Charge Limited Current Conduction Mechanism Research Articles

Forming-free resistive switching in ferroelectric Bi 0.97 Y 0.03 Fe 0.95 Sc 0.05 O 3 film for RRAM application

Electromechanical and resistive switching properties were investigated in ferroelectric rhombohedral Bi 0.97 Y 0.03 Fe 0.95 Sc 0.05 O 3 (BYFSO) film, grown on fluorine-doped tin oxide coated glass substrate. Piezoforce microscopy images of the BYFSO film after the electrical writing indicates the ferroelectric domains were switched completely towards the upward and downward direction at ± 8 V DC bias voltage, which is analogous to the ferroelectric hysteresis curve. The resistive switching effect was investigated on the Ag/BYFSO/FTO RRAM device configuration through conventional I − V characteristics. The charge transport process in Ag/BYFSO/FTO resistive device is transformed from Ohmic to space charge limited current conduction mechanism. The endurance characteristics ensure a stable bipolar resistive switching effect with a large memory window of OFF/ON ratio about ∼100 for 50 repeatable testing cycles. From the impedance spectroscopy analysis, it is observed that the bulk resistance plays a significant role during the SET-RESET process, by large degradation of resistance from megaohm (high resistance state) to kiloohm (low resistance state). The oxygen vacancy induced conductive filaments are responsible for achieving the various resistive states in the device.

Analysis of rectifying metal-semiconductor interface using impedance spectroscopy at low temperatures

This study presents the comprehensive characterization of rectifying Schottky diodes by current-voltage and impedance measurements, with the prime objective to analyze the bias and temperature dependence of impedance spectra of the fabricated diodes. For that, the impedance of the Ni/p-Si/Al Schottky diodes has been measured at various forward and reverse bias varied from +1.2 to −5.0 V, the frequency range of 1 kHz–10 MHz and in a wide temperature range of 290–100 K. In the measured bias, frequency and temperature range impedance spectra of the diode i.e. Nyquist or Cole-Cole plots follow the Debye type model with a single characteristic frequency which provides more insight into the Ni/p-Si interface. The interface or junction resistance of Ni/p-Si shows a negative temperature coefficient and peaking like behavior with bias which reveals the presence of space charge limited current conduction mechanism in the diode. While using interface capacitance of Ni/p-Si, the built-in potential (Vbi) was estimated to be 0.49 eV using the Mott-Schottky plot for the fabricated diodes. From the temperature dependent impedance characteristics of Ni/p-Si/Al Schottky diode, the dynamics of the relaxation time was studied using Arrhenius relation and energy related to the charge carriers hopping was estimated.

Gallium nitride nanocrystal formation in Si3N4 matrix by ion synthesis

Synthesis of nanoparticles in insulators attracts tremendous attention due to their unique electrical and optical properties. Here, the gallium (Ga) and gallium nitride (GaN) nanoclusters have been synthesized in the silicon nitride matrix by sequential ion implantation (gallium and nitrogen ions) followed by either furnace annealing (FA) or rapid thermal annealing (RTA). The presence of Ga and GaN nanoclusters has been confirmed by Fourier-transform infrared, Raman and X-ray photoelectron spectroscopy. Thereafter, the effect of RTA and FA on the conduction of charge carriers has been studied for the fabricated devices. It is found from the current–voltage measurements that the carrier transport is controlled by the space charge limited current conduction mechanism, and the observed values of parameter m (trap density and the distribution of localized state) for the FA and RTA devices are ~2 and ~4.1, respectively. This reveals that more defects are formed in the RTA device and that FA provides better performance than RTA from the viewpoint of opto- and nano-electronic applications.

Resistive switching characteristics and resistive switching mechanism of Au/TiO2/FTO memristor

Resistance random access memory is regarded as one of the most promising candidates for the future nonvolatile memory applications due to its good endurance, high storage density, fast erase speed and low power consumption. As one of the most important transition-metal oxides, the anatase TiO2 has received intense attention due to its inexpensive cost, strong optical absorption, favorable band edge positions and superior chemical stability. In the last decade, the nanometer-sized TiO2 has been shown to exhibit a wide range of electrical and optical properties, such as nanoscale electronics and optoelectronics, which rely mainly on the unique size and shape. Recently, various anatase TiO2 based devices such as the anatase TiO2 nanotube based memristor and the anatase TiO2 nano-film based memristor have been intensively studied due to their nonvolatile resistive switching performances. Furthermore, many conduction mechanisms have been used to elucidate the resistive switching behaviors of the anatase TiO2 based devices. However, the direct growth of anatase TiO2 nanowire arrays (NWAs) on the FTO substrate is still a challenge since there exists a large lattice mismatch of about 19% between the anatase TiO2 NWAs and the FTO substrate. Moreover, the Au/TiO2/FTO based device has not been reported and the resistive switching mechanism of the anatase TiO2 NWAs based memristor is still unclear. In this work, the anatase TiO2 NWAs with (101) preferred orientation are successfully grown on the FTO substrate by a facile one-step hydrothermal process. The resistive switching characteristics and resistive switching mechanism of the as-fabricated Au/TiO2/FTO memristor are investigated systemically. The result indicates that the Au/TiO2/FTO memristor exhibits nonvolatile bipolar resistive switching behavior. Meanwhile, the resistance ratio between high resistance state and low resistance state exceeds 20 at 0.1 V, which can be maintained over 103 s without significant degradation. In addition, the conduction mechanism of the low resistance state is governed by the ohmic conduction mechanism, while the trap-controlled space charge limited current conduction mechanism dominates the high resistance state. The resistive switching model of the Au/TiO2/FTO memristor is developed, and the resistive switching mechanism could be attributed to the formation and rupture of the conductive filaments relating to the localized oxygen vacancies. It demonstrates that the Au/TiO2/FTO memristor may be a potential candidate for the future nonvolatile memory applications.

DC conduction and breakdown behavior of thermally sprayed ceramic coatings

In this study, the DC conductivity from low electric fields up to breakdown fields is studied for several different thermally sprayed ceramic coatings. Although the DC conductivity of bulk alumina ceramic has been observed to follow the space charge limited current conduction mechanism, the studied ceramic coatings do not follow or follow only partly this mechanism. Possible reason for this is their different microstructure since bulk alumina exhibits fully crystalline microstructure while the ceramic coating consists of crystalline and amorphous regions as well as voids, defects and numerous interfaces. A possible conduction mechanism of the ceramic coatings based on the different conductivities of the amorphous and crystalline regions of the coatings is proposed. The microstructural features (e.g. volumetric porosity) are found to affect the breakdown strength for some of the studied coatings. The step-test breakdown strengths of the coatings were lower than the ramp-test ones due to the longer stress durations in step tests giving an indication of effects of electrical stress duration and possible short-term degradation of the coatings.

Hydrothermal synthesis and memristive switching behaviors of single-crystalline anatase TiO2 nanowire arrays

A facile one-step hydrothermal method has been reported to prepare the single-crystalline anatase TiO2 nanowire arrays with (101) preferentially oriented on the FTO substrate. The as-prepared Au/TiO2 NWAs/FTO based device exhibits the nonvolatile bipolar memristive switching behaviors with a high HRS/LRS resistance ratio of about three orders of magnitude. The memristive switching behaviors of the device have been elucidated by the Ohmic conduction mechanism and the trap-controlled space charge limited current conduction mechanism. Furthermore, the Schottky barriers modulated by the oxygen vacancies at the Au/TiO2 interface have been suggested to dominate the bipolar memristive switching behaviors of the device. This work demonstrates that the Au/TiO2 NWAs/FTO based device may be a promising candidate for memristor applications.

A facile hydrothermal synthesis and memristive switching performance of rutile TiO2 nanowire arrays

A facile one-step hydrothermal method has been reported to prepare the single crystalline rutile TiO2 nanowire arrays with (101) preferred orientation on the FTO substrate at a low temperature of 120 °C for 4 h. The as-prepared Au/TiO2 NWAs/FTO based device indicates a nonvolatile bipolar memristive switching behavior. The current ratio between low-resistance state and high-resistance state exceeds two orders of magnitude at −0.5 V. The memristive switching behaviors of the device have been elucidated by the Ohmic conduction mechanism and the trap-controlled space charge limited current conduction mechanism. Furthermore, the Schottky barriers modulated by the oxygen vacancies at the Au/TiO2 interface have been suggested to dominate the bias voltages-controlled bipolar memristive switching behaviors of the device. This work indicates that the Au/TiO2 NWAs/FTO based device may be a promising candidate for the memristor applications.

Electrical and photovoltaic characteristics of indium phthalocyanine chloride/p-Si solar cell

Hybrid (organic/inorganic) heterojunction solar cell based on indium phthalocyanine chloride derivative (InPcCl-D) deposited by thermal evaporation technique onto p-type silicon single crystal wafer has been fabricated. The cell was characterized by current–voltage and capacitance–voltage measurements. The dark current–voltage characteristics of Au/InPcCl-D/p-Si/Al heterojunction device were measured at different temperatures. The device showed rectification behavior with a rectification ratio of 102 at ±1V determined at room temperature. The dominant conduction mechanisms operating consequently are the thermionic emission and the single-trap space-charge limited current. The junction parameters such as diode ideality factor, potential barrier height and series resistance are estimated as a function of temperature. The device is non ideal in showing ideality factor of 3.28 at room temperature. The temperature dependence of the ideality factor, barrier height and series resistance indicates the formation of non homogenous barrier height in the junction. The space charge limited current conduction mechanism showed that the trap concentration is 1.53×1025m−3 and it lies at 0.11eV above the valence band edge. Capacitance–voltage measurements showed the abrupt nature of the junction and the built-in potential is determined. The value of the built in potential and carrier concentration are estimated as 0.85V and 3.31×1022m−3, respectively. Under illumination intensity of 100W/m2, the device showed photovoltaic behavior with open circuit voltage, Voc, and short circuit current density, Jsc, of 0.352V and 7.6mA/cm2, respectively. The values of filling factor, FF, and photo-electrical conversion efficiency, η, are estimated as 0.31 and 2.96%, respectively.

Deep energy levels and photoelectrical properties of thin cuprous oxide films

Thin films of cuprous oxide have been electrodeposited on molybdenum substrates. Some preliminary photoelectrical properties of two devices with semitransparent aluminum and gold top-electrodes have been measured. The device with a gold top-electrode exhibits a weak photovoltaic effect and a space charge limited current conduction mechanism in dark. The other device which had been annealed before the deposition of the aluminum top-electrode, exhibits a three-fold increase in resistivity and a marked difference in its temperature dependence of conductivity. From the temperature dependence of conductivity, two activation energies of 0.09 and 0.87 eV could be measured compared to 0.11 and 0.26 eV for the device with a gold electrode. Photoinduced current transient spectroscopy with a novel approach to the post-capture data analysis (additive double gate analysis) has been used in detection and the measurements of the parameters of several deep energy levels. These levels have activation energies in the range of 0.12 to 0.63 eV and capture cross-sections in the range of 10 −22 to 10 −12 cm 2. Using the role of the sample bias polarity on the identification of the type of the traps, one electron trap (surface state) and one hole trap (bulk state) could be identified among the five detected deep levels.