Temperature-dependent Current-voltage Research Articles

Role of doping level, electric field and temperature on the charge transport properties of electrochemically polymerized poly(3-butylthiophene) and poly(3-hexylthiophene) devices

Abstract In this article, the charge transport properties of electrochemically polymerized poly(3-butylthiophene) (P3BT) and poly(3-hexylthiophene) (P3HT) devices using a sandwiched metal/polymer/metal structure are explored. These devices are successfully fabricated at different doping levels using electrochemical polymerization and thermal evaporation techniques. Low temperature-dependent Current-Voltage (I-V) measurement reveals that space charge limited conduction (SCLC) mechanism with a field and temperature-dependent mobility in the form of the Poole-Frenkel model governs the transport mechanism. The zero-field dependent mobility exhibits a thermally activated behavior, with two activation processes observed- one at higher and another at lower temperatures. The activation energy increases with the decrease in doping level at higher temperature regions, indicating the significant role of doping level in the activation process. However, electric field plays a significant role in the transport mechanism at lower temperatures. Comparatively, P3HT devices exhibit lower conductivity and mobility values than P3BT devices. The mobility ratio μ(0,300K)/μ(0,50K) for P3HT devices is considerably larger than that for P3BT devices. Additionally, the activation energy of P3HT devices is higher, providing evidence of a higher relative energetic disorder than P3BT devices.

Current-driven mechanical motion of double stranded DNA results in structural instabilities and chiral-induced-spin-selectivity of electron transport.

Chiral-induced-spin-selectivity of electron transport and its interplay with DNA's mechanical motion are explored in a double stranded DNA helix with spin-orbit-coupling. The mechanical degree of freedom is treated as a stochastic classical variable experiencing fluctuations and dissipation induced by the environment as well as force exerted by nonequilibrium, current-carrying electrons. Electronic degrees of freedom are described quantum mechanically using nonequilibrium Green's functions. Nonequilibrium Green's functions are computed along the trajectory for the classical variable taking into account dynamical, velocity dependent corrections. This mixed quantum-classical approach enables calculations of time-dependent spin-resolved currents. We showed that the electronic force may significantly modify the classical potential, which, at sufficient voltage, creates a bistable potential with a considerable effect on electronic transport. The DNA's mechanical motion has a profound effect on spin transport; it results in chiral-induced spin selectivity, increasing spin polarization of the current by 9% and also resulting in temperature-dependent current voltage characteristics. We demonstrate that the current noise measurement provides an accessible experimental means to monitor the emergence of mechanical instability in DNA motion. The spin resolved current noise also provides important dynamical information about the interplay between vibrational and spin degrees of freedom in DNA.

Temperature- and gate voltage-dependent I–V modeling of GaN HEMTs based on ASM-HEMT

Abstract In this paper, a temperature and gate voltage dependent current-voltage (I-V) model for Gallium nitride (GaN) high electron mobility transistors (HEMTs) devices is studied. In order to help researchers and designers simulate devices in the absence of experimental data and improve parameter extraction efficiency, the temperature and gate voltage dependence of mobility are discussed and incorporated into the proposed model which is revised from the standard advanced SPICE model (ASM) for GaN HEMTs. The mobility variations with gate voltage from -2 V to 6 V and temperature from 10 K to 1000 K are analyzed. The simulation results of our model are compared with the standard ASM-HEMT model, and the output and transfer characteristics of the device from 270 K to 420 K are simulated. Thereby, our model may simulate various applications of GaN HEMTs at different gate voltages and temperatures in the early stages of design and research.

Phonon-assisted leakage current of InGaN light emitting diode

We report on the leakage current mechanism in a blue GaN-based light-emitting diode (LED). The device structure was grown by the MOCVD technique on a sapphire substrate. The LED was characterized through various measurements including current-voltage, electroluminescence, and secondary ion mass spectroscopy (SIMS). Capacitance-voltage measurements were employed to calculate the depletion layer thickness at different bias voltages and to analyze the doping profile in the active layer. The reverse temperature-dependent current-voltage measurements were carried out to study the leakage mechanism. The leakage current was explained by phonon-assisted tunneling of charge carriers through deep trap states. The trap energy and density of states were extracted from the application of the introduced model. Cathodoluminescence measurements were performed to evaluate the density of dislocations, which were then compared to x-ray diffraction measurements. The determined value was close to the density of states obtained from the tunneling model.

Substitution of an isovalent Te-ion in SnSe thin films for tuning optoelectrical properties

Substitution of an isovalent Te-ion in SnSe thin films for tuning optoelectrical properties

Adjustment in phonon scattering through doping to boosting the Near-IR photoresponse performance of p-type SnSe nanosheets

Adjustment in phonon scattering through doping to boosting the Near-IR photoresponse performance of p-type SnSe nanosheets

Small polaron hopping and tunneling transport in Maxwell–Wagner relaxation dominated Al2O3/TiO2 subnanometric laminates

Maxwell–Wagner relaxation dominated Al2O3/TiO2 nanolaminates (ATA NLs) have recently demonstrated their potential for high-density energy storage applications. In this report, we have unraveled the defect-mediated transport mechanisms prevailing in Al2O3/TiO2 sub-nanometric laminates. Temperature-dependent ac conductivity measurements revealed the signature of small polaron hopping in TiO2 active layers and trap-assisted tunneling transport through Al2O3 barrier layers, which was corroborated by resonant photoelectron spectroscopy and temperature-dependent current–voltage measurement. The polaronic defect states, found ∼1 eV below the Fermi level, served as the hopping centers and leakage paths for current. The signature of quantum tunneling transport and the negative differential conductance observed toward higher electric field was attributed to the splitting of delocalized minibands. These transport properties of Al2O3/TiO2 nanolaminates will help in tailoring these materials for next-generation storage capacitors.

Multi-Gaussian distribution of barrier height in diamond-like carbon interfacial-layered Schottky devices

Multi-Gaussian distribution of barrier height in diamond-like carbon interfacial-layered Schottky devices

Analysis of temperature-dependent current–voltage characteristics of Schottky diodes by the modified thermionic emission current model

We have investigated the behavior of current flow across an inhomogeneous Schottky diode (SD) as a function of temperature by numerical simulation. We have used the modified thermionic emission (TE) current expression with a Gaussian distribution of potential barrier heights. This modified TE model assumes the presence of a series of low-barrier patches at the Schottky contact and semiconductor interface. First, we have discussed the behavior of the patch current compound relative to the TE compound in the inhomogeneous SD at 300, 200, and 100 K, as a function of standard deviation and the number of circular patches N. Then, we have investigated the behavior of temperature- and bias-dependent and bias-independent current vs voltage (I–V–T) characteristics in the 75–300 K range. In bias-dependent I–V–T curves obtained for σ1=4.35×10−5cm2/3V1/3 and σ2=7.35×10−5cm2/3V1/3 at N1=1.81×106 or N2=1.81×108, an intersection behavior has been observed in the I–V curve at 75 K for σ2 at both N values; however, the same behavior has been not observed for σ1 at both N values due to σ1<σ2. That is, the current for σ2 at 75 K has exceeded the current at higher temperatures. This behavior has been ascribed to the effective BH to decrease with decreasing temperature value. In the I–V–T curves independent of bias, such an intersection has not been observed for σ1 while it has been observed for σ2 in the I–V curves at both 75 and 100 K. Thus, it has been concluded that the bias-dependeσnt I–V equations must be used to avoid this intersection behavior while fitting the experimental I–V curve of an SD to the theoretical I–V curve.

Current transport mechanism of lateral Schottky barrier diodes on β-Ga2O3/SiC structure with atomic level interface

Heterogeneous integration of β-Ga2O3 on highly thermal conductive SiC substrate by the ion-cutting technique is an effective solution to break the heat-dissipation bottleneck of β-Ga2O3 power electronics. In order to acquire high-quality β-Ga2O3 materials on SiC substrates, it is essential to understand the influence of the ion-cutting process on the current transport in β-Ga2O3 devices and to further optimize the electrical characteristics of the exfoliated β-Ga2O3 materials. In this work, the high quality of β-Ga2O3/SiC structure was constructed by the ion-cutting process, in which an amorphous layer of only 1.2 nm was formed between β-Ga2O3 and SiC. The current transport characteristics of Au/Pt/Ni/β-Ga2O3 Schottky barrier diodes (SBDs) on SiC were systematically investigated. β-Ga2O3 SBDs with a high rectification ratio of 108 were realized on a heterogeneous β-Ga2O3 on-SiC (GaOSiC) substrate. The net carrier concentration of the β-Ga2O3 thin film for GaOSiC substrate was down to about 8% leading to a significantly higher resistivity, compared to the β-Ga2O3 donor wafer, which is attributed to the increase in acceptor-type implantation defects during the ion-cutting process. Furthermore, temperature-dependent current–voltage characteristics suggested that the reverse leakage current was limited by the thermionic emission at a low electric field, while at a high electric field, it was dominated by the Poole–Frenkel emission from E3 deep donors caused by the implantation-induced GaO antisite defects. These results would advance the development of β-Ga2O3 power devices on high thermal conductivity substrate fabricated by ion-cutting technique.

Magnetoresistance properties in nickel-catalyzed, air-stable, uniform, and transfer-free graphene

A transfer-free graphene with high magnetoresistance (MR) and air stability has been synthesized using nickel-catalyzed atmospheric pressure chemical vapor deposition. The Raman spectrum and Raman mapping reveal the monolayer structure of the transfer-free graphene, which has low defect density, high uniformity, and high coverage (>90%). The temperature-dependent (from 5 to 300 K) current–voltage (I–V) and resistance measurements are performed, showing the semiconductor properties of the transfer-free graphene. Moreover, the MR of the transfer-free graphene has been measured over a wide temperature range (5–300 K) under a magnetic field of 0 to 1 T. As a result of the Lorentz force dominating above 30 K, the transfer-free graphene exhibits positive MR values, reaching ∼8.7% at 300 K under a magnetic field (1 Tesla). On the other hand, MR values are negative below 30 K due to the predominance of the weak localization effect. Furthermore, the temperature-dependent MR values of transfer-free graphene are almost identical with and without a vacuum annealing process, indicating that there are low density of defects and impurities after graphene fabrication processes so as to apply in air-stable sensor applications. This study opens avenues to develop 2D nanomaterial-based sensors for commercial applications in future devices.

Temperature dependent electron transport and interface state studies on Ni/n-Si/Al/Ag lateral Schottky junction

Temperature dependent electron transport and interface state studies on Ni/n-Si/Al/Ag lateral Schottky junction

Radiation effects of high-fluence reactor neutron on Ni/ β -Ga2O3 Schottky barrier diodes

This study investigates the broad-energy-spectrum reactor-neutron irradiation effects on the electrical characteristics of Ni/β-Ga2O3 Schottky barrier diodes (SBDs), where the irradiated neutron fluence was up to 1 × 1016 cm−2. On the one hand, the high neutron fluence of 1016 cm−2 resulted in a reduction in forward current density by two orders of magnitude and an extremely high on-resistance property due to the radiation-generated considerable series resistance in the SBD. On the other hand, the irradiation brought little influence on the Ni/β-Ga2O3 Schottky contact, since the extracted ideality factor and barrier height from temperature-dependent current–voltage (I–V–T) characteristics showed no significant changes after the radiation. Moreover, the capacitance–voltage (C–V) characterization revealed that the net carrier density in the β-Ga2O3 material was only reduced by 25% at the neutron fluence of 1015 cm−2 but a significant reduction by 2–3 orders at 1016 cm−2. Within the neutron fluence range of 2 × 1014 cm−2 up to 1016 cm−2, the carrier removal rates trended to be saturated with the increased fluences, following an exponential regular. In addition, the C–V measurement on the 1016 cm−2 irradiated sample exhibited an obvious frequency dispersion, and the extracted carrier distribution was not uniform.

Modeling and calibration of electrical features of p-n junctions based on Si and GaAs

This study provides a detailed analysis of the temperature-dependent electrophysical properties and current-voltage (I-V) characteristics of p-n junction structures based on Silicon (Si) and Gallium Arsenide (GaAs). The investigation spans a temperature range of 0–1000 K, examining key parameters such as bandgap, mobility, intrinsic carrier concentration, and I-V characteristics. Advanced modeling and calibration techniques were employed to reveal intricate thermal dependencies of these parameters and their impact on device behavior. The results demonstrate that recombination currents dominate at low forward biases (0.1–0.3 V), characterized by an ideality factor near 2, while diffusion currents prevail between 0.3–0.7 V, with an ideality factor approaching 1. At higher voltages, high-injection conditions emerge. In Si, diffusion mechanisms dominate from 0.4–0.7 V, while in GaAs, recombination remains the primary mechanism up to 1.2 V. These findings are corroborated by semi-logarithmic I-V curves, illustrating the distinct transitions between current mechanisms. This comprehensive study highlights the robustness of the proposed models in accurately capturing the temperature-dependent behavior of these materials. The insights gained offer valuable implications for optimizing p-n junction-based devices across a wide temperature range. Future research will extend these models to explore more advanced semiconductor structures and operational scenarios.

Understanding Performance Limitations in Water Splitting Photoelectrodes at the Nanoscale

Photoelectrochemical (PEC) water splitting is a promising route for efficient conversion of solar energy into chemical fuels. In this context, economically viable photosystems are often based of semiconductor thin films which are polycrystalline or nanostructured with highly complex architectures e.g. with boundaries between differently orientated grains, different crystal facet orientations, as well as locally varying composition or phase. These nano- to micrometer properties often control critical processes, such as efficiency and stability, of the macroscale system. To understand the impact of nanoscale properties on the macroscopic performance, we aim at resolving local structural, chemical, and optoelectronic heterogeneities and at elucidating their effect on light-driven processes.In this work, we use a correlative approach to elucidate the nanoscale properties of polycrystalline BiVO4 thin films – a promising material for solar water splitting. Mapping of the local charge transport properties by photoconductive atomic force microscopy (pc-AFM) reveals the tolerance to grain boundaries.[1] Interestingly, scanning nearfield infrared microscopy shows strongly varying absorption from VO4 stretching modes between grains and at grain boundaries which correlate with the heterogeneities in the local photoconductivity across the polycrystalline thin films. Furthermore, local temperature-dependent current-voltage spectroscopy show that the low intrinsic bulk conductivity of BiVO4 limits the electron transport through the film, and that the transport mechanism can be attributed to space charge limited current (SCLC) in the presence of trap states.[1] Performing the same measurements in-situ in controlled gas-phase environment reveals the influence of chemical interactions of adsorbed oxygen and water on charge transport and interfacial charge transfer.[2] For BiVO4, we demonstrate that adsorbed oxygen acts as a surface trap state for electrons, which enhances the built-in potential and depletes the BiVO4 layer. Overall, combining insights from different nanoscale techniques generates a comprehensive picture of charge separation, transport, and transfer at the nanoscale. The gained nanoscale understanding of energy materials enables the rational design of durable and efficient solar fuel devices.[1] Eichhorn et al., Nat. Commun. 9, 2597(2018).[2] Eichhorn et al., ACS Appl. Mater. Interfaces, 10, 41, 35129 (2018).

Ga-polar GaN Camel diode enabled by a low-cost Mg-diffusion process

In this letter, we show that low-cost physical vapor deposition of Mg followed by a thermal diffusion annealing process increases the effective barrier height at the metal/Ga-polar GaN Schottky interface. Thus, for the first time, GaN Camel diodes with improved barrier height and turn-on voltage were realized compared to regular GaN Schottky barrier diodes. Temperature-dependent current–voltage characteristics indicated a near-homogeneous and near-ideal behavior of the GaN Camel diode. The analysis performed in this work is thought to be promising for improving the performance of future GaN-based unipolar diodes.

Effect of gamma irradiation on β -Ga2O3 vertical Schottky barrier diode

In this paper, the radiation effect of gamma irradiation (60Co) on the Au/Ni/β-Ga2O3 vertical Schottky barrier diodes (SBDs) was investigated for total doses of about 1 Mrad (Si). The SBDs were characterized by current density–voltage (J–V) and capacitance–voltage (C–V) measurements. Compared with original β-Ga2O3 SBDs, it was found that Schottky barrier height Φb increases from 1.08 to 1.12 eV, the ideality factor n decreases from 1.07 to 1.02, and the specific on-resistance Ron,sp decreases from 3.34 to 2.95 mΩ·cm2 for the irradiated β-Ga2O3 SBDs. In addition, the carrier concentration calculated from the C–V measurements increases slightly after gamma irradiation. The temperature-dependent current–voltage characteristics and conductance-frequency measurements indicate that the Schottky contact interface of β-Ga2O3 SBDs had been slightly improved after irradiation. These results suggest that β-Ga2O3 SBDs have high intrinsic gamma irradiation hardness.

Ferroelectric Resistance Switching in Epitaxial BiFeO3/La0.7Sr0.3MnO3 Heterostructures.

BiFeO3/La0.7Sr0.3MnO3 (BFO/LSMO) epitaxial heterostructures were successfully synthesized by pulsed laser deposition on (001)-oriented SrTiO3 single-crystal substrates with Au top electrodes. Stable bipolar resistive switching characteristics regulated by ferroelectric polarization reversal was observed in the Au/BFO/LSMO heterostructures. The conduction mechanism was revealed to follow the Schottky emission model, and the Schottky barriers in high-resistance and low-resistance states were estimated based on temperature-dependent current-voltage curves. Further, the observed memristive behavior was interpreted via the modulation effect on the depletion region width and the Schottky barrier height caused by ferroelectric polarization reversal, combining with the oxygen vacancies migration near the BFO/LSMO interface.

Microelectronics-compatible reduced graphene oxide based nanomechanical resonators capable of all-electrical actuation and read-out

Microelectronics-compatible reduced graphene oxide based nanomechanical resonators capable of all-electrical actuation and read-out

Electrical characteristics of in situ Mg-doped β-Ga2O3 current-blocking layer for vertical devices

The lack of p-type doping has impeded the development of vertical gallium oxide (Ga2O3) devices. Current blocking layers (CBLs) using implanted deep acceptors have been used to demonstrate vertical devices. This paper presents a pioneering demonstration of in situ Mg-doped β-Ga2O3 CBLs grown using metal–organic chemical vapor deposition. The Mg-doping density during growth was calibrated by quantitative secondary ion mass spectroscopy. Electrical test structures were designed with in situ Mg doped layers with various targeted Mg doping concentrations. The effectiveness of the CBL is characterized by using temperature-dependent current–voltage measurements using n-Mg-doped-n structures, providing crucial insight into the underlying mechanisms. Pulsed measurements show similar blocking characteristics as DC. To further validate the experimental results, a TCAD simulation is performed, and the electrically active effective doping is found to be dependent on the Mg-doping density, offering an alternate perspective on the optimization of CBL performance. Breakdown measurements show a peak 4 MV/cm field strength.