Increase In Barrier Height Research Articles

Rectifying Characteristics of the Perovskite Oxide La1−xSrxMnO3/Nb‐0.7 wt%‐Doped SrTiO3 Heterojunction

The influence of Sr‐doping on the rectifying characteristics of the perovskite oxide La1−xSrxMnO3/Nb‐0.7 wt%‐doped SrTiO3(LSMO/NSTO) heterojunction is studied systematically. Clear rectification characteristics are observed in the Au/LSMO/NSTO heterojunction with Sr‐doping rate of 0.1–0.6 at 300 K. The threshold voltage and Schottky barrier height increase linearly with the increase in Sr‐doping. Combined with first‐principles calculations, it is found that the variation of Sr‐doping concentration directly leads to a change in the LSMO work function, then a change in barrier height, and finally a change in the threshold voltage and rectification characteristics. Ultimately, it is proved that the rectification characteristics of the perovskite metal oxide heterostructure are consistent with the potential barrier mechanism of semiconductors. The rectifying characteristics of the perovskite oxide p–n junction can be well modulated by the change in energy band structure caused by Sr‐doping. These results lay a foundation for further understanding of the rectification characteristics of the perovskite oxide heterostructure and improving its application value.

Primordial black holes and gravitational waves from resonant amplification during inflation

We present a new realization of the resonant production of primordial black holes as well as gravitational waves in a two-stage inflation model consisting of a scalar field \phi with an axion-monodromy-like periodic structure in the potential that governs the first stage and another field \chi with a hilltop-like potential that dominates the second stage. The parametric resonance seeded by the periodic structure at the first stage amplifies the perturbations of both fields inside the Hubble radius. While the evolution of the background trajectory experiences a turn as the oscillatory barrier height increases, the amplified perturbations of \chi remain as they are and contribute to the final curvature perturbation. It turns out that the primordial power spectrum displays a significant resonant peak on small scales, which can lead to an abundant production of primordial black holes. Furthermore, gravitational waves are also generated from the resonantly enhanced field perturbations during inflation, the amplitude of which may be constrained by future gravitational wave interferometers.

Analysis of Transfer Gate Doping Profile Influence on Dark Current and FWC in CMOS Image Sensors

The influence of transfer gate (TG) doping profile on dark current and full well capacity (FWC) has been investigated in this article. By analyzing the non-uniform doped TG channel in 4T pixel, a potential profile with a barrier is extracted at TG off state. In this analysis, twice P-type doping under TG directly determine the barrier position and its height. By adjusting the two P-type doping length under TG, dark current under TG is drained to floating diffusion instead of pinned photodiode, which is divided by the barrier. On the other hand, the increase of doping implantation under TG is beneficial to FWC due to the increased barrier height. Technology computer aided design (TCAD) simulations are performed to verify the analysis. Furthermore, a test chip with 6 μm × 6 μm pixels fabricated in a 0.11 μm CMOS process is tested. In our design, by shortening LTG_PD and extending LTG_FD, dark current reduces by 15% and 17%, respectively. In the case of a certain doping profile under TG, shorting the length of TG from 0.6 μm to 0.4 μm helps reduce dark current by 30% at the cost of 6% FWC reduction.

Temperature-Dependent Electrical Properties of Graphitic Carbon Schottky Contacts to β-Ga₂O₃

Graphitic (sp <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -rich) carbon Schottky contacts to (201) β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> were fabricated using sputtering and energetic ion deposition with and without the use of an oxygen plasma. As-deposited contacts exhibited room temperature effective barrier heights between 0.80 and 1.20 eV, depending on the deposition technique. After moderate heat treatment (595 K in N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) the work function of the oxygenated graphitic contacts increased by 0.5-0.8 eV. This resulted in a permanent increase in barrier height (up to 1.6 eV) and a corresponding 3-4 orders of magnitude increase in current rectification (at ±3 V). The barrier heights of the heat-treated oxygenated graphitic Schottky contacts agree well with the Mott-Schottky model, suggesting an absence of Fermi level pinning at the C/β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> interface.

Record-High-Performance Hydrogenated In-Ga-Zn-O Flexible Schottky Diodes.

High-performance In-Ga-Zn-O (IGZO) Schottky diodes (SDs) were fabricated using hydrogenated IGZO (IGZO:H) at a maximum process temperature of 150 °C. IGZO:H was prepared by Ar + O2 + H2 sputtering. IGZO:H SDs on a glass substrate exhibited superior electrical properties with a very high rectification ratio of 3.8 × 1010, an extremely large Schottky barrier height of 1.17 eV, and a low ideality factor of 1.07. It was confirmed that the hydrogen incorporated during IGZO:H deposition increased the band gap energy from 3.02 eV (IGZO) to 3.29 eV (IGZO:H). Thus, it was considered that the increase in band gap energy (decrease in electron affinity) of IGZO:H contributed to the increase in the Schottky barrier height of the SDs. Angle-resolved hard X-ray photoelectron spectroscopy analysis revealed that oxygen vacancies in IGZO:H were much fewer than those in IGZO, especially in the region near the film surface. Moreover, it was found that the density of near-conduction band minimum states in IGZO:H was lower than that in IGZO. Therefore, IGZO:H played a key role in improving the Schottky interface quality, namely, the increase of Schottky barrier height, decrease of oxygen vacancies, and reduction of near-conduction band minimum states. Finally, we fabricated a flexible IGZO:H SD on a poly(ethylene naphthalate) substrate, and it exhibited record electrical properties with a rectification ratio of 1.7 × 109, Schottky barrier height of 1.12 eV, and ideality factor of 1.10. To the best of our knowledge, both the IGZO:H SDs formed on glass and poly(ethylene naphthalate) substrates achieved the best performance among the IGZO SDs reported to date. The proposed method successfully demonstrated great potential for future flexible electronic applications.

Mechanical relaxation in amorphous selenium

Literature mechanical relaxation data of amorphous selenium are interpreted in terms of the soft potential model and its extension to higher temperatures, the Gilroy-Phillips model. At the crossover temperature from tunneling states to thermally activated relaxation, one finds a stronger decrease of the barrier density f(V) with increasing barrier height V than in silica. On the high barrier side, f(V) is determined by the Kohlrausch t β -tail of the viscous flow, with β = 0.31. In longitudinal ultrasound absorption data, one finds weak oscillations of the Kohlrausch barrier density, similar to those found recently in metallic glasses, consistent with an increase of the barrier by V 1 = S 1 T g /β for the addition of one selenium atom to the rearranging domain, where S 1 is the structural entropy per atom at the glass temperature T g .

Temperature dependence of electrical parameters of the Cu/n-Si metal semiconductor Schottky structures

The main electrical characteristics of Cu/n-Si metal-semiconductor structures have been investigated in the temperature range 50 K to 310 K using current–voltage (I–V) and capacitance–voltage (C–V) measurements. It has been showed that the values of ideality factor and barrier height increase with increase in temperature and are clarified by invoking three different set of Gaussian distributions (GD) of barrier height at 50–160 K, 160–220 K, and 220–310 K. The values of ideality factor and barrier height for the Cu/n-Si metal-semiconductor structures were obtained as 1.435 and 0.487 eV at 50 K, 1.399 and 0.704 at 120 K, 2.192 and 0.701 at 220 K, and 4.286 and 0.759 eV at 310 K, respectively. This results showed fairly that in presence of inhomogeneity at metal semiconductor (MS) interface. The double Gaussian distribution of the temperature dependent I–V characteristics of the Cu/n-Si metal-semiconductor structures barrier diode gave the mean barrier heights of 0.532, 0.638 and 0.816 eV and standard deviations (σo) of 3120 mV, 37 mV and 53 mV, respectively. Thus, the values of the mean barrier height have been verified with the modified ln(I0/T2)−q2σ2/2k2T2 versus (kT)−1 plot which belongs the three different temperature regions. Furthermore, it was showed that a noticeable increase of the saturation current from 1.978 × 10–46 to 3.973 × 10–8 A, (from 50 K to 310 K). The increase in saturation current after temperature was attributed to the presence of interface states created by temperature induced defects.

Investigation of Barrier Inhomogeneities and Electronic Transport on Al-Foil/p-Type-4H-SiC Schottky Barrier Diodes Using Diffusion Welding

The diffusion welding (DW) is a comprehensive mechanism that can be extensively used to develop silicon carbide (SiC) Schottky rectifiers as a cheaper alternative to existing mainstream contact forming technologies. In this work, the Schottky barrier diode (SBD) fabricated by depositing Al-Foil on the p-type 4H-SiC substrate with a novel technology; DW. The electrical properties of physically fabricated Al-Foil/4H-SiC SBD have been investigated. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics based on the thermionic emission model in the temperature range (300 K–450 K) are investigated. It has been found that the ideality factor and barrier heights of identically manufactured Al-Foil/p-type-4H-SiC SBDs showing distinct deviation in their electrical characteristics. An improvement in the ideality factor of Al-Foil/p-type-4H-SiC SBD has been noticed with an increase in temperature. An increase in barrier height in fabricated SBD is also observed with an increase in temperature. We also found that these increases in barrier height, improve ideality factors and abnormalities in their electrical characteristics are due to structural defects initiation, discrete energy level formation, interfacial native oxide layer formation, inhomogenous doping profile distribution and tunneling current formation at the SiC sufaces.

Impact of Implanted Edge Termination on Vertical β-Ga2O3 Schottky Barrier Diodes Under OFF-State Stressing

Both dc and OFF-state stress characteristics of vertical beta-gallium oxide (β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) Schottky barrier diodes (SBDs) with or without ion-implanted edge termination (ET) were comparatively analyzed in this work. An implanted ET by He and Mg ions can effectively increase breakdown voltage (BV) from 0.5 to 1.0 and 1.5 kV, respectively, by sacrificing minimal forward characteristics. However, SBDs with ion ET exhibited a larger degradation than SBDs without ion ET after OFF-state stressing, especially for Mg ion-implanted ET, which caused more severe lattice damage at the edge of the anode by transmission electron microscopy (TEM) verification. The OFF-state characteristics were investigated by conventional measure/stress/measure (MSM) with reverse stress biases applied from -100 to -1000 V. The ion-implanted ET brings two effects on the device characteristics: 1) the increase of Schottky barrier height (φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) in both dc and OFF-state stress characteristics caused by the virtual gate-like effect and leading to an increased V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> and 2) the increase of R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON,SP</sub> in the forward dc characteristics is attributed to the increase of anode resistance and lateral depletion.

Coherence effects of the strongly-coupled optical polaron-level qubit in a quantum well with asymmetrical semi-exponential potential

Abstract A theoretically investigation of the effects of barrier height of an asymmetrical semi-exponential confinement potential (ASECP) quantum well (QW) and the range of the ASECP on vibration frequency, first excited state (FES) energy, excitation energy and coherence time in the ASECP QW is performed. In order to determine the relationship between these factors, the linear combination operator, twice unitary transformations and Fermi Golden Rule methods are used. The vibration frequency, FES energy and excitation energy of the strong-coupled polaron are derived, as well as the qubit coherence time in the ASECP QW when the barrier height of the QW and the ASECP range are varied. It is found that these physical quantities are increasing functions of the barrier height, whereas they are decaying functions of the range. Furthermore, the coherence time is a decaying function with increased barrier height and an increasing function with enhanced range.

Modulating Schottky barrier of metal/p-type 4H-SiC by thin insulator TiO2 layer intercalation

We have investigated the barrier modulation of an electrically homogeneous Ni/p-type 4H-SiC contact by intercalation of a thin insulator TiO2 layer. It is found that the TiO2 layer can provide an extra barrier increase, resulting into the barrier height at the interface exceeding the Schottky–Mott limit. However, the barrier is inhomogeneous and Gaussianly distributed over the contact area. The barrier inhomogeneity may be due to an increase in interface states density caused by the oxide induced traps. The increase in barrier height is believed to originate from an electrostatic potential increase across the dipole layer related to the induced positive polarization charges on the p-type 4H-SiC surface.

Tuning the Schottky barrier height in graphene/monolayer-GeI2 van der Waals heterostructure

We use first-principles simulations to investigate the structural and electronic properties of a heterostructure formed by graphene and monolayer GeI2 (m-GeI2). While graphene has been extensively studied in the last 15 years, m-GeI2 has been recently proposed to be a stable 2D semiconductor with a wide-band gap, Liu et al (2018 J. Phys. Chem. C 122 22137). By staking both structures we obtain a metal-semiconductor junction, with great potential for applications in the designing of new (opto)electronic devices. The results show that the graphene Dirac cone is preserved in the graphene/m-GeI2 heterostructure. We find that there are no chemical bonds at the graphene and m-GeI2 interface, thus the heterostructure interactions are ruled by van der Waals (vdW) forces. The interface between graphene and m-GeI2 results in a n-type Schottky contact. Furthermore, we show that a transition from n-type to p-type Schottky contact can be obtained by decreasing the interlayer distance. We also modulated the Schottky barrier heights by applying a perpendicular external electric field through the vdW heterostructure. In particular, positive values resulted in an increase of the n-type Schottky barrier height, while negative electric field values induced a transition from n-type to p-type Schottky contact. From our results, we show that m-GeI2 is an interesting material to design new electronic Schottky devices based on graphene vdW heterostructures.

Conductance Deep-Level Transient Spectroscopy and Current Transport Mechanisms in Au|Pt|n-GaN Schottky Barrier Diodes

The current transport mechanisms in Au|Pt|n-GaN Schottky barrier diodes are investigated in a temperature range of 40–325 K. The calculated barrier height and ideality factor are 1.12 and 2.13 eV, respectively, and it is observed that the barrier height Φb increases and the ideality factor n decreases with temperature increase. The apparent barrier height and the ideality factor derived by using thermionic emission theory are found to be strongly temperature-dependent. The increase in barrier height with increasing temperature has been explained as an effect of barrier inhomogeneity. This behavior has been interpreted based on the assumption of a Gaussian distribution of barrier heights due to barrier height inhomogeneity at the interface between the metal and semiconductor. The abnormal behavior of all these parameters can be attributed to the presence of deep levels thermally activated. Conductance deep-level transient spectroscopy (CDLTS) results shows that the two deep-level defects are observed in as-grown sample with activation energies of E1 = 0.18 eV and HL1 = 0.87 eV.

Increased radiative recombination of AlGaN-based deep ultraviolet laser diodes with convex quantum wells

An AlGaN-based deep ultraviolet laser diode with convex quantum wells structure is proposed. The advantage of using a convex quantum wells structure is that the radiation recombination is significantly improved. The improvement is attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes, which results in an increased hole injection efficiency and a decreased electron leakage into the p-type region. Particularly, comparisons with the convex quantum barriers structure and the reference structure show that the convex quantum wells structure has the best performance in all respects.

Ultrafast hot ion-exchange triggered electrocatalyst modification and interface engineering on silicon photoanodes

Slow charge transfer kinetics and poor stability are two critical issues for silicon (Si) photoanodes in photoelectrochemical (PEC) water splitting. Herein, a facile and ultrafast interfacial reaction was performed on n-Si/Ni for stable and high-performance Si photoanode by regulating both the Ni electrocatalyst and Si surface. The calculated and experimental results reveal that highly catalytic oxygen vacancies-rich Fe:NiOOH layer will be formed on Ni surface during the hot Fe ions exchange reaction, which can create abundant active sites for oxygen evolution reaction (OER). The interfacial reaction also can modulate the interfacial state of Si photoanode to increase barrier height for n-Si/Ni/Fe:NiOOH photoanode, thereby accelerating the charge separation and transportation. More significantly, a thin iron silicide (FeSi2) layer will be generated on Si surface (Ni-free region), which is beneficial for the stability of Si photoanode. This work provides a low-cost and straightforward approach to design high-performance Si photoanodes by interface engineering and electrocatalyst defects regulation.

Mechanically tuned conductivity at individual grain boundaries in polycrystalline ZnO varistor ceramics

Mechanically induced changes in electrical properties have gained increasing interest over the last decade. The research field piezotronics, which describes the change in potential barrier height (e.g., at Schottky contacts) by piezoelectric charges, could lead to promising applications such as sensors or strain trigged transistors. In this contribution, the changes of potential barriers by mechanical stress at several grain boundaries of polycrystalline ZnO have been quantified. Rationalization is provided by concurrent measurement of crystal orientations of both neighboring grains. The highest changes in barrier height could be observed at ZnO–ZnO grain boundaries exhibiting varistor properties. In this case, the barrier height can be almost completely reduced by positive piezoelectric charges. Furthermore, an increase in barrier height is observed with negative piezoelectric charges. The developed physical model suggests an equivalent impact of externally applied voltage and induced positive piezoelectric charge on the barrier properties. In turn, not only the barrier height is modified by piezoelectric charges but also the breakdown voltage. This has, nevertheless, been only indirectly verified in experiments. These allow rationalizing the proposed model. Furthermore, a statistical study reveals a change in the distribution of breakdown voltages with changing stress conditions in the varistor ceramic.

Investigation of current transport in Galfenol based Schottky diodes

We demonstrate for the first time Galfenol (FeGa) alloy in a ferromagnetic/semiconductor Schottky diode configuration with n-Si substrates. Electrical properties have been studied using current vs. voltage (I-V) and capacitance vs. voltage (C-V) measurements. The Schottky contact was fabricated by depositing a thin layer of FeGa onto n-Si substrates by radio frequency magnetron sputtering. Diode parameters in accordance with thermionic emission theory, such as ideality factor, barrier height and series resistance were extracted from the forward bias semi logarithmic I-V graph and were found to be 2.57, 0.76 eV and 43.25 kΩ respectively at room temperature. The corresponding values when calculated from dV/d(ln(I)) vs. I plot and Cheung functions were found to be 2.28, 0.74 eV and 43.2 kΩ respectively. Barrier height obtained using C-V measurement was found to be 0.77 eV which is close to the other two measurements. The increase in ideality factor and barrier height can be attributed to formation of a native interfacial oxide layer and inhomogeneity in barrier formation. Mixed type of conduction has been inferred from double logarithmic plots. Rectifying nature of the contact has been investigated by using the diode in half-wave rectifier configuration, testing the promise of a working Galfenol based device.

Optimizing Brownian escape rates by potential shaping

Brownian escape is key to a wealth of physico-chemical processes, including polymer folding and information storage. The frequency of thermally activated energy barrier crossings is assumed to generally decrease exponentially with increasing barrier height. Here, we show experimentally that higher, fine-tuned barrier profiles result in significantly enhanced escape rates, in breach of the intuition relying on the above scaling law, and address in theory the corresponding conditions for maximum speed-up. Importantly, our barriers end on the same energy on which they start. For overdamped dynamics, the achievable boost of escape rates is, in principle, unbounded so that the barrier optimization has to be regularized. We derive optimal profiles under 2 different regularizations and uncover the efficiency of N-shaped barriers. We then demonstrate the viability of such a potential in automated microfluidic Brownian dynamics experiments using holographic optical tweezers and achieve a doubling of escape rates compared to unhindered Brownian motion. Finally, we show that this escape rate boost extends into the low-friction inertial regime.

Superfluid fraction of few bosons in an annular geometry in the presence of a rotating weak link

We report a beyond mean-field calculation of mass current and superfluidity fraction for a system of few bosons confined in a ring geometry in the presence of a rotating weak link induced by a potential barrier. We apply the Multiconfiguration Hartree Method for bosons to compute the ground state of the system and show the average superfluidity fraction for a wide range of interaction strength and barrier height, highlighting the behavior of density correlation functions. The decrease of superfluidity fraction due to the increase of barrier height is found whereas the condensation fraction depends exclusively on the interaction strength, showing the independence of both phenomena.

MoSe2/graphene/6H-SiC heterojunctions: energy band diagram and photodegradation

The electronic and optoelectronic properties of van der Waals heterostructures are strongly affected by heterobarrier heights at the interfaces between monolayers forming the structure and the environment. In this work, properties of MoSe2/graphene/6H-SiC heterostructures are studied by scanning probe microscopy and photoluminescence spectroscopy in various ambient conditions. To improve our understanding of the electronic processes, a work function of the monolayer MoSe2 and its dependence on the number of layers were determined by Kelvin probe microscopy. A nonuniform distribution of the photoluminescence intensity from the MoSe2 monolayer was observed because of bilayer graphene (BLG) inclusions in the monolayer graphene (MLG) covering the 6H-SiC substrate. The measured values of the MoSe2 work function allow the construction of band energy diagrams for MoSe2/MLG and MoSe2/BLG heterobarriers, which show an increased barrier height for MLG with respect to BLG. This relatively high potential barrier at MoSe2/MLG leads to quenching of the photoluminescence because of separation of the electron–hole pairs at the barrier before the formation of the exciton. Moreover, selective photodegradation of the MoSe2 layers on MLG due to photooxidation during light illumination was observed. The photooxidation was promoted by accumulation of excess holes at the MoSe2/MLG interface, which further participate in splitting of a surface water film. Generation of the oxygen at the heterojunction interface leads to the oxidation of the MoSe2. The dependence of the photoluminescence and photodegradation of MoSe2 on the graphene layers shows the importance of the substrate selection for good device stability based on van der Waals heterostructures with MoSe2.