Room Temperature Current-voltage Characteristics Research Articles

Modulation of resistance switching in Au/Nb:SrTiO3 Schottky junctions by ambient oxygen

We investigated the room-temperature current-voltage characteristics of Au/Nb:SrTiO3 Schottky junctions under various atmospheres and working pressures. We observed that oxygen partial pressure reversibly modulates junction response, briefly individual specimens behave as high-quality rectifiers in oxygen-rich atmospheres and as bipolar resistive switches in vacuum and inert gases. A two orders of magnitude modulation of resistance switching characterizes samples with the highest content of interfacial oxygen vacancies. We attribute this behavior to oxygen ionosorption and chemical oxidation at the metal-oxide interface. Our results are relevant to oxide devices displaying resistive switching at ambient-exposed interfaces, and might be exploited for gas detection purposes.

Surface morphology and electrical properties of Au/Ni/〈C〉/n-Ga2O3/p-GaSe〈KNO3〉 hybrid structures fabricated on the basis of a layered semiconductor with nanoscale ferroelectric inclusions

Features of the formation of Au/Ni/〈C〉/n-Ga2O3 hybrid nanostructures on a Van der Waals surface (0001) of “layered semiconductor-ferroelectric” composite nanostructures (p-GaSe〈KNO3〉) are studied using atomic-force microscopy. The room-temperature current-voltage characteristics and the dependence of the impedance spectrum of hybrid structures on a bias voltage are studied. The current-voltage characteristic includes a resonance peak and a portion with negative differential resistance. The current attains a maximum at a certain bias voltage, when electric polarization switching in nanoscale three-dimensional inclusions in the layered GaSe matrix occurs. In the high-frequency region (f > 106 Hz), inductive-type impedance (a large negative capacitance of structures, ∼106 F/mm2) is detected. This effect is due to spinpolarized electron transport in a series of interconnected semiconductor composite nanostructures with multiple p-GaSe〈KNO3〉 quantum wells and a forward-biased “ferromagnetic metal-semiconductor” polarizer (Au/Ni/〈C〉/n +-Ga2O3/n-Ga2O3). A shift of the maximum (current hysteresis) is detected in the current-voltage characteristics for various directions of the variations in bias voltage.

Anomalous electron transport in back-gated field-effect transistors with TiTe2 semimetal thin-film channels

The authors report on “graphene-like” mechanical exfoliation of thin films of titanium ditelluride and investigation of their electronic properties. The exfoliated crystalline TiTe2 films were used as the channel layers in the back-gated field-effect transistors fabricated with Ti/Al/Au metal contacts on SiO2/Si substrates. The room-temperature current-voltage characteristics revealed strongly non-linear behavior with signatures of the source-drain threshold voltage similar to those observed in the charge-density-wave devices. The drain-current showed an unusual non-monotonic dependence on the gate bias characterized by the presence of multiple peaks. The obtained results can be potentially used for implementation of the non-Boolean logic gates.

Characterization of deep levels in n-type and semi-insulating 4H-SiC epitaxial layers by thermally stimulated current spectroscopy

We have investigated deep level centers in n-type and semi-insulating (SI) 4H-SiC epitaxial layers by thermally stimulated current (TSC) spectroscopy. The epitaxial layers were grown using chemical vapor deposition utilizing a dichlorosilane precursor. Both epitaxial layers exhibited relatively shallow levels related to Al, B, L- and D-centers. A deep level center with an activation energy of 1.1 eV, peaked at ∼400 K, was detected in the n-type epitaxial layer and correlated with the IL2 level and the 1.1 eV center in a high purity bulk SI 4H-SiC. The TSC spectra of the SI epitaxial layer was dominated by the peaks at 525–585 K that we attributed to intrinsic defects and their complexes with energy levels close to the middle of the bandgap. The TSC spectra of SI epitaxial layer exhibited peaks with different current polarity which is explained by thermoelectric effect and the built-in electric field reversal. The results of the transfer length method measurements of the SI epitaxial layer and the room temperature current-voltage (I-V) characteristics of both epitaxial layers are also reported.

Temperature Dependence of the Giant Magnetoresistance in Fe/DNA/Fe Structure

A numerical study is presented to investigate the spin-dependent transport through poly(dG)-poly(dC) DNA molecule sandwiched between ferromagnetic contacts in the absence and in the presence of environmental effects. Making use of tight-binding procedure and within the framework of a generalized Green's function technique, the room temperature current-voltage characteristics of DNA molecule and the giant magnetoresistance (GMR) of Electrode/DNA/Electrode structure, with iron (Fe) as the electrode are studied. It is found that the GMR to be lower than 12% for small applied bias and about 35% for applied bias larger than 2.5 volts. Considering the environmental effects, the GMR would be increased up to 13% at a bias lower than 2 volts and decreases up to 23% for the bias about 2.5 volts. In addition, our calculations indicate that for applied biases around 2.5 volts, the GMR decreases when the temperature increased.

Hydrothermal synthesis of CdTe QDs: Their luminescence quenching in the presence of bio-molecules and observation of bistable memory effect in CdTe QD/PEDOT:PSS heterostructure

We report one-pot hydrothermal synthesis of nearly mono-disperse 3-mercaptopropionic acid capped water-soluble cadmium telluride (CdTe) quantum dots (QDs) using an air stable Te source. The optical and electrical characteristics were also studied here. It was shown that the hydrothermal synthesis could be tuned to synthesize nano structures of uniform size close to nanometers. The emissions of the CdTe QDs thus synthesized were in the range of 500–700 nm by varying the duration of synthesis. The full width at half maximum (FWHM) of the emission peaks is relatively narrow (40–90 nm), which indicates a nearly uniform distribution of QD size. The structural and optical properties of the QDs were characterized by transmission electron microscopy (TEM), photoluminescence (PL) and Ultraviolet–visible (UV–Vis) spectroscopy. The photoluminescence quenching of CdTe QDs in the presence of l-cysteine and DNA confirms its biocompatibility and its utility for biosensing applications. The room temperature current–voltage characteristics of QD film on ITO coated glass substrate show an electrically induced switching between states with high and low conductivities. The phenomenon is explained on the basis of charge confinement in quantum dots.

Sensor properties of structures with porous silicon layer

We have measured at room temperature current-voltage and noise characteristics of structures with a porous silicon (porosity 80%) layer at adsorption of gases ammonia, propane and butane mixture, and ethyl alcohol vapor. It was obtained that the largest change in CVC and low-frequency noise is observed under action of ammonia gas on the structure. Physical reasons of sensor properties of studied samples are discussed.

Characterization of InGaN/GaN light-emitting diodes with micro-hole arrayed indium-tin-oxide layer

We demonstrate that InGaN/GaN multiple quantum well light-emitting diodes (LEDs) with micro-hole arrayed indium-tin-oxide layers exhibit better performance and optoelectrical properties than do conventional LEDs. Under 20 mA injection current operation the room-temperature output power conversion efficiency and external quantum efficiency obtained by employing a micro-hole array on the top surface of the LED structure could be increased by 28.7% and 14.3%, respectively, over that of conventional broad area devices. The room temperature current–voltage characteristics of the LEDs showed the series resistance and leakage current to be related to the hole dimensions and etching depth, respectively. Interestingly, the leakage current of the transparent conductive layer was dominated by the contribution of the micro-hole side-wall, the number of etched micro-holes, and the wet-etching depth. We conclude that a well-designed micro-hole array structure fabricated using the wet etching process can indeed, not only significantly inhibit the leakage current of the indium-tin-oxide transparent conductive layer, but also enhance the external quantum efficiency and extraction efficiency over a broad temperature range.

TMR and spin-dependent transport of polyacetylene-based magnetic junctions

A numerical study is presented that investigates the spin-dependent transport through a trans-polyacetylene (trans-PA) molecule sandwiched between ferromagnetic (FM) contacts. Using the tight-binding procedure and in the framework of a generalized Green's function technique, the room temperature current–voltage characteristics of the trans-PA molecule and the tunnel magnetoresistance (TMR) of the electrode/trans-PA/electrode structure, with iron (Fe) as the electrode, are studied. It is found that the parallel arrangement of magnetic moments in FM electrodes causes a much higher current through the polyacetylene molecule than does the anti-parallel arrangement. Also, our results indicate that TMR has its maximum value (more than 60%) at low bias voltages.

Si Esaki diodes with high peak to valley current ratios

We report room temperature current voltage characteristics of Si p+-i-n+ Esaki diodes integrated on silicon substrates. The diodes were fabricated by low-temperature molecular beam epitaxy. Very high and abrupt p- and n-type dopant transitions into the 1020 cm−3 ranges are achieved by boron and antimony, respectively. The integrated devices are realized without a postgrowth annealing step. The silicon Esaki diodes show negative differential resistance at room temperature with excellent peak to valley current ratios up to 3.94. A variation in the thickness of the silicon tunneling barrier changes the peak current density over three orders of magnitude.

Antimony doped Si Esaki diodes without post growth annealing

Room temperature current density versus voltage characteristics of silicon Esaki diodes grown with molecular beam epitaxy are presented. The diodes are doped with boron and antimony. The integrated devices are realized without a post growth annealing step. Good peak to valley current ratios in excess of 3 and excellent peak current densities up to 5.2 kA/cm 2 were found at room temperature. We present a detailed investigation of the influence on the boron surface segregation effects of the peak current density.

Synthesis and characterization of conducting polypyrrole-polymannuronate nanocomposites

Polypyrrole-polymannuronate (PPy-PM) composite films were studied by preparing the composites via in situ deposition techniques. These studies on the chemical interactions, structural morphology, and thermal properties of the films support the formation of PPy-PM composites, and suggest that the ratio of pyrrole to PM is tailored to optimize the potential crosslinking inside the composite. The room temperature current–voltage characteristics and the frequency-dependent AC conductivity of the PPy-PM composites were studied within the frequency range of 102 to 106 Hz. Based on the aforementioned properties, the synthesis of PPy-PM composite films may suggest the future development of biomimetic materials that can be used to create new multicomponent and multifunctional bionanocomposite materials.

Influence of Thermal Annealing on the Electrical Properties of Poly(3-hexylthiophene)-Based Thin Film Diodes

The effects of thermal annealing on the bulk transport properties of poly(3-hexylthiophene) (P3HT) were studied by analyzing room temperature current-voltage characteristics of polymer thin films sandwiched between indium tin oxide/poly[ethylene dioxythiophene]:poly[styrene sulfonate] (ITO/PEDOT:PSS) and aluminum electrodes, before and after a thermal annealing step. It was observed that annealing takes place in two steps: (1) Dedoping of the polymer of impurities such as oxygen, remnant solvent, water, leading to a decrease in the conductivity of the film, and (2) thermally induced motion of the polymer chains leading to closer packing, thus, stronger inter-chain interaction and, consequently, increase in conductivity. It was also observed that the ITO/PEDOT:PSS/P3HT hole injection barrier increases on annealing the ITO/PEDOT:PSS/P3HT/Al thin film devices. The implications of impurity dedoping and closer packing on the output characteristics of bulk heterojunction polymer-fullerene thin film solar cells are discussed.

Photoinduced crystallization and space charge limited current through Au/Se 92.7S 7.3/Au thin films

The present paper reports a study of photoinduced crystallization in thermally evaporated Se 92.7S 7.3 films. The photoinduced crystallization was achieved by shining white light (from 25 mW/cm 2 tungsten lamp) at room temperature for different exposure times up to 5.184 Ms. The analysis of X-ray diffraction (XRD) patterns indicated that the grain size ( D), the strain ( ζ) and the dislocation density ( δ) are photoaging dependent. The capacitance–voltage data confirmed that the relative permittivity of the films is equal to ∼10.31. Room temperature current density voltage characteristics of Au/Se 92.7S 7.3/Au films showed Ohmic conduction in the lower voltage range ∼<1 V, and space charge limited conductivity (SCLC) in the relatively high-voltage range. The SCLC was controlled by an exponential distribution of traps above the valence band. The temperature dependence of the current density in accordance with the theory for the exponential trap distributions allowed the calculation of some essential parameters such as; trap concentration, characteristic temperature, and the trap density.

I - V characteristics of Au∕Ni Schottky diodes on GaN with SiNx nanonetwork

Room temperature and temperature dependent current-voltage characteristics of Ni∕Au Schottky diodes fabricated on undoped GaN prepared with and without in situ SiNx nanonetwork by metal organic chemical vapor deposition have been studied. The features of the Schottky diodes depend strongly on the SiNx deposition conditions, namely, its thickness. Reduction in the point and line defect densities caused the Schottky barrier height to increase to 1.13eV for 5min SiNx deposition time as compared to 0.78eV without SiNx nanonetwork. Similarly, the breakdown voltage also improved from 76V for the reference to 250V when SiNx nanonetwork was used. With optimized SiNx nanonetwork, full width at half maximum values of (0002) and (101¯2) x-ray rocking curves improved to 217 and 211arcsec, respectively, for a 5.5μm thick layer, as compared to 252 and 405arcsec for a reference sample of the same thickness, which are comparable to literature values. The photoluminescence linewidth also reduced to 2.5meV at 15K with free excitons A and B clearly resolvable.

Epitaxial Growth of SiGe Interband Tunneling Diodes on Si(001) and on Si0.7Ge0.3 Virtual Substrates

We present room temperature current voltage characteristics from SiGe interband tunneling diodes epitaxially grown on highly resistive Si(001) substrates. In this case, a maximum peak to valley current ratio (PVCR) of 5.65 was obtained. The possible integration of a SiGe tunnel diode with a strained Si transistor lead us to investigate the growth of SiGe interband tunneling diodes on Si 0.7 Ge 0.3 virtual substrates. A careful optimization of the layer structure leads to a maximum PVCR of 1.36 at room temperature. The latter value can be further increased to 2.26 at 3.7 K. Our results demonstrate that high quality SiGe interband tunneling diodes can be realized, which is of great interest for future memory and high speed applications.

Structural and rectifying junction properties of self-assembled ZnO nanoparticles in polystyrene diblock copolymers on (1 0 0)Si substrates

The structural and electronic transport properties of self-assembled ZnO nanoparticles in polystyrene-acrylic acid, [PS] m /[PAA] n , diblock copolymer on p-type (1 0 0)Si substrates are reported for the first time. Four different block repeat unit ratios ( m/ n) of 159/63, 139/17,106/17, and 106/4, were examined in order to correlate the physical parameters (size, density) of the nanoparticles with the copolymer block lengths m and n. We established that the self-assembled ZnO nanoparticle average size increased linearly with minority block length n, while the average density decreased exponentially with majority block length m. Average size varied from 20 nm to 250 nm and average density from 3.5 × 10 7 cm −2 to 1 × 10 10 cm −2, depending on copolymer parameters. X-ray diffraction studies showed the particles to have a wurtzite crystal structure with the (1 0 0) being the dominant orientation. Room temperature current–voltage characteristics measured for an Al/ZnO-nanocomposite/Si structure exhibited rectifying junction properties and indicated the formation of Al/ZnO-nanocomposite Schottky type junction with a barrier height of 0.7 V.

Electron Transport in Self-Assembled Polymer Molecular Junctions

A molecular junction of a poly(p-phenyleneethynylene)s derivative with thioacetate end groups (TA-PPE) was fabricated by self-assembling. Nanogap electrodes made by electroplating technique was used to couple thiol end groups of TA-PPE molecules. Room temperature current-voltage characteristics of the molecular junction exhibited highly periodic, repeatable, and identical stepwise features. First-principles calculations suggest that one possibility for the equidistant step is due to the opening of different conducting channels that corresponds to the unoccupied molecular orbitals of the polymer in the junction. It is interesting to see that an 18 nm long polymer is of quantized electronic structures and behaves like a quantum transport device.

Laser Deposited Ag3SbS3 and Tl3SbS3 Nanoscale Thin Films as Potential Electric Field Sensors

ABSTRACTPhase composition and electrical properties of Ag(Tl)SbS amorphous films obtained by pulse laser deposition technology are investigated. The films deposited on crystalline NaCl and Kcl substrates are amorphous with crystalline phase inclusions. Room-temperature current voltage characteristics showed a good electro-sensitivity of the films under applied bias up to 10 V and a space-charge-limited current was registered as a principal component of the charge carrier transport.

Unterminated 4H-SiC Schottky barrier diodes with novel HfN xB y electrodes

4H-SiC Schottky barrier diodes (SBDs) were fabricated and characterized from room temperature to 573 K using HfN x B y as Schottky electrodes. The results are compared to SBDs fabricated using other electrodes that include Ni, Pt, Ti and Au. The Schottky barrier height Φ b for as-deposited HfN x B y / n−/ n+ diodes, determined from room temperature current–voltage characteristics, is 0.887 eV. This is lower than those of SBDs fabricated using other metals such as Au, where Φ b is 1.79 eV. The HfN x B y / n−/ n+ diodes studied have a much higher on-resistance R on of around 38.24 mΩ-cm 2, which is about four times that of Au/ n−/ n+ diodes, due to the higher sheet resistance of the sputtered HfN x B y electrode layer. The barrier height Φ b and ideality factor η of the HfN x B y / n−/ n+ diodes remain almost unchanged after 400 and 750 °C anneal in N 2. This suggests excellent thermal and chemical stability of HfN x B y in contact with 4H-SiC.