Space Charge Limited Current Mechanism Research Articles

Resistive switching, endurance and retention properties of ZnO/HfO2 bilayer heterostructure memory device

This work reports the fabrication of resistive memory device with a bilayer ZnO/HfO2 structure. Highly stable and uniform bipolar resistance switching (RS) characteristics were attained when HfO2 interfacial layer is introduced in ZnO device. The bilayer device attains good resistive switching with increased resistance ON-OFF ratio of the order of ∼102, better dc endurance of > 102 cycles and retention of >104 s at room temperature. X-ray Photoelectron Spectroscopy (XPS) investigation is also done and it is confirmed that oxygen vacancies in ZnO thin film are responsible for improved resistance switching. The current-voltage (I–V) relationship reveals that switching behavior of these devices is mainly dominated by Space-Charge-Limited-Current mechanism (SCLC) regulated due to localized oxygen vacancies. Effect of temperature on the electrical conductivity has also been investigated to analyze the behavior of Low Resistance States (LRS) and High Resistance States (HRS). The findings imply that the bilayer ZnO/HfO2 device structure is a promising one for upcoming non-volatile memory applications.

Resistive switching behavior of the memristor based on WS2 nanosheets and polyvinylpyrrolidone nanocomposites

Ag/tungsten disulfide (WS2)–polyvinylpyrrolidone (PVP)/Cu memristors based on monolayer WS2 nanosheets and polyvinylpyrrolidone (PVP) nanocomposites were fabricated, and the influence of PVP content on the switching behaviors was investigated. The results indicate that the WS2–PVP based memristors show write-once read-many times (WORM) memory behavior. Remarkable resistive switching results such as a low operating voltage (VSET < 1 V), a high switching ratio (>103), good endurance (>100 cycles), and data retention time (>200 s) are obtained. With the increase in the PVP content, the device VSET gradually increases, and the switching ratio first slightly increases and then remarkably decreases. The double logarithm I–V curves verify that the switching mechanism of the devices is the trap-controlled space charge limited current mechanism, which is explained with the energy band diagram.

Facilitation of compliance current for resistive switching and stability of Ta/BaTiO<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub>/ITO

In this work, Ta/BaTiO<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> multi-layer thin film is deposited on indium tin oxide substrates by using the magnetron sputtering technology. Obvious resistive switching performance can be observed by increasing the compliance current. Ohmic and space charge limited current conduction mechanisms are demonstrated in Ta/BaTiO<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub>. The reproducible and stable resistive switching behaviors in Ta/BaTiO<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub>/ITO device at <i> I</i><sub>cc</sub> = 10<sup>–2</sup> A are reported. The results show that no obvious degradation is found after 365 successive cycles tests.

Electron Transport Mechanisms in Polyethylene Terephthalate Membranes

This paper describes carrier transport mechanisms in polyethylene terephthalate (PET) films and porous PET-based membranes (PMs) obtained by irradiating pristine PET film with swift heavy ions, with subsequent chemical etching in an alkali (NaOH) solution. The obtained PMs had through nanochannels (pores) with an average diameter of 720-750 nm. We observed that in the temperature range 240-300 K, the current-voltage characteristics I(V) of the initial Cu|PET|Cu structure obeyed the improved Mott--Gurney law, which is based on the Mark--Helfrich model for a space-charge-limited current (SCLC) mechanism for electron transport. It was found for the first time that creation of nanochannels in PMs resulted in a significant increase in the electric current density (by about three orders of magnitude) while maintaining the SCLC mechanism. The enhanced current density is explained by the formation of a highly conductive layer along the inner surface of the walls of the nanochannel that are covered with carboxyl end groups, which are created by alkaline hydrolysis. According to the model, the surface states formed by these groups enable the drift of additional electrons injected from the copper electrodes under the action of the bias voltage. Keywords: polyethylene terephthalate, electron transport, space-charge-limited current mechanism, Mark--Helfrich injection model.

Sonochemical synthesis of Fe-doped Cu3Se2 nanoparticles: Correlation of the strain and electrical properties for optoelectronics applications

This research presents the effect of different concentrations of iron (Fe) as dopants on the physical properties of the copper selenide (Cu3Se2) nanoparticle (NPs). The physical properties of the Cu3Se2 NPs were investigated using structural, morphological, and optical analysis. The results revealed that the Fe concentrations change the crystallite size (from ∼8 to 44 nm) and strain (from ∼0.0007 to 0.0030). Fe-doped Cu3Se2 NPs showed a higher optical energy band gap in comparison to the un-doped sample (1.80 eV). The films prepared by green binder (ethyl cellulose) indicated that the sample with minimum Fe concentration presents the highest carrier concentration (9.56e+18 cm−3) and lowest ideality factor (2.02) amounts. The electrical study shows space charge limited current (SCLC) mechanism in Fe-doped Cu3Se2 NPs that is not observed in un-doped sample. Using this mechanism, the highest carrier mobility (16.22 cm+2V−1s−1) obtained for sample with the lowest amount of Fe concentrations.

Variation of leakage current conduction mechanism by heat treatment in Bi-based lead-free piezoelectric ceramics

The leakage current mechanism in the as-sintered and quenched 0.75BiFeO3–0.25BaTiO3 (0.75BF–0.25BT) ceramics is evaluated by the space-charge-limited current (SCLC), Poole–Frenkel (P–F) emission, Schottky (ST) emission, and Fowler–Nordheim (F–N) tunneling mechanism. The discrepancy observed in the optical dielectric constant of BF and BT between the reported value and the values calculated from the P–F and ST emission plots suggests that the P–F emission and ST emission mechanisms do not contribute to the leakage current behavior of the 0.75BF–0.25BT ceramics. Subsequently, F–N tunneling is observed under a high electric field in the as-sintered 0.75BF–0.25BT ceramics, whereas the direct tunneling effect is exhibited throughout the measured electric field in the quenched ceramics. The SCLC mechanism is dominant in both the as-sintered and quenched 0.75BF–0.25BT ceramics. A change from Ohmic conduction to trap-filled-limit conduction is observed with an increase in the applied electric field in the as-sintered ceramics, whereas the quenched ceramics only revealed Ohmic conduction over the entire range of the measured electric field. The different behaviors exhibited in the SCLC mechanism between the as-sintered and the quenched ceramics imply that the conduction mechanism can be controlled by heat treatment.

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.

Electrochemical and electrical response of bismuth-aniline complex under the exposure of organic and inorganic environment

In this report, a simple complexation strategy has been adopted for the fabrication of bismuth-aniline based inorganic-organic hybrid system (BAC). The microscopic, optical and surface properties of the hybrid material were derived by using different analytical techniques. The synthesized material was applied as an electrocatalyst for the oxidation of iodide ion and also exhibited as a potential catalyst for the electrochemical recognition of dopamine. The device made with BAC displayed resistive switching behaviour under the exposure of iodine vapour and followed the Schottky, ohmic, space-charge and trapped-charge limited current mechanism at different voltage regions.

Aminobenzene stabilized bismuth halide nanoparticles with O-shaped hysteresis behaviour

A single pot synthesis method of aminobenzene stabilized bismuth iodide particles (ABBI) is reported for the nonvolatile random access memory application. The microscopic and surface property of the as-synthesized organic-inorganic hybrid system has been characterized using different techniques. The current-voltage characteristic of the device, made with ABBI, exhibited O-shaped hysteresis behaviour. For the random access memory application, the device was demonstrated the steady endurance and retention for 103 times and 2×103 sec, respectively. The charge transport property of the device was followed by space charge limited current and trapped assisted tunneling mechanism.

Resistive switching in Al2O3 based trilayer structure with varying parameters via experimentation and computation

Resistive switching characteristics in Al (40 nm)/Al2O3 (x nm)/Ni (50 nm) were analyzed while the middle layer thickness is varied from 5 nm to 20 nm with an increment of 5 nm each. Al/Al2O3/Ni with a total thickness of 100 nm showed the most prominent results. The current compliance was 100 mA while the voltage range for each design varied in the range of ±4 V, showing bipolar resistive switching. The double logarithmic curves indicated the presence of the Ohmic conduction and space-charge limited current mechanism. Moreover, density functional theory based calculations were performed for aluminum oxide with induced oxygen vacancy defects. The structures with oxygen vacancies showed that the nature of aluminum oxide was converted to semi-conducting from insulating, i.e., the bandgap was decreased from ∼6 eV to ∼0.6 eV. Density of states displayed that the atoms neighboring the oxygen vacant sites are responsible for a shift in states toward the valence band and Fermi level. Formation of a conduction filament (CF) is found essential for conduction in resistive random access memory (RRAM), and the computational analysis clarified that induction of oxygen vacancies is vital for the formation of CF. Finally, this work presents a detailed discussion and understanding of resistive switching in aluminum oxide-based RRAM, which is significant in the advancement of non-volatile data storage application.

CdS/Si nanofilm heterojunctions based on amorphous silicon films: Fabrication, structures, and electrical properties* *Project supported by the Natural Science Foundation of Henan Province, China (Grant No. 202300410304) and the Key Research Project for Science and Technology of the Education Department of Henan Province, China (Grant No. 21A140021).

Shortening the distance between the depletion region and the electrodes to reduce the trapped probability of carriers is a useful approach for improving the performance of heterojunction. The CdS/Si nanofilm heterojunctions are fabricated by using the radio frequency magnetron sputtering method to deposit the amorphous silicon nanofilms and CdS nanofilms on the ITO glass in turn. The relation of current density to applied voltage (I–V) shows the obvious rectification effect. From the analysis of the double logarithm I–V curve it follows that below ∼ 2.73 V the electron behaviors obey the Ohmic mechanism and above ∼ 2.73 V the electron behaviors conform to the space charge limited current (SCLC) mechanism. In the SCLC region part of the traps between the Fermi level and conduction band are occupied, and with the increase of voltage most of the traps are occupied. It is believed that CdS/Si nanofilm heterojunction is a potential candidate in the field of nano electronic and optoelectronic devices by optimizing its fabricating procedure.

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.

Corrections to “Electronic Conduction Mechanisms in Insulators” [Jan 18 223-230

In the above article, space-charge-limited current (SCLC) was modeled as involving an exponential trap distribution associated with the existence of conduction band tail states. This is no longer believed to be a viable SCLC mechanism; the poor quality of the insulators exhibiting SCLC makes it highly unlikely that the electron quasi-Fermi level can ever be modulated close enough to the conduction band edge that band tail states play any role in establishing SCLC. Instead, SCLC is now being ascribed to a Gaussian distribution of deep traps.

Electrospun 1D f-MWCNTs-TiO2 composite nanofibers for resistive memory and synaptic learning applications

Herein, we have fabricated 1-dimensional (1D) functionalized multi-walled carbon nanotubes (f-MWCNTs)-titanium dioxide (TiO2) composite nanofibers (NFs) with facile electrospinning technique. The synthesized composite NFs were characterized by using X-ray diffraction, field emission scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy techniques. The resistive switching (RS) behavior of the Ag/f-MWCNTs-TiO2/Fluorine-doped tin oxide (FTO) device was studied and memristive properties were calculated. The device shows excellent endurance (~500 cycles) and memory retention (104 s) properties. The electrospun NFs based memory device successfully mimics the spike-timing-dependent plasticity (STDP) based anti-symmetric Hebbian and anti-symmetric anti-Hebbian learning rules. The charge transport mechanism follows the space charge limited current model and RS mechanism was due to the filamentary effect. The results of our investigations asserted that the electrospun f-MWCNTs-TiO2 composite NFs are potential material for memory and synaptic learning applications.

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.

Correlation of Space Charge Limited Current and γ-Ray Response of CdxZn1-xTe1-ySey Room-Temperature Radiation Detectors

In this letter we report a direct correlation between the space charge limited current flow and radiation detection properties of Cd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (CZTS) detector. CZTS is a recently discovered quaternary wide bandgap semiconductor for room-temperature gamma photon detection. The CZTS single crystals have been grown in-house using a modified Bridgman technique. Planar detectors were fabricated and characterized in terms of charge carrier flow and radiation detection measurements. An anomalous current flow falling outside the Lampert's triangle in logJ - logV plot, has been observed which is not generally seen in semiconductor detectors governed by space-charge limited current flow mechanism. The anomalous behavior has been attributed to the presence of electron traps. The devices were tested for their radiation detection properties by acquiring pulse height spectra using <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">241</sup> Am and a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs isotopes as a source of alpha particles and gamma photons, respectively. It was further noticed that the only detectors which worked satisfactorily as radiation detectors, did not exhibit the anomalous current flow mechanism.

Space Charge-Limited Current Transport Mechanism in Crossbar Junction Embedding Molecular Spin Crossovers.

Spin crossover complexes are among the most studied classes of molecular switches and have attracted considerable attention for their potential technological use as active units in multifunctional devices. A fundamental step toward their practical implementation is the integration in macroscopic devices adopting hybrid vertical architectures. First, the physical properties of technological interest shown by these materials in the bulk phase have to be retained once they are deposited on a solid surface. Herein, we describe the study of a hybrid molecular inorganic junction embedding the spin crossover complex [Fe(qnal)2] (qnal = quinoline-naphthaldehyde) as an active switchable thin film sandwiched within energy-optimized metallic electrodes. In these junctions, developed and characterized with the support of state of the art techniques including synchrotron Mössbauer source (SMS) spectroscopy and focused-ion beam scanning transmission electron microscopy, we observed that the spin state conversion of the Fe(II)-based spin crossover film is associated with a transition from a space charge-limited current (SCLC) transport mechanism with shallow traps to a SCLC mechanism characterized by the presence of an exponential distribution of traps concomitant with the spin transition temperature.

Bipolar resistive switching behavior and conduction mechanisms of composite nanostructured TiO2/ZrO2 thin film

In this work, TiO2/ZrO2 bilayer thin film was prepared on fluorine doped tin oxide (FTO)/glass substrates by using a simple and low-cost chemical solution deposition method. Reproducible bipolar resistive switching (RS) characteristics in Au/TiO2/ZrO2/FTO/glass devices are reported in this work. TiO2/ZrO2 bilayer thin films prepared in this work shows reversible bipolar resistive switching and unidirectional conduction performances under applying voltage and these special performances of TiO2/ZrO2 bilayer thin films was first reported. Obvious resistive switching performance can be observed after setting a compliance current, the ratio of high/low resistance reached about 100 at a read voltage of +0.1V and −0.1V and the RS properties showed no obvious degradation after 100 successive cycles tests. The resistive switching characteristics of Au/TiO2/ZrO2/FTO/glass device can be explained by electron trapping/detrapping related with the vacancy oxygen defects in TiO2/ZrO2 bilayer thin film layer. According to slope fitting, the main conduction mechanisms of the sample are Ohmic and Space charge limited current mechanism.

Effect of surface modification on Tb doped bismuth ferrite nanofiller in polyvinyl alcohol based composite films

In this paper, we report the fabrication and the characterizations of surface modified Tb doped bismuth ferrite nanoparticle embedded polyvinyl alcohol (PVA) films. This work begins with the synthesis of Tb doped bismuth ferrite (BTFO) nanoparticles (NPs). BTFO NPs are then functionalized using silanes. Here, the functionalizing agents are tetraethyl orthosilicate (TEOS) and (3-amino propyl) triethoxysilane. Morphological studies confirm that silica coated BTFO NPs possess a distorted hexagonal structure and effectively show less agglomeration. Untreated and functionalized BTFO NPs are embedded in PVA to fabricate flexible polymer nanocomposite systems. After functionalization, BTFO shows uniform dispersion in a PVA matrix. Optical bandgap decreases in functionalized BTFO loaded PVA films due to the increase in charge transfer complexes. BTFO-PVA nanocomposites (treated/untreated) are more thermally stable than the pristine PVA film. The charge carriers of each polymer film follow a correlated barrier hopping conduction mechanism. The outer silica shell thickness of BTFO NPs effectively affects the magnetic property of the films. Enhancement of the magnetic properties is best achieved in the TEOS functionalized BTFO loaded PVA nanocomposite. All the films follow both Ohmic (at lower voltage) and trap controlled space charge limited current (at higher voltage) conduction mechanisms. Considering the effect of intrinsic properties of the polymeric system, the trap controlled current conduction is further well explained by a Poole–Frenkel model. Among the film samples we have examined in this work, TEOS functionalized BTFO–PVA nanocomposite exhibits the best quality in optical, electrical, and magnetic observations.

Dependence of mobility and charge injection on active layer thickness of bulk heterojunction organic solar cells: PCBM:P3HT

The asymmetric behavior in the dark current of any solar cell is essential for decoupling recombination and charge extraction for efficient charge collection. Therefore current density dependence on applied voltage can be used to investigate the complex interplay between bulk charge transport, interface exchange effects and recombination mechanisms. In the present work, we investigate from dark current–density [J(V)] of bulk heterojunction solar cells, the dependence of mobility and charge injection mechanisms on different blend layer thicknesses. The active layer thickness has been established through varying the spin-coating speeds between 1000, 2000, 3000 and 4000 revolutions per minute (rpm) and confirmed by a dektak surface profilometer. The carrier mobility (μ) as a factor limiting the efficiency of organic solar cells was investigated from dark space charge limited current and trap free space charge limited current conduction mechanisms to distinguish between charge extraction and recombination. This approach allows the determination of the effects of threshold field through variation of the active layer thickness (ALT) on the potential barrier height $$(\phi_{B} )$$ at the electrode contacts. Low values of charge carrier mobilities (10–6 cm2 V−1 s−1) in the trap free space charge limited current conduction region have been correlated to the Langevin recombination constants. In the ohmic region, the highest dark carrier mobility corresponded to the 77.1 nm ALT. Further we observe a shift in the transition voltage at the inflection point of J–V curves with increasing film thickness in the forward bias.