Poole-Frenkel Conduction Mechanism Research Articles

Characterization of electrical transport and properties of an Al/porous Si (PS)/p-Si/Al heterojunction

In this paper is discussed the current transport characteristics of an Al/PS/p-Si/Al heterojunction device with a porous silicon layer (PS) fabricated by the electrochemical anodization process and its current transport properties are investigated by the using temperature dependent current-voltage (I-V) measurements in a wide temperature range from 50 K to 300 K. The electrical parameters are characterized with the thermionic emission theory. It is observed that the main characteristics such as ideality factor and apparent barrier height demonstrate resolute temperature dependences and this situation is related to the structure of porous region. In addition, it is obtained the conductance curves for the forward and reverse bias values of Al/PS/p-Si/Al sample and as a result, the value of the relative dielectric constant εr of porous layer is calculated as εr:3.72. From the reverse bias I-V curves, it is discussed the current conduction mechanism of porosity region by using Poole-Frenkel emission and Schottky emission. In result, it is commented that the charge transport in PS is through Poole-Frenkel conduction mechanism for Al/PS/p-Si/Al.

Enhancing Blue Emission in Ce Doped Silicon Oxynitrides Based Electroluminescent Devices

Ce-doped SiOxNy and SiAlON matrices are promising materials for blue LED applications. The uniqueness of this approach stems from the fact that SiOxNy, as a host, combines specific properties of individual SiOx and SiNy matrices like solubility, efficient emission, 5 eV gap, with a broad excitation range from 400 nm to 500 nm of Ce3+ ions due to the 4f-5d transitions. Furthermore, the co-doping with aluminum enhances the Ce3+ emission. In this work, we fabricated electroluminescent devices using SiOxNy:Ce3+ and SiAlON:Ce3+ as active layers and investigated the resulting emission under optical and electrical excitations as a function of nitrogen, cerium and aluminum concentrations. I-V measurements were conducted to determine the SiOxNy:Ce3+ layer electrical parameters. Charge transport through the devices obeys the Poole-Frenkel conduction mechanism. It was demonstrated that by optimizing the SiOxNy:Ce3+ growth parameters, an improvement of electroluminescence yield can be achieved with a maximum intensity obtained for devices with cerium content of 4 at.%.

Effects of Copper Migration on the Reliability of Through-Silicon Via (TSV)

Non-destructive electrical characterization was performed to detect copper migration in a degraded through-silicon via structure after various stressing conditions, such as elevated temperature exposure, temperature cycling, and electrical biasing. They were performed either independently or as a combination with electrical bias for comparison. Variations in the electrical characteristics reflect the presence of copper. The electrical characteristics were also able to monitor the transport of copper ions from an applied electric field. Physical failure analysis was performed to verify the presence of migrated copper, correlating with the changes observed during electrical measurement. With this understanding, reliability assessments become possible where this paper seeks to value add to verify the influence of Cu migration on the conduction mechanism and time-dependent dielectric breakdown (TDDB) lifetime, in which there is currently a lack in understanding. The conduction mechanism was fitted with experimental data before and after degradation and it was deduced that the Poole–Frenkel conduction mechanism is the dominant mechanism after degradation. However, this is dependent on the copper oxidation state which was verified to change over time from Cu2O to CuO by X-ray photoelectron spectroscopy. TDDB experiments were also performed based on this understanding and found that the presence of copper may accelerate or decelerate time to failure. TDDB lifetime was fitted experimentally and is found to be in good agreement with the $\sqrt {E} $ model. It was verified experimentally by measuring the time to failure at low ${E}$ -field within reasonable failure time, rather than extrapolating from data at high field.

Mechanisms of electrical conductivity in CNT/silicone composites designed for neural interfacing

This work presents an investigation of the electrical behavior of composites based on silicone and carbon nanotubes «Taunit». Fabricated films of composites with different concentrations of carbon nanotubes were studied using the method of current-voltage characteristics, and analysis has been made by interpretation of graphs plotted in linearizing coordinates of Schottky, Fowler-Nordheim and Poole-Frenkel mechanisms of conductivity. The applicable conduction mechanism for all samples was found to be Poole-Frenkel conduction mechanism which is favorable for manufacturing of microelectronic devices operating at low voltages, which include neural implants.

Effect of microwave irradiation power on resistive switching performance in solution-processed aluminum oxide resistive memory

In this study, we fabricated ReRAM devices with the structure Ti/AlOx/Pt by applying solution-processed AlOx film as the switching layer. This enabled us to analyze the effect of the MWI power on the resistive switching performance of ReRAM. The AlOx resistive switching layer deposited by the solution-process was subjected to PDA treatment with microwave power ranging from 600 W to 3000 W, and the resistive switching performance was compared with as-dep and CTA-processed ReRAMs. All AlOx-based ReRAM devices exhibited bipolar resistive switching characteristics, and MWI-treated devices had larger memory windows than as-dep and CTA-treated devices. These solution-processed AlOx ReRAMs were found to exhibit Ohmic conduction in the low-voltage range of both the LRS and HRS. The high-voltage range of HRS shows the Poole-Frenkel conduction mechanism. In addition, compared with the as-dep device, the PDA-treated devices exhibited stable endurance characteristics and uniform resistance distribution in 1000 cycles of the switching operation, and showed reliable retention characteristics for 10,000 s at both room temperature and high temperature. XPS measurements were performed to analyze the relationship between the resistive switching performance and chemical nature of the AlOx switching layer by varying the microwave power and heat treatment method.

(Invited) Enhancing the Blue Emission in Ce Doped Silicon Oxynitrides Thin Films for Electroluminescence Device Applications

Ce-doped SiOxNy and SiAlON matrices are promising materials for blue LED applications. The uniqueness of this approach stems from the fact that SiOxNy, as a host, combines specific properties of individual SiOx and SiNy matrices like solubility, efficient emission, 5 eV gap etc. with a broad excitation range (400 to 500 nm) of Ce3+ due to the 4f-5d transitions. Furthermore, the co-doping with aluminum enhances the Ce3+ emission. In this work, we fabricated electroluminescent devices using SiOxNy: Ce3+ and SiAlON: Ce3+ as an active layers and studied the resulting emission under optical and electrical excitation as a function of nitrogen, cerium and aluminum concentrations. I-V measurements were conducted to determine the SiOxNy: Ce3+ layer electrical parameters. The transport through the devices obeys a Poole-Frenkel conduction mechanism. It was demonstrated that by optimizing the SiOxNy:Ce3+ material growth parameters an improvement of electroluminescence yield can be achieved with maximum intensity achieved for devices with Ce content of 4 at.%.

Near-infrared electroluminescence from atomic layer doped Al2O3:Yb nanolaminate films on silicon

Nanolaminate Al2O3:Yb films are fabricated by atomic layer deposition on silicon, from which intense 977nm electroluminescence is obtained. By precise controlling the Yb agglomerate and the distance among Yb3+ ions, the power density up to 2.67mWcm−2 and external quantum efficiency of 1.8% are estimated from the nominal 1.27 at.% doped device. The charge transport is ascribed to the Poole-Frenkel conduction mechanism and the electroluminescence originates from the impact-excitation of Yb3+ ions by hot electrons. The distance for the presence of non-radiative interaction of Yb3+ ions in Al2O3 matrix is concluded to be ~3nm.

Investigation of the in-plane and out-of-plane electrical properties of metallic nanoparticles in dielectric matrix thin films elaborated by atomic layer deposition

Pt nanoparticles in a Al2O3 dielectric matrix thin films are elaborated by means of atomic layer deposition. These nanostructured thin films are integrated in vertical and planar test structures in order to assess both their in-plane and out-of-plane electrical properties. A shadow edge evaporation process is used to develop planar devices with electrode separation distances in the range of 30 nm. Both vertical and planar test structures show a Poole–Frenkel conduction mechanism. Low trap energy levels (<0.1 eV) are identified for the two test structures which indicates that the Pt islands themselves are not acting as traps in the PF mechanism. Furthermore, a more than three order of magnitude current density difference is observed between the two geometries. This electrical anisotropy is attributed to a large electron mobility difference in the in-plane and out-of-plane directions which can be related to different trap distributions in both directions.

Electrical Conduction and mechanical properties of irradiated clay nanoparticles /SBR rubber composites

Styrene butadiene Rubber (SBR) containing Surface Modified Nano particles Clay by Electron Beam Radiation dose 100 KGy (SMEB) and non-modified Nano particles Clay were prepared. Direct current measurements were established for knowing the conduction type of charge transport passing through the modified (SMEB) and unmodified SBR/clay composite samples. Where, it is deduced that Poole-Frenkel conduction mechanism was found to be predominate for all clay-SBR samples. The mechanical Tensile strength and elongation at break were estimated from stress strain curves measured and we realize the tensile strength of SBR matrix increases appreciably with clay loading up to 15 phr, the polymer-filler interaction for modified clay loaded samples is improved slightly higher than unmodified clay samples and From calculations of the slope of the Vro/Vrf versus C/ (1-C) plot. The slop value is founded to be positive which mean that reinforcing by filler having good polymer-filler interaction. Elongation at break increases slightly with clay loading up to 10 phr and then abrupt decrease is detected at 15 phr clay loading for all samples.

Te-based chalcogenide materials for selector applications

The implementation of dense, one-selector one-resistor (1S1R), resistive switching memory arrays, can be achieved with an appropriate selector for correct information storage and retrieval. Ovonic threshold switches (OTS) based on chalcogenide materials are a strong candidate, but their low thermal stability is one of the key factors that prevents rapid adoption by emerging resistive switching memory technologies. A previously developed map for phase change materials is expanded and improved for OTS materials. Selected materials from different areas of the map, belonging to binary Ge-Te and Si-Te systems, are explored. Several routes, including Si doping and reduction of Te amount, are used to increase the crystallization temperature. Selector devices, with areas as small as 55 × 55 nm2, were electrically assessed. Sub-threshold conduction models, based on Poole-Frenkel conduction mechanism, are applied to fresh samples in order to extract as-processed material parameters, such as trap height and density of defects, tailoring of which could be an important element for designing a suitable OTS material. Finally, a glass transition temperature estimation model is applied to Te-based materials in order to predict materials that might have the required thermal stability. A lower average number of p-electrons is correlated with a good thermal stability.

ZnO and ZnO1−x based thin film memristors: The effects of oxygen deficiency and thickness in resistive switching behavior

In this study, direct-current reactive sputtered ZnO and ZnO1-x based thin film (30 nm and 300 nm in thickness) memristor devices were produced and the effects of oxygen vacancies and thickness on the memristive characteristics were investigated. The oxygen deficiency of the ZnO1-x structure was confirmed by SIMS analyses. The memristive characteristics of both the ZnO and ZnO1-x devices were determined by time dependent current-voltage (I-V-t) measurements. The distinctive pinched hysteresis I-V loops of memristors were observed in all the fabricated devices. The typical homogeneous interface and filamentary types of memristive behaviors were compared. In addition, conduction mechanisms, on/off ratios and the compliance current were analyzed. The 30 nm ZnO based devices with native oxygen vacancies showed the best on/off ratio. All of the devices exhibited dominant Schottky emissions and weaker Poole-Frenkel conduction mechanisms. Results suggested that the oxygen deficiency was responsible for the Schottky emission mechanism. Moreover, the compliance currents of the devices were related to the decreasing power consumption as the oxygen vacancies increased.

In situ TEM observation on the interface-type resistive switching by electrochemical redox reactions at a TiN/PCMO interface.

The interface-type resistive switching devices exhibiting bipolar and multi-level resistive switching have been considered as the key component for neuromorphic device applications. To directly observe the microscopic details of underlying electrochemical redox reactions occuring at a metal/oxide interface, we implemented in situ resistive switching of TiN/Pr0.7Ca0.3MnO3 (PCMO)/Pt junction devices in a transmission electron microscope (TEM). The in situ TEM observations directly show that an intermediate reaction layer (TiOxNy), growing and shrinking in the thickness range of a few nanometers at the TiN/PCMO interface in response to the applied voltage, mainly determines the device resistance by limiting the transport of charge carriers via the Poole-Frenkel conduction mechanism. A detailed analysis of in situ TEM observations demonstrates that electrochemical redox reactions at the TiN/PCMO interface are facilitated by the electric field driven drift of oxygen as well as Ti ions with a much stronger influence of the oxygen ions. As such, the reaction kinetics are governed by the electric field acting across the TiOxNy reaction layer. This layer defines the critical field for the onset of switching, which is measured to be of the order of 106 V cm-1, a typical value at which the ionic drift velocity starts increasing exponentially with the field according to the nonlinear ionic drift model. The present results indicate that understanding the nature of the electric field driven drift of ions in a nanoscale solid electrolyte is a key to the precise control of the resistive switching of metal/insulator/metal junction devices via voltage stimulations.

Effects of electrode on resistance switching properties of ZnMn2O4 films deposited by magnetron sputtering

ZnMn2O4 films for resistance random access memory (RRAM) were fabricated with different device structures by magnetron sputtering. The effects of electrode on I-V characteristics, resistance switching behavior, endurance and retention characteristics of ZnMn2O4 films were investigated. The ZnMn2O4 films, using p-Si and Pt as bottom electrode, exhibit bipolar resistive switching (BRS) behavior dominated by the space-charge-limited conduction (SCLC) mechanism in the high resistance state (HRS) and the filament conduction mechanism in the low resistance state (LRS), but the ZnMn2O4 films using n-Si as bottom electrodes exhibit both bipolar and unipolar resistive switching behaviors controlled by the Poole-Frenkel (P-F) conduction mechanism in both HRS and LRS. Ag/ZnMn2O4/p-Si device possesses the best endurance and retention characteristics, in which the number of stable repetition switching cycle is over 1000 and the retention time is longer than 106 seconds. However, the highest RHRS/RLRS ratio of 104 and the lowest VON and VOFF of 3.0 V have been observed in Ag/ZnMn2O4/Pt device. Though the Ag/ZnMn2O4/n-Si device also possesses the highest RHRS/RLRS ratio of 104, but the highest values of VON,VOFF, RHRS and RLRS, as well as the poor endurance and retention characteristics.

Leakage Current Paths in Isolated AlGaN/GaN Heterostructures

Electrical characterization of AlGaN/GaN heterojunctions isolated by Ar-implantation identified three conduction regimes. These include an Ohmic regime below 100 V associated with conduction across the implanted area itself as well as an exponential regime above 400 V associated with a conduction across the buffer or buried interfaces with the substrate. While the extraction of activation energies found an average of roughly 0.85 eV for the Ohmic regime, activation energies above 400 V were consistent with a Poole-Frenkel conduction mechanism. Variations in epitaxial structure, lateral and vertical electric field enabled the distinction between a conduction path in the top layers of the structure and a conduction path which is at least partially vertical across the structure. In addition, time-dependent measurements showed a capacitive effect for conduction across the buffer at room temperature. Having identified the performance limiting conduction path through the buffer layers, these experimental results can also be used as a tool for epitaxy assessment very early on in the production process.

Electrical characterisation of epitaxial AlN/Nb 2 N heterostructures grown by molecular beam epitaxy

Initial electrical characterisation of epitaxial AlN/Nb2N heterostructures grown by molecular beam epitaxy on 6H-SiC substrates is presented. Metal–insulator–metal (MIM) devices of varying diameter were used for current–voltage and capacitance–voltage (C–V) measurements at various temperatures. From C–V measurements, a dielectric constant of 10.1 was extracted along with a linear dependence of capacitance on temperature of 0.02 nF/cm2/°C. Leakage current was determined to be consistent with a Poole–Frenkel conduction mechanism at electric fields >1.25 MV/cm with an extracted trap ionisation energy of 0.82 eV. Electric field breakdown ranged between 3.4 and 5.6 MV/cm with some dependence on the diameter of the MIM device. These initial findings demonstrate the potential for high-power devices based on AlN.

Electrical conduction mechanism in GeSeSb chalcogenide glasses

Electrical conductivity of chalcogenide glassy system Ge30−xSe70Sbx (x = 10, 15, 20 and 25) prepared by melt quenching has been determined at different temperatures in bulk through the I–V characteristic curves. It is quite evident from results that Poole–Frenkel conduction mechanisms hold good for conduction in these glasses in a given temperature range. The variation in electrical conductivity with composition was attributed to the Se–Sb bond concentration in the Se–Ge–Sb system. Results indicated that Ge5Se70Sb25 showed the minimum resistance. In view of this the composition Ge5Se70Sb25 may be coined as ‘critical composition’ in the proposed series. Also the activation energies of conduction of these glassy alloys have been calculated in higher and lower temperature range using the Arrhenius equation.

Bond Formation Perspective: Effect of Sn Addition in Se-Te-Sn Chalcogenide Glasses

The aim of this study is to investigate the effect of Tin (Sn) addition on Band gap (Eg) and Dc conductivity of Se-Te-Sn semi-conducting glasses. This is an effort towards the understanding of physics of temperature dependence of dc electrical volume conductivity of Se75Te25-xSnx (X= 2, 4, 6 & 8) glasses in bulk form. These Chalcogenide glasses were prepared by melt quenching (rapid cooling of melt) technique. The amorphous nature of as prepared glass was confirmed by XRD. Using Keithley Electrometer / High resistance Meter 6517 A, the I-V characteristics of these glasses have been recorded in a temperature range from room temperature to 100˚C. Additionally, the Poole-Frenkel conduction mechanism has also been verified in order to investigate the good agreement with the established fact that most of Chalcogenide glasses obey Poole-Frenkel conduction mechanism. To calculate the Band gap, with the help of Ocean Optics Spectrophotometer, absorption spectra has been recorded. Analysis of these absorption spectra using Tauc relation reveals that these glasses are semiconducting and direct band gap material.

TCAD analysis of the leakage current and breakdown versus temperature of GaN-on-Silicon vertical structures

A TCAD-based approach has been used to investigate the leakage current and breakdown regime of vertical GaN/AlGaN/Si structures at different ambient temperatures. TCAD modeling has been used to assess possible mechanisms of the forward-bias leakage current. A good agreement with experimental data has been obtained by implementing both trap-assisted and Poole–Frenkel conduction mechanisms into the deeper buffer layers, indicating that conduction is dominated by electron injection from silicon into a continuum of states at a given energy offset in the transition layer, which might be associated with conductive dislocation defects. The latter mechanisms have been proven to anticipate the onset of breakdown at high temperatures.

Enhancement of the saturation mobility in a ferroelectric-gated field-effect transistor by the surface planarization of ferroelectric film

Ferroelectricity refers to the property of a dielectric material to undergo spontaneous polarization which originates from the crystalline phase. Hence, ferroelectric materials have a certain degree of surface roughness when they are formed as a thin film. A high degree of surface roughness may cause unintended phenomena when the ferroelectric material is used in electronic devices. Specifically, the quality of subsequently deposited film could be affected by the rough surface. The present study reports that the surface roughness of ferroelectric polymer film can be reduced by a double-spin-coating method of a solution, with control of the solubility of the solution. At an identical thickness of 350nm, double-spin-coated ferroelectric film has a root-mean-square roughness of only 3nm, while for single-spin-coated ferroelectric film this value is approximately 16nm. A ferroelectric-gated field-effect transistor was fabricated using the proposed double-spin-coating method, showing a maximum saturation mobility as much as seven-fold than that of a transistor fabricated with single-spin-coated ferroelectric film. The enhanced saturation mobility could be explained by the Poole–Frenkel conduction mechanism. The proposed method to reduce the surface roughness of ferroelectric film would be useful for high performance organic electronic devices, including crystalline-phase dielectric film.

Electrical conduction mechanisms of CdTe quantum dots/p-si heterojunction

CdTe quantum dots (QDs) are prepared on p-Si substrates using thermal evaporation technique. Current–voltage (I–V) characteristics of Au/CdTe QDs/p-Si/Al heterojunction are measured in a temperature range 304–368K. The results show that the device has a rectification behavior with a rectification ratio being 275 at ±1.5V. We determine the electrical conduction mechanisms of the heterojunction. At forward voltages V<0.3V, the thermionic emission becomes the main mechanism, where in this voltage range, it is possible to estimate the barrier height and the ideality factor. At a forward voltage range 0.5<V<0.9V, the conduction mechanism turns into the space charge limited conduction which is dominated by an exponential trap distribution (TSCLC). Within this voltage range 0.5<V <0.9, the total density of the trap states is calculated. At forward voltages 0.95<V<1.5V, Poole-Frenkel conduction mechanism fits well with the experimental data. It is found that there are two trap levels with zero fields of the activation energy which have values 0.16 and 0.46eV. At the reverse applied voltages, it is also found that the main source of the reverse current is the generation-recombination through p-Si rather than through the interface of the thin film itself.