Schottky Barrier Research Articles

Low turn-on voltage and 2.3 kV β -Ga2O3 heterojunction barrier Schottky diodes with Mo anode

In this work, we propose combining a low work function anode metal and junction barrier Schottky structure to simultaneously achieve low turn-on voltage (Von) and high breakdown voltage (BV), which alleviates the dilemma that high BV requires high Schottky barrier height (SBH) and high Von. Molybdenum (Mo) is used to serve as the anode metal to reduce the SBH and facilitate fast turn-on to achieve a low Von. To resolve the low SBH related low BV issue, a p-NiO/n-Ga2O3-based heterojunction structure is used to enhance β-Ga2O3 sidewall depletion during the reverse state to improve the BV. With such a design, a low Von = 0.64 V(@1A/cm2) and a high BV = 2.34 kV as well as a specific on-resistance (Ron,sp) of 5.3 mΩ cm2 are demonstrated on a 10 μm-drift layer with a doping concentration of 1.5 × 1016 cm−3. β-Ga2O3 JBS diodes with low Von = 0.64 V and a power figure of merit of 1.03 GW/cm2 show great potential for future high-voltage and high-efficiency power electronics.

Nonvolatile resistive switching in interface-dominated memristors utilizing two-dimensional Cs2Pb(SCN)2Br2 perovskite films

In this study, all-inorganic two-dimensional (2D) perovskite Cs2Pb(SCN)2Br2 was employed in a thin-film vertical structure prototype memristor. The device consisted of a Cs2Pb(SCN)2Br2 film prepared through solution approach, sandwiched between an Ag electrode and a TiO2/FTO substrate bottom electrode. Two types of resistive switching (RS) behaviors were observed within a single device at different temperatures. At room temperature, the dominant control mechanism was the interface Schottky barrier, whereas at higher temperatures, the primary driving force shifted to the conductive channel. The device has an on/off ratio exceeding 103 under the interface control mechanism. The migration of mobile bromine vacancies within the Cs2Pb(SCN)2Br2 film, whose concentration was enhanced by the infiltration and reaction of the Ag active electrode within the Cs2Pb(SCN)2Br2 film, is proposed to be the root cause for both types of RS characteristics. These findings offer insights into the potential application of 2D Cs2Pb(SCN)2Br2 perovskite in RS memory devices.

An Atomically Resolved Schottky Barrier Height Approach for Bridging the Gap between Theory and Experiment at Metal-Semiconductor Heterojunctions.

We propose an atomically resolved approach to capture the spatial variations of the Schottky barrier height (SBH) at metal-semiconductor heterojunctions. This proposed scheme, based on atom-specific partial density of states (PDOS) calculations, further enables calculation of the effective SBH that aligns with conductance measurements. We apply this approach to study the variations of SBH at MoS2@Au heterojunctions, in which MoS2 contains conducting and semiconducting grain boundaries (GBs). Our results reveal that there are significant variations in SBH at atoms in the defected heterojunctions. Of particular interest is the fact that the SBH in some areas with extended defects approaches zero, indicating Ohmic contact. One important implication of this finding is that the effective SBH should be intrinsically dependent on the defect density and character. Remarkably, the obtained effective SBH values demonstrate good agreement with existing experimental measurements. Thus, the present study addresses two long-standing challenges associated with SBH in MoS2-metal heterojunctions: the wide variation in experimentally measured SBH values at MoS2@metal heterojunctions and the large discrepancy between density-functional-theory-predicted and experimentally measured SBH values. Our proposed approach points out a valuable pathway for understanding and manipulating SBHs at metal-semiconductor heterojunctions.

The manipulation of rectifying contact of Co and nitrogen‐doped carbon hierarchical superstructures toward high‐performance oxygen reduction reaction

AbstractRational design and construction of oxygen reduction reaction (ORR) electrocatalysts with high activity, good stability, and low price are essential for the practical applications of renewable energy conversion devices, such as metal‐air batteries. Electronic modification through constructing metal/semiconductor Schottky heterointerface represents a powerful strategy to enhance the electrochemical performance. Herein, we demonstrate a concept of Schottky electrocatalyst composed of uniform Co nanoparticles in situ anchored on the carbon nanotubes aligned on the carbon nanosheets (denoted as Co@N‐CNTs/NSs hereafter) toward ORR. Both experimental findings and theoretical simulation testify that the rectifying contact could impel the voluntary electron flow from Co to N‐CNTs/NSs and create an internal electric field, thereby boosting the electron transfer rate and improving the intrinsic activity. As a consequence, the Co@N‐CNTs/NSs deliver outstanding ORR activity, impressive long‐term durability, excellent methanol tolerance, and good performance as the air‐cathode in the Zn‐air batteries. The design concept of Schottky contact may provide the innovational inspirations for the synthesis of advanced catalysts in sustainable energy conversion fields.

Design Strategy of Vertical GaN Power Schottky Barrier Diodes with p‐GaN Junction Termination Extension and Experimental Demonstration of Selective p‐Doping by Implantation

Design Strategy of Vertical GaN Power Schottky Barrier Diodes with p‐GaN Junction Termination Extension and Experimental Demonstration of Selective p‐Doping by Implantation

Failure analysis of heavy ion-irradiated silicon carbide junction barrier Schottky diodes

An analysis of damage, including single event burnout (SEB) and single event leakage current (SELC) caused by heavy ion irradiation in silicon carbide (SiC) junction barrier Schottky diodes (JBSDs), was performed using Auger electron spectroscopy (AES), emission microscope (EMMI), focused ion beam (FIB), transmission electron microscopy (TEM) and other methods. The damage of SEB extending from the Schottky contact through the epitaxial layer to the SiC substrate was observed. The damage causing SELC was related to the micro-burnout of the Schottky contact. It was concluded that the damage of Schottky contact was induced by incident high-energy particles under a large electric field, forming a leakage current path, resulting in SEB and SELC in the SiC device.

Lanthanum(III)hydroxide Nanoparticles and Polyethyleneimine-Functionalized Graphene Quantum Dot Nanocomposites in Photosensitive Silicon Heterojunctions.

Lanthanides are largely used in optoelectronics as dopants to enhance the physical and optical properties of semiconducting devices. In this study, lanthanum(III)hydroxide nanoparticles (La(OH)3NPs) are used as a dopant of polyethylenimine (PEI)-functionalized nitrogen (N)-doped graphene quantum dots (PEI-NGQDs). The La(OH)3NPs-dopedPEI-NGQDs nanocomposites are prepared from La(NO)3 in a single step by a green novel method and are characterized by Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Deposited over an n-type Si wafer, the La(OH)3NPs-dopedPEI-NGQDs nanocomposites form Schottky diodes. The I-V characteristics and the photoresponse of the diodes are investigated as a function of the illumination intensity in the range 0-110 mW cm-2 and at room temperature. It is found that the rectification ratio and ideality factor of the diode decrease, while the Schottky barrier and series resistance increase with the enhancing illuminations. As a photodetector, the La(OH)3NPs-dopedPEI-NGQDs/n-Si heterojunction exhibits an appreciable responsivity of 3.9 × 10-3 AW-1 under 22 mW cm-2 at -0.3 V bias and a maximum detectivity of 8.7 × 108 Jones under 22 mW cm-2 at -0.5 V. This study introduces the green synthesis and presents the structural, electrical, and optoelectronic properties of La(OH)3NPs-dopedPEI-NGQDs, demonstrating that these nanocomposites can be promising for optoelectronic applications.

Study of optical float-zone grown gallium oxide Schottky barrier diode

β−Ga2O3 based lateral Schottky barrier diodes are fabricated using Ni/Au as Schottky contact and Ti/Au as Ohmic contact. The Sn-doped β−Ga2O3 sample is grown by the optical float-zone technique. The effect of trenches, which are used for mesa isolation, on breakdown voltage is investigated. The device shows near-ideal characteristics in terms of built-in potential. The parasitic series and shunt resistances are extracted, and their dependency on temperature is established. Modeling of temperature-dependent reverse leakage current is demonstrated using the thermionic emission model, Poole–Frenkel emission model, and Fowler-Nordheim tunneling mechanism. The procedure to extract relevant parameters is explained in terms of bias and temperature dependency. The combined model shows excellent agreement with experimental data over a wide range of bias and temperature. The maximum electric field of 2.3 MV cm−1 is achieved.

Ge doping of α-Ga2O3 thin films via mist chemical vapor deposition and their application in Schottky barrier diodes

We performed Ge doping of α-Ga2O3 thin films grown on m-plane sapphire substrates using mist chemical vapor deposition. Although the typical growth rate was high at 4 μm/h, the resultant α-Ga2O3 thin films exhibited high crystallinity. We controlled the carrier density in the range of 8.2 × 1016–1.6 × 1019 cm−3 using bis[2-carboxyethylgermanium(IV)]sesquioxide as the Ge source. The highest mobility achieved was 66 cm2 V−1 s−1 at a carrier concentration of 6.3 × 1017 cm−3. Through secondary ion mass spectrometry analysis, a linear relationship between the Ge concentration in the α-Ga2O3 thin films and the molar ratio of Ge to Ga in the source solution was established. The quasi-vertical Schottky barrier diode fabricated using the Ge-doped α-Ga2O3 thin films exhibited an on-resistance of 7.6 mΩ cm2 and a rectification ratio of 1010. These results highlight the good performance of the fabricated device and the significant potential of Ge-doped α-Ga2O3 for power-device applications.

Investigating the impact of physical vapour deposition of palladium on electron-irradiated silicon substrates

This study reports on the effect of resistive physical vapour deposition of Pd Schottky contacts on the defects observed in an irradiated n-type Si substrate. Deep-level transient spectroscopy (DLTS) was used in order to investigate the possible defects in Schottky diodes on the n-type Si. In this study the defects present where the diode was deposited first and then irradiated (“post irradiated”) were compared to those present where the substrate was irradiated first, and the Pd deposited after irradiation (“pre-irradiated”). In the post-irradiated material, the familiar radiation-induced defects were observed. However, in the pre-irradiated material, fourteen new defects were observed, with DLTS signatures differing from those of the defects in the post-irradiated diodes. The newly identified defects seemed to be specifically caused by the deposition of Pd contacts after irradiation of the substrate, as these defects were not observed when other metals such as Au, Ni, Al and Ag were deposited after irradiation. In this paper, we will refer to the observed effect that Pd deposition replaced the familiar radiation-induced defects in Si with the new set of defects as the “Pd effect”. Careful experiments ruled out annealing due to inadvertent heating of the sample during deposition as a possible cause. Care was taken to avoid all sources of contamination: The effect was observed for different sources of Pd and crucibles. This effect was inhibited by the presence of a thin intermediate layer of Pd or Au deposited before irradiation. We therefore conclude that the effect is only observed when Pd is deposited directly onto the irradiated Si surface. Out of the fourteen newly observed defects, four defects, with activation energy of 182, 220, 360 and 607 meV, had DLTS signatures corresponding to those of defects previously observed in Pd-containing Si. For the rest of the defects, no defects with similar DLTS signatures were found in literature. We therefore believe that the defects observed are produced by defect enhanced diffusion of Pd. Overall, the study enhances our understanding of defect behaviour in silicon-based devices, particularly under irradiation and metal deposition conditions, and reveals the unique properties and effects of Pd.

BDAPbI4 Dion Jacobson hybrid perovskite-based artificial nociceptors on biodegradable substrate

With the current evolution in artificial intelligence technology, biodegradable biomimetic devices are essential to execute increasingly complicated tasks and respond to challenging work environments. Consequently, the integration of artificial nociceptors holds considerable importance in enhancing the capabilities of humanoid robots. Low-dimensional Hybrid organic–inorganic Perovskites (HOIPs) show promise in emulating biological neurons owing to their inherent ion migration properties. In this work, we present Dion-Jacobson hybrid perovskite (BDAPbI4 (BDA=NH3C4H8NH3)) diffusive memristor on a paper substrate to serve as an artificial nociceptor. The symmetric electrode configuration as Paper/Ag/PCBM/BDAPbI4/PMMA/Ag demonstrates low operating voltage diffusive memristor with an ON/OFF ratio of ∼103. The surface investigation of device before top electrode deposition via X-ray photoelectron spectroscopy XPS and electrical characteristics of the complete device reveal the interplay between Schottky barrier at BDAPbI4/Ag interface and conductive filament formation/rupture within active layer as the origin of the abrupt resistive switching. The characteristics of the diffusive memristor resemble those of biological nociceptors, displaying sensitivity to external stimuli and key attributes such as threshold response, lack of adaptation, and relaxation. These findings underscore the potential application of Dion-Jacobson hybrid perovskites (BDAPbI4) as diffusive memristors in future neuromorphic intelligence systems.

Thermal annealing effect on phase evolution, physical properties of DC sputtered copper oxide thin films and transport behavior of ITO/CuO/Al Schottky diodes

Herein, we report on the post-annealing temperature effect on the transport behavior of p-CuO/Al Schottky barrier diodes. In addition, the transformation of phase from Cu4O3 to CuO phase was studied. Copper oxide thin films were grown on soda lime glass substrates, and post-annealing temperature's influence on the films’ structural, chemical, morphological, and electrical characteristics was comprehensively examined. X-ray diffraction study revealed the development of polycrystalline tenorite phase (CuO) on annealing. Raman analysis also confirmed the formation of the tenorite phase (CuO) at higher annealing temperatures (400 °C and 500 °C). XPS study revealed the occurrence of the Cu4O3 phase for room temperature deposited sample and CuO phase at the higher annealing temperature. Using current–voltage analysis, the Chueng model, and the thermoelectric emission model, the Schottky behavior between the metal and semiconductor were investigated. The fabricated diode showed a rectification ratio of 103 at ± 2 V, with the barrier height ranging from 0.84 to 1.12 eV due to different annealing treatments. The attributes of the power law were employed to elucidate space charge-limited conduction and the process of tunneling across the density of interface traps in p-CuO/Al Schottky diodes. This study provides valuable insights into the behavior of the p-CuO/Al Schottky junction, enhancing our understanding of its characteristics.

Lexible sensors for food monitoring. Part II: Applications

Monitoring and maintaining food quality, safety, and authenticity are the most important concerns in the food industry. The cutting-edge flexible sensors for food monitoring precisely satisfy the needs of acquiring information on multiple parameters in a small space, they provide for the more reasonable layout, get data on the mechanical deformations, and can be conformably attached to arbitrarily curved surfaces. The flexible sensing materials with a large area of specific surface, that ensure high mobility and density of the media, feature dense active sites, outstanding adjustability and high processing capacities, such as two-dimensional carbon nanomaterials, conductive polymers, and nano-hybrid materials; those materials have further improved the sensitivity, stability and selectivity of the flexible sensors’ perception. This article attempts to critically review the present state-of-arts developments in relation to the materials, manufacturing techniques and sensing mechanisms of the devices, as well as the applications of the electrically-transduced flexible sensors. Moreover, this article elaborates on the transduction mechanisms of the several typical transducers, with a focus on the physics behind, including the modulation of the doping level, Schottky barrier, and interfacial layer that typically cause changes in conductivity, functionality and permittivity. We also highlight the benefits and the technical challenges along with the appropriate solutions provided by the presented flexible sensors, and we also consider the potential strategies that allow overcoming limitations in power consumption, quantitatively assess the trade-offs in maintaining the quality and marketability, to optimize wireless communication and explore new sensing patterns.

Exploring the influence of the contact resistance on perovskite phototransistors

Organic–inorganic hybrid perovskites are widely used in photodetection owing to their high optical absorption coefficients. A variety of research has been conducted on perovskite phototransistors and their optoelectronic properties, but the exploration of the influence of contact resistance remains limited. In this work, we employed the transmission-line method to separate the contact resistance Rc × W (ranging from 4.81 × 104 to 4.77 × 103 Ω cm) and the channel resistance Rch × W (ranging from 1.93 × 104 to 1.16 × 104 Ω cm) of (PEA)2SnI4 perovskite phototransistors at different light intensities (520 nm, ranging from 0 to 2550 μW/cm2). Further analysis reveals that illumination-induced accumulation of charge carriers at the metal/semiconductor interface reduces the Schottky barrier. Approximately 90% of the observed increase in photocurrent can be attributed to the reduction in the contact resistance. Our finding underscores the crucial role of charge injection in influencing perovskite-based phototransistors.

Tailoring the morphology and charge transfer pathways of ultrathin Cd0.8Zn0.2S nanosheets via ionic liquid-modified Ti3C2 MXenes towards remarkable photocatalytic hydrogen evolution

Small-sized CdxZn1–xS solid solution nanomaterial is an important candidate for efficient photocatalytic hydrogen evolution (PHE), but it still suffers from easy agglomeration, severe photo corrosion, and fast photogenerated electron-hole recombination. To tackle these issues, herein, we propose a new strategy to modify CdxZn1–xS nanoreactors by the simultaneous utilization of ionic-liquid)-assisted morphology engineering and MXene-incorporating method. That is, we designed and synthesized a novel hierarchical Cd0.8Zn0.2S/Ti3C2 Schottky junction composite through the in-situ deposition of ultrathin Cd0.8Zn0.2S nanosheets on unique IL-modified Ti3C2 MXenes by a one-pot solvothermal method for efficiently PHE. The unique construction strategy tailors the thickness of ultrathin Cd0.8Zn0.2S nanosheets and prevents them from stacking and agglomeration, and especially, optimizes their charge transfer pathways during the photocatalytic process. Compared with pristine Cd0.8Zn0.2S nanosheets, Cd0.8Zn0.2S/Ti3C2 has abundant photogenerated electrons available on the Ti3C2 surface for proton reduction reaction, owing to the absence of deep-trapped electrons, suppression of electron-hole recombination in Cd0.8Zn0.2S and high-efficiency charge separation at the Cd0.8Zn0.2S/Ti3C2 Schottky junction interface. Moreover, the hydrophilicity, electrical conductivity, visible-light absorption capacity, and surficial hydrogen desorption of Cd0.8Zn0.2S/Ti3C2 heterostructure are significantly improved. As a result, the heterostructure exhibits outstanding photocatalytic stability and super high apparent quantum efficiency, being rendered as one of the best noble-metal-free Cd-Zn-S-based photocatalysts. This work illustrates the mechanisms of morphology control and heterojunction construction in controlling the catalytic behavior of photocatalysts and highlights the great potential of the IL-assisted route in the synthesis of high-performance MXene-based heterostructures for photocatalytic hydrogen evolution.

Oxygen vacancy-enrich Ag/brookite TiO2 Schottky junction for enhanced photocatalytic CO2 reduction

Insufficient surface catalytic sites and charge kinetics constrains the progress of CO2 photoreduction reaction. In this work, oxygen vacancy-enriched Ag/brookite TiO2 hybrid by anchoring Ag nanoparticles on brookite TiO2 has been synthesized through the transformation of Ti-glycerol precursor with simultaneous reduction of Ag+ in the diethylene glycol (DEG)-H2O solution. In particular, the involving of oxygen vacancy and Ag species could extend light absorption range, facilitate charge separation and transfer, and accumulate the electrons on Ag center. As a result, the Ag/brookite TiO2 with formed Schottky junction reveals enhanced CO2 photoreduction performance compare with pristine TiO2 and solvothermal treated TiO2 (TiO2-sol). Particularly, the oxygen vacancy-enriched Ag/TiO2 hybrid shows the highest catalytic activity with CH4 and CO yields. This work offers an approach to modify brookite phase TiO2 with metallic sites and oxygen vacancy for improved CO2 photoreduction.

Facet-dependent in-situ formation of oxygen vacancy and plasmonic Bi in BiOBr nanosheets and resultant influence on the generation and separation of charge carriers

The development of advanced photoactive materials has aroused widespread interest, but is severely plagued by the inherent narrow photo-responsive range and rapid recombination of electrons and holes. In this study, the unconventional BiOBr nanosheets decorated with Bi0 and oxygen vacancies (OVs) are successfully synthesized through a facial one-pot hydrothermal method, followed by heat treatment. Cetyltrimethylammonium bromide and mannitol contribute to the selective exposure of (001) and (010) facets, respectively. The absence of the outermost Br atoms facilitates the simultaneous generation of OVs and Bi0 on the surface during heating, forming the Schottky junction. The synergy of SPR in the Bi0 metal, OVs and Schottky junction can effectively enhance the light absorption and charge separation. This work proposes and verifies a feasible approach to construct defects in-situ by regulating the crystal facets and manipulating the surface atomic arrangement and coordination.

On the temperature dependence of the current conduction mode in non-homogeneous Pt/n-GaN Schottky barrier diode

Forward current-voltage (I–V) measurements of Pt/n-GaN Schottky barrier diode (SBD) are investigated in a wide temperature range (80–400 K). The temperature dependence of the effective Schottky barrier height (SBH) and ideality factor are analyzed on the basis of the thermionic emission (TE) model by considering a double Gaussian distribution (DGD) of SBH due to the presence of barrier height inhomogeneities at the Pt/n-GaN interface. In the high temperature (HT) region (200–400 K), Pt/n-GaN SBD exhibits nearly an ideal behavior in accordance with the TE conduction mode. The obtained values of the homogeneous SBH Φ‾0bn = 1.33 eV and Richardson constant AHT* = 26.86 A cm−2 K−2are in agreement with the theoretical values for n-type GaN. In the low temperature (LT) region (80–160 K), the corresponding values Φ‾0bn = 0.94 eV and ALT* = 14.74 A cm−2 K−2 deduced within the TE mode deviate strongly from the ideal behavior. This deviation is further confirmed by the large ideality factor. In this work, we provide a strong evidence that the tunneling current including thermionic field emission (TFE) largely dominates the conduction mode at low temperature.

Machine Learning to Promote Efficient Screening of Low-Contact Electrode for 2D Semiconductor Transistor Under Limited Data.

Low-barrier and high-injection electrodes are crucial for high-performance (HP) 2D semiconductor devices. Conventional trial-and-error methodologies for electrode material screening are impractical because of their low efficiency and arbitrary specificity. Although machine learning has emerged as a promising alternative to tackle this problem, its practical application in semiconductor devices is hindered by its substantial data requirements. In this paper, a comprehensive scheme combining an autoencoding regularized adversarial neural network and a feature-adaptive variational active learning algorithm for screening low-contact electrode materials for 2D semiconductor transistors with limited data is proposed. The proposed scheme exhibits exceptional performance by training with only 15% of the total data points, where the mean square errors are 0.17 and 0.27eV for the vertical and lateral Schottky barrier, respectively, and 2.88% for tunneling probability. Further, it exhibits an optimal predictive performance for 100 randomly sampled training datasets, reveals the underlying physical insight based on the identified features, and realizes continual improvement by employing detailed density-of-states descriptors. Finally, the empirical evaluations of the transport characteristics are conducted and verified by constructing MOSFET devices. These findings demonstrate the considerable potential of machine-learning techniques for screening high-efficiency electrode materials and constructing HP 2D semiconductor devices.

Neutron irradiation and polarization effect of 4H–SiC Schottky detector

Neutron irradiation experiments were carried out on a 4H–SiC Schottky detector. The effects of neutron and accompanying γ-rays irradiation on the electrical properties, charge collection efficiency (CCE), energy resolution and crystal defects of 4H–SiC detectors were investigated. The total irradiation fluence was 1.24 × 1014 n/cm2, with an equivalent 1 MeV neutron fluence of 1.33 × 1015 n/cm2. Following neutron irradiation, the turn-on voltage increased significantly, and the capacitance of the Schottky junction no longer varied with the reverse bias voltage. The CCE of the detector decreased from 100% to 90.8%, while the energy resolution increased from 0.79% to 1.49%. The irradiated detector required a higher bias voltage for optimal performance. Additionally, we observed two defect levels, Ec-0.5 eV and Ec-0.35 eV, in the 4H–SiC crystals after irradiation. Their generation is also related to gamma ray irradiation. The detector exhibited a polarization effect, where the energy spectrum split into two distinct components during prolonged measurement of monoenergetic α particles. The peak position gradually shifted towards the lower energy side with increasing testing time. These effects can be mitigated by increasing the bias voltage to enhance the electric field strength in the drift region.