Temperature-dependent Electrical Measurements Research Articles

Study and characterization of the irreversible transformation of electrically stressed planar Ti/TiOx/Ti junctions

We investigate the properties and characteristics of planar Ti/TiOx/Ti junctions, which consist of transverse TiOx lines drawn on Ti test patterns. Junctions are elaborated by means of local anodic oxidation using atomic force microscopy. An irreversible morphological transformation occurring in a reproducible manner is observed when these planar junctions are electrically stressed under ambient atmosphere. Structural and chemical analyses based on transmission electron microscopy techniques reveal the extension of the initial amorphous TiOx into a crystalline rutile phase. This irreversible transformation is proven to vanish completely if the electrical stress occurs under vacuum atmosphere. Finally, we carry out temperature dependent electrical measurements in order to elucidate their conduction mechanism: Schottky emission above an ultra-low potential barrier is assumed to dominate under vacuum atmosphere whereas ionic conduction seems to prevail in air.

Growth and characterization of VO2/p-GaN/sapphire heterostructure with phase transition properties

High quality pure phase VO2 films were deposited on p-GaN/sapphire substrates by pulsed laser deposition (PLD). A well-defined interface with dense and uniform morphology was observed in the as-grown VO2/p-GaN/sapphire heterostructure. The X-ray photoelectron spectroscopy (XPS) analyses confirmed the valence state of vanadium (V) in VO2 films was principally composed of V4+ with trace amount of V5+, no other valence state of V was detected. Meanwhile, a distinct reversible semiconductor-to-metal (SMT) phase transition with resistance change up to nearly three orders of magnitude was observed in the temperature dependent electrical resistance measurement, which was comparable to the high quality VO2 film grown directly on sapphire substrates. Our present findings will give a deeper insight into the physical mechanism behind the exotic characteristics of VO2/p-GaN heterostructure, and further motivate research in novel devices with combined functional properties of both correlated oxide and wide bandgap nitride semiconductors.

Martensitic phase transformation of magnetron sputtered nanostructured Ni–Mn–In ferromagnetic shape memory alloy thin films

In this paper, we report the influence of film thickness on the first order martensitic phase transformation of Ni–Mn–In ferromagnetic shape memory alloy (FSMA) thin films synthesized by magnetron sputtering. The structural, magnetic, electrical and mechanical properties of these films of various thicknesses (90–655nm) were systematically investigated. XRD analyses reveal that the film exhibit austenitic phase with L21 structure at room temperature. The grain size and crystallization extent increase with increase in film thickness. The temperature dependent magnetization and electrical measurements demonstrated the absence of phase transformation in the films with lower thickness ∼90nm which could be due to small grain size of these films. For thickness greater than 153nm, the films show first order martensitic phase transition with thermal hysteresis width, which increases with further increase in film thickness. The field dependent magnetization curves also show the increase in saturation magnetization (SM). Nanoindentation studies reveal the higher values of hardness of 7.2GPa and elastic modulus of 190GPa for the film thickness of 153nm. The value of refrigeration capacity (RC) which is an important figure of merit has been found to be 155.04mJ/cm3. Maximum exchange bias of 0.0096T and large magnetic entropy change ΔSM=15.2mJ/cm3K (field 2T) at martensitic transition has been obtained for film thickness of 655nm which makes them useful for microelectromechanical systems (MEMS) applications.

Current transport mechanisms in lattice-matched Pt/Au-InAlN/GaN Schottky diodes

Lattice-matched Pt/Au-In0.17Al0.83N/GaN hetreojunction Schottky diodes with circular planar structure have been fabricated and investigated by temperature dependent electrical measurements. The forward and reverse current transport mechanisms are analyzed by fitting the experimental current-voltage characteristics of the devices with various models. The results show that (1) the forward-low-bias current is mainly due to the multiple trap-assisted tunneling, while the forward-high-bias current is governed by the thermionic emission mechanism with a significant series resistance effect; (2) the reverse leakage current under low electric fields (<6 MV/cm) is mainly carried by the Frenkel-Poole emission electrons, while at higher fields the Fowler-Nordheim tunneling mechanism dominates due to the formation of a triangular barrier.

Tuning the switching behavior of binary oxide-based resistive memory devices by inserting an ultra-thin chemically active metal nanolayer: a case study on the Ta2O5-Ta system.

The common nonpolar switching behavior of binary oxide-based resistive random access memory devices (RRAMs) has several drawbacks in future application, such as the requirements for a high forming voltage, a large reset current, and an additional access device to settle the sneak-path issue. Herein, we propose the tuning of the switching behavior of binary oxide-based RRAMs by inserting an ultra-thin chemically active metal nanolayer, and a case study on Ta2O5-Ta systems is provided. The devices are designed to be Pt/Ta2O5(5 - x/2)/Ta(x)/Ta2O5(5 - x/2)/Pt with x = 0, 2, or 4 nm. The reference devices without the Ta nanolayer exhibit an expected nonpolar switching behavior with a high forming voltage of ∼-4.5 V and a large reset current of >10 mA. In contrast, a self-compliance bipolar switching behavior with a low forming voltage of ∼-2 V and a small reset current of <1 mA is observed after inserting a 2 nm Ta nanolayer. When the Ta nanolayer is increased to 4 nm, a complementary resistive switching (CRS) behavior is found, which can effectively settle the sneak-path issue. The appearance of CRS behavior suggests that a thin Ta nanolayer of 4 nm is robust enough to act as an inner electrode. Besides, the behind switching mechanisms are thoroughly discussed with the help of a transmission electron microscope and temperature-dependent electrical measurements. All these results demonstrate the feasibility of tuning switching behavior of binary oxide-based RRAMs by inserting an ultra-thin chemically active metal nanolayer and might help to advance the commercialization of binary oxide-based RRAMs.

Defect Chemistry of the Metal Cation Defects in the p- and n-Doped SnO2 Nanocrystalline Films

Cationic interstitial and substitutional defects, which serve as a key role in shaping the material’s performance, are considered as two kinds of important defect structures in the doped SnO2. To give a clear characterization of such metal cation defects, temperature-dependent electrical conduction measurement by the high throughput screening platform of gas-sensing materials is carried out, for the first time, to perform the defect structure studies of the p-type (Li+, Cd2+, Al3+), isovalent (Ti4+), and n-type (Nb5+, W6+) doped SnO2 nanocrystalline films in the oxygen-free atmosphere. The temperature-dependent measurements indicate that subtle induced impurities are capable of evidently modifying the electrical conduction mechanism of the SnO2. In terms of the small-polaron hopping mechanism, an improved defect chemical model is proposed in which the properties of the metal cation defects are explicitly depicted. Values for the ionization energy (ΔED) of the metal cation defects and electron hopping energy (EH) in the doped SnO2 are extracted by fitting the experimental data to the defect model. These data that reflect the nature of the metal cation defects and their effects on the electronic structure of the SnO2 are first introduced here, and the validity of these data are confirmed. What’s more, the ΔED calculated here is of critical importance for understanding the defect structure of the metal dopants in the SnO2.

Growth-substrate induced performance degradation in chemically synthesized monolayer MoS2 field effect transistors

We report on the electronic transport properties of single-layer thick chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) field-effect transistors (FETs) on Si/SiO2 substrates. MoS2 has been extensively investigated for the past two years as a potential semiconductor analogue to graphene. To date, MoS2 samples prepared via mechanical exfoliation have demonstrated field-effect mobility values which are significantly higher than that of CVD-grown MoS2. In this study, we will show that the intrinsic electronic performance of CVD-grown MoS2 is equal or superior to that of exfoliated material and has been possibly masked by a combination of interfacial contamination on the growth substrate and residual tensile strain resulting from the high-temperature growth process. We are able to quantify this strain in the as-grown material using pre- and post-transfer metrology and microscopy of the same crystals. Moreover, temperature-dependent electrical measurements made on as-grown and transferred MoS2 devices following an identical fabrication process demonstrate the improvement in field-effect mobility.

Amphoteric Nature of Sn in CdS Nanowires

High-quality CdS nanowires with uniform Sn doping were synthesized using a Sn-catalyzed chemical vapor deposition method. X-ray diffraction and transmission electron microscopy demonstrate the single crystalline wurtzite structure of the CdS/Sn nanowires. Both donor and acceptor levels, which originate from the amphoteric nature of Sn in II-VI semiconductors, are identified using low-temperature microphotoluminescence. This self-compensation effect was cross examined by gate modulation and temperature-dependent electrical transport measurement. They show an overall n-type behavior with relatively low carrier concentration and low carrier mobilities. Moreover, two different donor levels due to intrinsic and extrinsic doping could be distinguished. They agree well with both the electrical and optical data.

Investigation of structural and electrical properties of vanadium substituted disordered pyrochlore-type Ho2−xVxZr2O7 nanostructure

Disordered pyrochlore system with composition Ho2−xVxZr2O7 (where x=0, 0.25, 0.50, 0.75 and 1) has been synthesized by the normal microemulsion route to examine the effect of vanadium substitution on structural and electrical properties. The prepared compounds are characterized by several techniques including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray fluorescence (ED-XRF), energy dispersive spectra (EDS), scanning electron microscopy (SEM), temperature dependent electrical and frequency dependent dielectric measurements. The XRD analysis confirms the formation of disordered pyrochlore phase with crystallite size 7–30nm while a second phase is also observed in the highly substituted materials. The increase in resistivity is attributed to the removal of low energy pathway due to cation disordering. The dielectric constant decreases due to lowering of dipole moment with substitution and its resonance behavior shifted toward higher frequencies. The electrical and dielectric measurements suggest that materials are suitable for high frequency electronic devices, such as oscillators, resonators and frequency filters.

Bi1–xSbx Alloy Nanocrystals: Colloidal Synthesis, Charge Transport, and Thermoelectric Properties

Nanostructured Bi1-xSbx alloys constitute a convenient system to study charge transport in a nanostructured narrow-gap semiconductor with promising thermoelectric properties. In this work, we developed the colloidal synthesis of monodisperse sub-10 nm Bi1-xSbx alloy nanocrystals (NCs) with controllable size and compositions. The surface chemistry of Bi1-xSbx NCs was tailored with inorganic ligands to improve the interparticle charge transport as well as to control the carrier concentration. Temperature-dependent (10-300 K) electrical measurements were performed on the Bi1-xSbx NC based pellets to investigate the effect of surface chemistry and grain size (∼10-40 nm) on their charge transport properties. The Hall effect measurements revealed that the temperature dependence of carrier mobility and concentration strongly depended on the grain size and the surface chemistry, which was different from the reported bulk behavior. At low temperatures, electron mobility in nanostructured Bi1-xSbx was directly proportional to the average grain size, while the concentration of free carriers was inversely proportional to the grain size. We propose a model explaining such behavior. Preliminary measurements of thermoelectric properties showed a ZT value comparable to those of bulk Bi1-xSbx alloys at 300 K, suggesting a potential of Bi1-xSbx NCs for low-temperature thermoelectric applications.

Structural, spectroscopic and electrical studies of nanostructured porous ZnO thin films prepared by pulsed laser deposition

ZnO thin films are grown on quartz substrates at various substrate temperatures (ranging from 573 to 973K) under an oxygen ambience of 0.02mbar by using pulsed laser ablation. Influence of substrate temperature on the structural, morphological, optical and electrical properties of the ZnO thin films are investigated. The XRD and micro-Raman spectra reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye–Scherer equation and the average size of the crystallites are found to be in the range 17–29nm. The AFM study reveals that the surface morphology of the film depends strongly on the substrate temperature. UV–Visible transmittance spectra show highly transparent nature of the films in visible region. The calculated optical band gap energy is found to be decrease with increase in substrate temperatures. The complex dielectric constant, the loss factor and the distribution of the volume and surface energy loss of the ZnO thin films prepared at different substrate temperatures are calculated. All the films are found to be highly porous in nature. The PL spectra show very strong emission in the blue region for all the films. The dc electrical resistivity of the film decreases with increase in substrate temperature. The temperature dependent electrical measurements done on the film prepared at substrate temperature 573K reveals that the electric conduction is thermally activated and the activation energy is found to be 0.03911eV which is less than the reported values for ZnO films.

Thermal Analysis of AlGaN/GaN HEMT: Measurement and Analytical Modeling Techniques

In this paper, the temperature dependent electrical measurements by employing a Quantum Focus Instrument (QFI) and analytical analysis were presented and applied to Aluminum Gallium Nitride, Gallium Nitride (AlGaN-GaN) High Electron-Mobility Transistors (HEMTs). The analytical evaluation of band bap energy, electron mobility, thermal conductivity and thermal resistance has been carried out. The electrical measurements have been done using network analyzer with infrared IR measurement technology. The results obtained on the basis of electrical measurements are compared with analytical and simulated results for the purpose of validation of our outcomes. The measured data shows a good agreement with analytical and simulated results, thereby validating our approach of AlGaN/GaN HEMT analysis.

Lithographically Patterned p-Type SbxTey Nanoribbons with Controlled Morphologies and Dimensions

Millimeter-long one-dimensional SbxTey nanoribbons with controlled composition and dimensions (down to 16 nm) were demonstrated using lithographically patterned electrodeposition at predetermined locations. The morphology of nanoribbons was tuned by applying a pulse plating technique and addition of surfactant (i.e., CTAB) in the electrolyte. Independent of geometry, the deposit Te content decreased from 69 to 51 at. % Te with an increase in the applied potential. The electrical resistivity and field effect hole mobility were strongly dependent on the composition of the nanoribbon where the lowest electrical resistivity (7.9 × 10–4 ohm m) with highest hole mobility (24.6 cm2/V s) was observed from the Sb2Te3 nanoribbon. The temperature-dependent electrical resistance measurement shows low-temperature phase transition behaviors in the temperatures between 333 and 351 K.

Variable Range Hopping in Single-Wall Carbon Nanotube Thin Films: A Processing–Structure–Property Relationship Study

By varying the ultrasonication and ultracentrifugation conditions, single-walled carbon nanotube (SWCNT) dispersions with a broad range of SWCNT length and diameter (L = 342-3330 nm; d = 0.5-12 nm) were prepared and characterized by a preparative ultracentrifuge method (PUM) and dynamic light scattering (DLS) technique. The well-characterized dispersions were then fabricated into SWCNT thin films by spray coating. Combined optical, spectroscopic, and temperature-dependent electrical measurements were performed to study the effect of SWCNT structures on the charge transport behavior of SWCNT thin films. Regardless of SWCNT size in the dispersion and the thin film thickness, the three-dimensional variable range hopping (3D VRH) conduction model was found to be appropriate in explaining the temperature-dependent sheet resistance results for all SWCNT thin films prepared in this study. More importantly, with the SWCNT structural information determined by the PUM method, we were able to identify a strong correlation between the length of SWCNTs and the 3D VRH parameter T0, the Mott characteristic temperature. When the SWCNT length is less than ∼700 nm, the T0 of SWCNT thin films shows a drastic increase, but when the length is greater than ~700 nm, T0 is only weakly dependent on the SWCNT length. Under the framework of traditional VRH, we further conclude that the electron localization length of SWCNT thin films shows a similar dependence on the SWCNT length.

Two-stage processes of electrically induced-ferroelectric to relaxor transition in 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO3

The stability of electrically induced long-range ferroelectric order in a relaxor 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO3 ceramic material has been investigated by temperature-dependent X-ray diffraction and electrical property measurements. The depolarization and ferroelectric-to-relaxor transition are identified as separate and discrete processes. It is observed that the induced ferroelectric domains first lose their ferroelectric/ferroelastic texture coincident with a peak signal in the thermally induced depolarization current. With further increase in temperature, the detextured ferroelectric domains are dissociated into nanoscale entities. This fragmentation marks the ferroelectric-to-relaxor transition. It is suggested that the ferroelectric-to-relaxor transition has features of a second order phase transition.

Synthesis, structure and electrical properties of a new tin vanadium selenide

Abstract The turbostratically disordered misfit layer compound (SnSe) 1.15 VSe 2 was synthesized and structurally characterized. Electrical transport measurements suggest this compound undergoes a charge or spin density wave (CDW or SDW) transition, which has not been observed in previous misfit layer compounds. The (SnSe) 1.15 VSe 2 compound, created through the modulated elemental reactants technique, contains highly oriented intergrowths of SnSe bilayers and VSe 2 structured Se–V–Se trilayers with abrupt interfaces between them perpendicular to the c -axis. X-ray diffraction data and transmission electron microscope images show that each constituent has in-plane crystallinity but that there is a random rotational disorder between the constituent layers. Temperature-dependent electrical resistivity data and Hall measurements are consistent with (SnSe) 1.15 VSe 2 being a metal, however an abrupt increase in the resistivity occurs between 30 and 100 K. The carrier concentration decreases by approximately 1 carrier per vanadium atom during this temperature interval.

Temperature dependent electrical impedance spectroscopy measurements of plasma enhanced chemical vapour deposited linalyl acetate thin films

Electrical impedance spectroscopy measurements were performed on metal–insulator–metal structures using recently developed plasma deposited thin films of linalyl acetate as the insulating layer between frequencies of 10Hz and 100kHz in order to better understand this material's dielectric and structural properties. Furthermore, measurements were performed on samples fabricated under various input energy conditions to determine whether effects induced by these conditions influence the dielectric properties. The plasma deposited linalyl acetate thin films were found to be low dielectric constant across a wide range of frequencies, with primary contributions from electronic factors. Neither α- nor β-relaxation peaks were observed in the frequency range investigated at room temperature and no significant dependence of dielectric properties on input energy was observed. Samples were then investigated under heated conditions at four temperatures, where a single relaxation peak was found. This peak was quite broad, indicative of the contribution of multiple relaxations to the dielectric response. The distribution of these relaxation times was determined through regularisation methods. The breakdown field was investigated for samples at three thicknesses, and found to be approximately 1.8MV/cm.

Electronic Properties of Microscale Reduced Graphene Oxide Patterned by Micromolding

Highly uniform reduced graphene oxide (rGO) array patterns with both stripe and square shapes have been fabricated on various substrates using PDMS based soft lithography. Morphology, structure and electrical properties of the GO patterns before and after annealing at 800 °C in H2 atmosphere were investigated. The conductivity and carriers mobilities of the rGO patterns were improved by four orders after H2-reduction. Temperature-dependent electrical measurements showed that charge transport occurs via a variable range hopping mechanism.

Growth and characterization of Ba(Cd1/3Ta2/3)O3 thin films

We have synthesized stoichiometric Ba(Cd1/3Ta2/3)O3 [BCT] (100) dielectric thin films on MgO (100) substrates using Pulsed Laser Deposition. Over 99% of the BCT film was found to be epitaxial [BCT (100) || MgO (100) and BCT (010) || MgO (010)] when grown with an elevated substrate temperature of 635°C, an enhanced oxygen pressure of 53Pa and a Cd-enriched BCT target with a 1mol BCT: 1.5mol CdO composition. A dielectric constant of 32 was inferred from low-frequency capacitance measurements of a planar interdigital metal pattern. Analysis of ultra violet optical absorption results indicates that BCT has a bandgap of 4.9eV; while the interference pattern in the visible range is consistent with a refractive index of 2.1. Temperature-dependent electrical measurements indicate that the BCT films have a room temperature conductivity of 3×10−12Ω−1cm−1 with a thermal activation energy of 0.7eV. A mean particle size of ~100nm and a root mean square surface roughness of 5 to 6nm were measured using Atomic Force Microscopy.

Field-Effect Transistors Based on Thermally Treated Electron Beam-Induced Carbonaceous Patterns

Electron beam-induced carbonaceous deposition (EBICD) derived from residual hydrocarbons in the vacuum chamber has many fascinating properties. It is known to be chemically complex but robust, structurally amorphous, and electrically insulating. The present study is an attempt to gain more insight into its chemical and electrical nature based on detailed measurements such as Raman, XPS, TEM, and electrical. Interestingly, EBIC patterns are found to be blue fluorescent when excited with UV radiation, a property which owes much to sp(2) carbon clusters amidst sp(3) matrix. Temperature-dependent Raman and electrical measurements have confirmed the graphitization of the EBICD through the decomposition of functional groups above 300 °C. Finally, graphitized EBIC patterns have been employed as active p-type channel material in the field-effect transistors to obtain mobilities in the range of 0.2-4 cm(2)/V s.