonstrating in-sensor reservoir computing with reduced computational effort and an optical encoding layer for spiking neural network (SNN), respectively, using a simulated array of devices.

Space-Confined Growth of Ultrathin P-Type GeTe Nanosheets for Broadband Photodetectors.

As p-type phase-change degenerate semiconductors, crystalline and amorphous germanium telluride (GeTe) exhibit metallic and semiconducting properties, respectively. However, the massive structural defects and strong interface scattering in amorphous GeTe films significantly reduce their performance. In this work, two-dimensional (2D) p-type GeTe nanosheets are synthesized via a specially designed space-confined chemical vapor deposition (CVD) method, with the thickness of the GeTe nanosheets reduced to 1.9nm. The space-confined CVD method improves the crystallinity of ultrathin GeTe by lowering the partial pressure of the reactant gas, resulting in GeTe nanosheets with excellent p-type semiconductor properties, such as a satisfactory on/off ratio of 105. Temperature-dependent electrical measurements demonstrate that variable-range hopping and optical-phonon-assisted hopping mechanisms dominate transport behavior at low and high temperatures, respectively. GeTe devices exhibit significantly high responsivity (6589 and 2.2 A W-1 at 633 and 980nm, respectively) and detectivity (1.67 × 1011 and 1.3 × 108 Jones at 633 and 980nm, respectively), making them feasible for broadband photodetectors in the visible to near-infrared range. Furthermore, the fabricated GeTe/WS2 diode exhibits a rectification ratio of 103 at zero gate voltage. These satisfactory p-type semiconductor properties demonstrate that ultrathin GeTe exhibits enormous potential for applications in optoelectronic interconnection circuits.

Hollow-cathode plasma deposited vanadium oxide films: Metal precursor influence on growth and material properties

Due to its different polymorphs, including vanadium pentoxide (V2O5) and vanadium dioxide (VO2), the vanadium oxide (VOX) compound is an immensely interesting material with many important applications. While atomic layer deposition (ALD) is among the possible VOX film synthesis methods, literature reports have majorly utilized thermal-ALD, which reveals as-grown amorphous VOX films. Further post-deposition annealing process is needed to crystallize these films. High-temperature crystallization indeed limits the use of low-temperature compatible materials, processes, and substrates. In this work, we report on the low-temperature crystalline VOX film growth in a hollow-cathode plasma-enhanced atomic layer deposition reactor using two different vanadium precursors, tetrakis(ethylmethylamino)vanadium and vanadium(V) oxytriisopropoxide. Oxygen plasmas were used as co-reactants at a substrate temperature of 150 °C. Along with the purpose of investing in the impact of metal precursors on VOX film growth, we also studied Ar-plasma in situ and thermal ex situ annealing to investigate possible structural enhancement and phase transformation. In situ Ar-plasma annealing was performed with 20 s, 20 SCCM Ar-plasma, while post-deposition ex situ annealing was carried out at 500 °C and 0.5 mTorr O2 pressure. In situ ellipsometry was performed to record instant film thickness variation and several ex situ characterizations were performed to extract the optical, structural, and electrical properties of the films. The outcomes of the study confirm that both metal precursors result in as-grown crystalline V2O5 films at 150 °C. On the other hand, post-deposition annealing converted the as-grown crystalline V2O5 film to VO2 film. Finally, we have also successfully confirmed the metal-to-insulator transition property of the annealed VO2 films via temperature-dependent structural and electrical measurements.

Fully printed memristors made with MoS2 and graphene water-based inks.

2-Dimensional materials (2DMs) offer an attractive solution for the realization of high density and reliable memristors, compatible with printed and flexible electronics. In this work we fabricate a fully inkjet printed MoS2-based resistive switching memory, where graphene is used as top electrode and silver is used as bottom electrode. Memristic effects are observed only after annealing of each printed component. The printed memory on silicon shows low SET/RESET voltage, short switching times (less than 0.1 s) and resistance switching ratios of 103-105, comparable or superior to the performance obtained in devices with both printed silver electrodes on rigid substrates. The same device on Kapton shows resistance switching ratios of 102-103 and remains stable at least up to 2% of strain. The memristor resistance switching is attributed to the formation of Ag conductive filaments, which can be suppressed by integrating graphene grown by chemical vapour deposition (CVD) onto the silver electrode. Temperature-dependent electrical measurements starting from 200 K show that memristic behavior appears at a temperature of ∼300 K, confirming that an energy threshold is needed to form the conductive filament. This work shows that inkjet printing is a very powerful technique for the fabrication of 2DMs-based resistive switches onto rigid and flexible substrates.

Identification of low coefficient of thermal expansion in Al23Ce4Ni6 via combinatorial sputtering of Al-Ce-Ni-Mn thin films and upscaling to bulk materials

Al100−x-y-zCexNiyMnz thin films were synthesized via combinatorial sputtering from Al, Al80Ce20, Al91Ni9, and Al93Mn7 targets. The resultant as-deposited films exhibit a continuous composition gradient of the various constituents and form a metastable solid-solution over most of the composition space. Subsequent annealing leads to the formation of the thermodynamically stable systems of Al, and α-Al11Ce3, Al8CeMn4, and Al23Ce4Ni6 intermetallics -- where the phases present and fraction depend on the composition. Temperature dependent x-ray diffraction (TDXRD) was used to determine the coefficients of thermal expansion (CTE) for each phase. The thin film Al and Al11Ce3 temperature dependent CTE values are consistent with previously reported results. The thin film Al8CeMn4 phase reveals a slight decrease in the CTE with a range from 27 × 10−6 oC−1 to 23 × 10−6 oC−1 in the temperature range 25–550 °C. The thin film Al23Ce4Ni6 phase exhibits a CTE value of ≈ 9 × 10−6 oC−1 near room temperature and increases to 14 × 10−6 oC−1 at 550 °C. To confirm the thin film results, bulk stoichiometric Al8CeMn4 and Al23Ce4Ni6 samples were prepared and measured under similar conditions. The Al8CeMn4 bulk sample confirmed the negative CTE trend observed in the thin film sample. Compared to its thin-film counterpart, the Al23Ce4Ni6 bulk sample similarly demonstrated a low CTE value near room temperature of 5 × 10−6 oC−1 and an anomalous minimum in the CTE at ≈ 75 °C, which was confirmed via temperature dependent neutron diffraction. Temperature dependent magnetic and electrical measurements were subsequently taken on Al23Ce4Ni6, and the anomalous minimum in the CTE coincided with an electronic phase transition.

Bandgap narrowing and hole self-trapping reduction in Ga2O3 by Bi2O3 alloying

Ga2O3 is an emerging material with attractive electrical properties for improving the performance of high-voltage power electronics, and it is widely accepted that engineering its band edge energies will expand its applications, especially for bipolar devices. In this work, monoclinic phase (BixGa1−x)2O3 ternary alloys are fabricated on c-plane sapphire via magnetron co-sputtering of Ga2O3 and Bi2O3. The bandgap of Ga2O3 is found to decrease from 4.97 to 4.78 eV by alloying with a Bi x-fraction of 0.04, consistent with the theoretical prediction that alloying with Bi2O3 causes the up-shift of the valence band. Concurrent temperature-resolved cathodoluminescence (CL) measurements of the Ga2O3 and (Bi0.04Ga0.96)2O3 are employed to investigate their intrinsic ultraviolet (UV) luminescence and defect-related visible bands with increasing temperature from 80 K. The CL results reveal a more rapid thermal quenching of the self-trapped hole (STH) emission with an activation energy of only 32 meV, suggesting that alloying with Bi2O3 lowers the self-trapping energy for holes. Temperature-dependent electrical measurements reveal the conductivity of the (Bi0.04Ga0.96)2O3 film is one order of magnitude lower than that of the undoped Ga2O3 counterpart; however, both possess an electrical activation energy of ∼ 26 meV, likely associated with an impurity-related shallow donor. The low electrical conductivity of (Bi0.04Ga0.96)2O3 can be attributed to the compensation of shallow donors by acceptors activated by the Bi2O3-induced upward shift of the valence band edge. The frequency-dependent conduction and ionic polarization mechanisms up to 107 Hz are found to be identical for Ga2O3 and (Bi0.04Ga0.96)2O3, indicating that the conduction in this ternary alloy does not involve the activation of Bi acceptors.

Field and Thermal Emission Limited Charge Injection in Au-C60-Graphene van der Waals Vertical Heterostructures for Organic Electronics.

Among the family of 2D materials, graphene is the ideal candidate as top or interlayer electrode for hybrid van der Waals heterostructures made of organic thin films and 2D materials due to its high conductivity and mobility and its inherent ability of forming neat interfaces without diffusing in the adjacent organic layer. Understanding the charge injection mechanism at graphene/organic semiconductor interfaces is therefore crucial to develop organic electronic devices. In particular, Gr/C60 interfaces are promising building blocks for future n-type vertical organic transistors exploiting graphene as tunneling base electrode in a two back-to-back Gr/C60 Schottky diode configuration. This work delves into the charge transport mechanism across Au/C60/Gr vertical heterostructures fabricated on Si/SiO2 using a combination of techniques commonly used in the semiconductor industry, where a resist-free CVD graphene layer functions as a top electrode. Temperature-dependent electrical measurements show that the transport mechanism is injection limited and occurs via Fowler-Nordheim tunneling at low temperature, while it is dominated by a nonideal thermionic emission at room and high temperatures, with energy barriers at room temperature of ca. 0.58 and 0.65 eV at the Gr/C60 and Au/C60 interfaces, respectively. Impedance spectroscopy confirms that the organic semiconductor is depleted, and the energy band diagram results in two electron blocking interfaces. The resulting rectifying nature of the Gr/C60 interface could be exploited in organic hot electron transistors and vertical organic permeable-base transistors.

Robust Threshold-Switching Behavior Assisted by Cu Migration in a Ferroionic CuInP2S6 Heterostructure.

The two-dimensional layered material CuInP2S6 (CIPS) has attracted significant research attention due to its nontrivial physical properties, including room-temperature ferroelectricity at the ultrathin limit and substantial ionic conductivity. Despite many efforts to control its ionic conductance and develop electronic devices, such as memristors, improving the stability of these devices remains a challenge. This work presents a highly stable threshold-switching device based on the Cu/CIPS/graphene heterostructure, achieved after a comprehensive investigation of the activation of Cu's ionic conductivity. The device exhibits exceptional threshold-switching performance, including good cycling endurance, a high on/off ratio of up to 104, low operation voltages, and an ultrasmall subthreshold swing of less than 1.8 mV/decade for the resistance-switching process. Through temperature-dependent electrical and Raman spectroscopy measurements, the stable resistive-switching mechanism is interpreted with a drifting and diffusion model of Cu ions under the electric field, rather than the conventional conducting filament mechanism. These results make the layered ferroionic CIPS material a promising candidate for information storage devices, demonstrating a compelling approach to achieving high-performance threshold-switching memristor devices.

Unveiling Charge-Transport Mechanisms in Electronic Devices Based on Defect-Engineered MoS2 Covalent Networks.

Device performance of solution-processed 2D semiconductors in printed electronics has been limited so far by structural defects and high interflake junction resistance. Covalently interconnected networks of transition metal dichalcogenides potentially represent an efficient strategy to overcome both limitations simultaneously. Yet, the charge-transport properties in such systems have not been systematically researched. Here, the charge-transport mechanisms of printed devices based on covalent MoS2 networks are unveiled via multiscale analysis, comparing the effects of aromatic versus aliphatic dithiolated linkers. Temperature-dependent electrical measurements reveal hopping as the dominant transport mechanism: aliphatic systems lead to 3D variable range hopping, unlike the nearest neighbor hopping observed for aromatic linkers. The novel analysis based on percolation theory attributes the superior performance of devices functionalized with π-conjugated molecules to the improved interflake electronic connectivity and formation of additional percolation paths, as further corroborated by density functional calculations. Valuable guidelines for harnessing the charge-transport properties in MoS2 devices based on covalent networks are provided.

The role of Pr3+, Pr3+-Y3+ and Pr3+-Y3+-Dy3+ ions substitutions on the electrical and dielectric properties of NiCo nanospinel ferrites

This study investigated the electrical and dielectric features for NiCo (Ni0.5Co0.5Fe2O4) NSFs, Pr-NiCo (Ni0.5Co0.5Pr0.1Fe1.9O4) NSFs, PrY-NiCo (Ni0.5Co0.5Pr0.1Y0.1Fe1.8O4) NSFs and PrYDy-NiCo (Ni0.5Co0.5Pr0.1Y0.1Dy0.1Fe1.7O4) NSFs have been synthesized hydrothermally. The microstructure of all compositions was characterized thru XRD, SEM, EDX, TEM and HR-TEM. XRD analyses proved the formation of cubic structure and the absence of any impurity. The cubic morphologies of all products have been confirmed by HR-TEM and SEM measurements. The chemical composition presented by EDX was matched with the predicted chemical composition. Temperature (T) and frequency (f) dependent electrical and dielectric measurements were made to evaluate ac/dc conductivities, dielectric constant/losses, and dissipation factor as well as Cole-Cole plots of impedance functions for all NiCo NSFs substituted with Pr3+, Pr3+Y3+ and Pr3+Y3+Dy3+-ions. The ac conductivity measurements confirmed that it obeyed power law rules, largely dependent on the ion substitutions in the host NiCo NSFs. The dielectric constant of NiCo NSFs leads to the usual dielectric distribution, which is strongly influenced by substituted Pr3+, Pr3+-Y3+ and Pr3+-Y3+-Dy3+ ions. Impedance analysis indicated that the conduction mechanisms in all samples were mainly due to grain-to-grain boundaries. The variation in dispersion factors with frequency, like Koop's phenomenological model, is generally attributable to the conduction mechanism in ferrites.

Passivating Graphene and Suppressing Interfacial Phonon Scattering with Mechanically Transferred Large-Area Ga2O3.

We demonstrate a large-area passivation layer for graphene by mechanical transfer of ultrathin amorphous Ga2O3 synthesized on liquid Ga metal. A comparison of temperature-dependent electrical measurements of millimeter-scale passivated and bare graphene on SiO2/Si indicates that the passivated graphene maintains its high field effect mobility desirable for applications. Surprisingly, the temperature-dependent resistivity is reduced in passivated graphene over a range of temperatures below 220 K, due to the interplay of screening of the surface optical phonon modes of the SiO2 by high-dielectric-constant Ga2O3 and the relatively high characteristic phonon frequencies of Ga2O3. Raman spectroscopy and electrical measurements indicate that Ga2O3 passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al2O3.

Vertical inhomogeneous magnetic order in FeRh film

FeRh films, known as antiferromagnetic materials at low temperatures, exhibit unexpected ferromagnetic (FM) characteristics, unlike the bulk. The detailed temperature-dependent physical properties of FeRh films were examined to elucidate the causes. Temperature-dependent magnetic and electrical measurements showed that the coexistence of antiferromagnetic and residual FM states induces thermomagnetic irreversibility (e.g., spin-glass-like behavior) and negative magnetoresistance. Polarized neutron reflectometry (PNR) revealed the presence of non-uniform FM states at the interfaces. Additional temperature-dependent PNR profile and room temperature structural and spectroscopic analyses confirmed that the bottom FM region is correlated with structural distortion. In contrast, the top FM region is temperature-dependent and originates from non-stoichiometry.

Realization of Ultra-Scaled MoS2 Vertical Diodes via Double-Side Electrodes Lamination.

Schottky diode is the fundamental building blocks for modern electronics and optoelectronics. Reducing the semiconductor layer thickness could shrink the vertical size of a Schottky diode, improving its speed and integration density. Here, we demonstrate a new approach to fabricate a Schottky diode with ultrashort physical length approaching atomic limit. By mechanically laminating prefabricated metal electrodes on both-sides of two-dimensional MoS2, the intrinsic metal-semiconductor interfaces can be well retained. As a result, we demonstrate the thinnest Schottky diode with a length of 2.6 nm and decent rectification behavior. Furthermore, with a diode length smaller than the semiconductor depletion length, the carrier transport mechanisms are investigated and explained by thickness-dependent and temperature-dependent electrical measurements. Our study not only pushes the scaling limit of a Schottky diode but also provides a general double-sided electrodes integration approach for other ultrathin vertical devices.

Charge-Density-Wave Thin-Film Devices Printed with Chemically Exfoliated 1T-TaS2 Ink.

We report on the preparation of inks containing fillers derived from quasi-two-dimensional charge-density-wave materials, their application for inkjet printing, and the evaluation of their electronic properties in printed thin-film form. The inks were prepared by liquid-phase exfoliation of CVT-grown 1T-TaS2 crystals to produce fillers with nm-scale thickness and μm-scale lateral dimensions. Exfoliated 1T-TaS2 was dispersed in a mixture of isopropyl alcohol and ethylene glycol to allow fine-tuning of filler particles thermophysical properties for inkjet printing. The temperature-dependent electrical and current fluctuation measurements of printed thin films demonstrated that the charge-density-wave properties of 1T-TaS2 are preserved after processing. The functionality of the printed thin-film devices can be defined by the nearly commensurate to the commensurate charge-density-wave phase transition of individual exfoliated 1T-TaS2 filler particles rather than by electron-hopping transport between them. The obtained results are important for the development of printed electronics with diverse functionality achieved by the incorporation of quasi-two-dimensional van der Waals quantum materials.

Metallic vs. semiconducting properties of quasi-one-dimensional tantalum selenide van der Waals nanoribbons.

We conducted a tip-enhanced Raman scattering spectroscopy (TERS) and photoluminescence (PL) study of quasi-1D TaSe3-δ nanoribbons exfoliated onto gold substrates. At a selenium deficiency of δ ∼ 0.25 (Se/Ta = 2.75), the nanoribbons exhibit a strong, broad PL peak centered around ∼920 nm (1.35 eV), suggesting their semiconducting behavior. Such nanoribbons revealed a strong TERS response under 785 nm (1.58 eV) laser excitation, allowing for their nanoscale spectroscopic imaging. Nanoribbons with a smaller selenium deficiency (Se/Ta = 2.85, δ ∼ 0.15) did not show any PL or TERS response. The confocal Raman spectra of these samples agree with the previously-reported spectra of metallic TaSe3. The differences in the optical response of the nanoribbons examined in this study suggest that even small variations in Se content can induce changes in electronic band structure, causing samples to exhibit either metallic or semiconducting character. The temperature-dependent electrical measurements of devices fabricated with both types of materials corroborate these observations. The density-functional-theory calculations revealed that substitution of an oxygen atom in a Se vacancy can result in band gap opening and thus enable the transition from a metal to a semiconductor. However, the predicted band gap is substantially smaller than that derived from the PL data. These results indicate that the properties of van der Waals materials can vary significantly depending on stoichiometry, defect types and concentration, and possibly environmental and substrate effects. In view of this finding, local probing of nanoribbon properties with TERS becomes essential to understanding such low-dimensional systems.

A Study on the Physical Properties of SmMn2O5 Multiferroics by the Doping of Transition Metals

The polycrystalline SmMn1.8B0.2O5 (B = Fe, Cr, Co, and Ni) have been synthesized by using the sol-gel auto combustion technique sintered at 9500C. The samples are characterized by X-ray diffraction at room temperature which shows that all the samples are single phase because no secondary peaks were observed in the process of fitting by JANA 2006. All materials have an orthorhombic structure with a space group of Pbam. By changing the elements of the B-site with the same proportion, the variation in the lattice parameters and volume is described briefly and compared with other RMn2O5 multiferroics. The temperature-dependent electrical measurements were performed to calculate the activation energy and Arrhenius plot which show that all materials have semiconducting nature.

Atomically thin In2O3 field-effect transistors with 1017 current on/off ratio

Recent advances have enabled the demonstration of record high-performance atomically thin n-type indium oxide (In2O3) field-effect transistors with low thermal budget suitable for back-end-of-line logic or memory applications. By using ultra-thin layers of In2O3, its degenerate carrier density is suppressed so that it can be modulated by conventional dielectric gating. These devices have high on-currents due to its high mobility and low contact resistance; meanwhile they can have exceptionally low off-currents due to its wide bandgap. For both low-power logic and memory, the off-state performance should be understood in more detail, although they are constrained by the limits of traditional measurement techniques. In this Letter, we systematically probe the off-current of ultra-thin In2O3 transistors by adopting a wide channel geometry with temperature-dependent electrical measurements and demonstrate the potential for record high current on/off ratios of 1017 on In2O3 transistors.

Printed Electronic Devices with Inks of TiS3 Quasi-One-Dimensional van der Waals Material.

We report on the fabrication and characterization of electronic devices printed with inks of quasi-one-dimensional (1D) van der Waals materials. The quasi-1D van der Waals materials are characterized by 1D motifs in their crystal structure, which allow for their exfoliation into bundles of atomic chains. The ink was prepared by the liquid-phase exfoliation of crystals of TiS3 into quasi-1D nanoribbons dispersed in a mixture of ethanol and ethylene glycol. The temperature-dependent electrical measurements indicate that the electron transport in the printed devices is dominated by the electron hopping mechanisms. The low-frequency electronic noise in the printed devices is of 1/fγ-type with γ ∼ 1 near-room temperature (f is the frequency). The abrupt changes in the temperature dependence of the noise spectral density and γ parameter can be indicative of the phase transition in individual TiS3 nanoribbons as well as modifications in the hopping transport regime. The obtained results attest to the potential of quasi-1D van der Waals materials for applications in printed electronics.

Immobilized Precursor Particle Driven Growth of Centimeter-Sized MoTe2 Monolayer.

Molybdenum ditelluride (MoTe2) has attracted ever-growing attention in recent years due to its novel characteristics in spintronics and phase-engineering, and an efficient and convenient method to achieve large-area high-quality film is an essential step toward electronic applications. However, the growth of large-area monolayer MoTe2 is challenging. Here, for the first time, we achieve the growth of a centimeter-sized monoclinic MoTe2 monolayer and manifest the mechanism of immobilized precursor particle driven growth. Microscopic characterizations reveal an obvious trend of immobilized precursor particles being consumed by the monolayer and continuing to provide a source for the growth of the monolayer. Time-of-flight secondary ion mass spectrometry verifies the attachment of hydroxide ions on the surface of the MoTe2 monolayer, thereby realizing the inhibition of crystal growth along the [001] zone axis and the continuous growth of the MoTe2 monolayer. The first-principles DFT calculations prove the mechanism of immobilized precursor particles and the absorption of hydroxide ions on the MoTe2 monolayer. The as-grown MoTe2 monolayer exhibits a surface roughness of 0.19 nm and average conductivity of 1.5 × 10-5 S/m, which prove the smoothness and uniformity of the MoTe2 monolayer. Temperature-dependent electrical measurements together with the transfer characteristic curves further demonstrate the typical semimetallic properties of monoclinic MoTe2. Our research elaborates the microscopic process of immobilized precursor particles to grow large-area MoTe2 monolayer and provides a new thinking about the growth of many other two-dimensional materials.

Semiconductor-to-metal transition in atomic layer deposition (ALD) of VO2 films using VCl4 and water

The semiconductor-to-metal transition of vanadium dioxide (VO2) films is studied using temperature-dependent Raman, optical, and electrical measurements. The VO2 films are deposited via an atomic layer deposition (ALD) process using alternate pulses of vanadium tetrachloride and H2O at 350 °C. A growth rate of 0.021 nm/cycle and a thickness of 33 nm of VO2 are obtained for all films studied. The phase of the film is determined using x-ray diffraction. The as-deposited films are amorphous and are transformed to the monoclinic phase with a post-deposition, forming gas anneal at temperatures ≥ 500 °C for 60 min. The purity of the films is determined using x-ray photoelectron spectroscopy and no evidence of residual chlorine is detected. The temperature-dependent Raman Ag mode of the monoclinic VO2 phase is observed to monotonically decrease from 25 °C to 78 °C; where no evidence of the Ag peak is observed in the film beyond 68 °C. The refractive index and extinction coefficient extracted from temperature-dependent ellipsometry confirm that, beyond 68 °C, free carriers are generated in the film. Electrical measurements performed on a fabricated p++Si/VO2/Ti/Au device show a semiconductor-to-metal transition behavior with a high resistance of 14701 ± 2284 Ω at 62 °C and a low resistance of 1064.1 ± 143 Ω at 67 °C. This work demonstrates that a halide-based ALD process provides a clean and robust approach to synthesizing high-quality VO2 films.