Properties Of Interface States Research Articles

Dynamic laser protection window based on a topological state photonic crystal of a nonlinear LiNbO3 interface.

The accelerated advancement of high-energy laser technology has resulted in an increased necessity for multifunctional laser protection. Herein, we present an investigation into a static visible and dynamic 1064 nm laser protection window. Through studying the photonic crystal energy band structure and topological interface state properties, both 66.49% average visible light transmittance and 84.01% low-energy 1064 nm laser transmittance are achieved. The combination of a large third-order nonlinear effect of LiNbO3 and strong light field localization of a topological interface state enables a 27.54 mJ/cm2 protection threshold below that of traditional materials. This study offers what we believe to be new avenues for the development of multifunctional optical windows and novel optical elements.

Interface states and optical coupling functionalities in the super-SSH lattices

We theoretically address the coupling between trimer lattices and reveal the existence of stable multiple edge and interface states. It is shown the superlattice can provides a tunable number of topologically protected edge and interface states depending on the coupling strength and topological phase of the connecting lattices. Dynamics and transport properties of interface states are also investigated, Due to the interference of linear modes with different propagation constants, stable oscillations resulted from the coupling of interface states in finite trimerized waveguide arrays are observed and can give rise to optical coupling functionalities, including directional coupling, beam splitting and beam oscillator.

Effect of carbon fiber surface treatment with HNO3 and KOH on the interfacial bonding of PMMA resin composite

Abstract This work studied the surface, interface state and physicochemical properties of HNO3-treated and KOH-treated carbon fiber. Poly(methyl methacrylate) (PMMA) composites were prepared by the autoclave molding process using surface-treated carbon fiber as reinforcements. The physical and chemical states of the carbon fiber surfaces and the micro-interface properties and interlaminar shear properties of the composites were studied. The results show that the surface of the HNO3-treated carbon fiber has more groove structure and higher surface roughness and thus forms a better physical bond with the resin matrix. Although the oxygen-containing functional groups of the two carbon fibers are equivalent, the surface oxygen of the HNO3-treated carbon fiber is relatively high, which is beneficial to form a better chemical bond with the matrix resin, and the interfacial shear strength is about 14% higher than that of the KOH-treated carbon fiber composite.

Research status and progress of metal contacts of SiC power devices

Silicon carbide (SiC) is a promising candidate for applications in high temperature, high voltage, high power, and low-power dissipation devices due to its unique properties like wide band gap, high critical electric field, and high thermal conductivity. However, one of the main bottlenecks hindering the SiC power devices from developing and being put into practical application is the fabrication of good metal/SiC contact. In this review, the research status of Ohmic contact and Schottky contact of SiC device are compared and analyzed. The complicated interface properties and uncontrollable barrier height at metal/SiC interface are revealed. In addition, the research status of metal/SiC contact barrier and interface state properties are analyzed, and the important significance of effective control of interface barrier is highlighted. Furthermore, the research progress of metal/SiC contact interface regulation technology is specially analyzed. The future development directions in the nature of metal/SiC interface states and interface control technology are finally prospected.

Insight into Al2O3/B-doped diamond interface states with high-temperature conductance method

We employed a high temperature conductance method to investigate the interface state properties of the Al2O3/B-doped diamond MOS structure by considering the surface potential fluctuation. Based on Gaussian approximation of Nicollian's model and Brew's graphical approach, we analyzed the frequency dependent characteristics of parallel conductance (Gp/ω–f) at various gate voltages and extracted the energy distribution of interface state density (Dit), capture cross section (σp), time constant (τit), and the standard deviation of surface potential fluctuation (σs). The Dit extracted by the conductance method exhibited good agreement with that by the high-low method, whereas there exist large errors when surface potential fluctuation was not considered by using the conductance method. The capture cross section extracted by the conductance method was on the order of 10−17 cm2. From the energy dependence of the interface state time constant, the hole capture and emission follow the Shockley–Read–Hall statistics. σs decreases with the energy position away from the valence band edge (Ev) of diamond, indicating that donor-like traps are distributed in the Ev side of diamond.

Role of metal contacts and effect of annealing in high performance 2D WSe2 field-effect transistors

Among the two dimensional (2D) transition metal dichalcogenides (TMDCs), tungsten diselenide (WSe2) have recently attracted much attention owing to its potential in CMOS technology, optoelectronics and high-speed device applications. One of the most challenging aspect in designing high performance devices is the metal-semiconductor interface. In this context, the potential of 2D materials even grows bigger because of their dangling-bond-free surface which leads to excellent interface quality. Additionally, the role of the contact metals also becomes very important as it explicitly determines the charge transport, carrier mobility, switching speed etc. In this work, WSe2 based field-effect transistors (FETs) were fabricated using different metal contacts such as Au (ϕm ∼ 5.47 eV) with Ti as adhesion layer, Mo (ϕm ∼ 4.53 eV) and Al (ϕm ∼ 4.08 eV). It was found that the charge transport properties in WSe2 changed from p-type (Au), then to ambipolar (Mo) and finally to n-type (Al) as work functions of the metals changed from high to low. Moreover, the effect of post-fabrication annealing was also studied, and it was found that the mobility increased up to ∼625 cm2/V-s, ∼410 cm2/V-s, and ∼366 cm2/V-s, for Au/Ti/WSe2, Mo/WSe2 and Al/WSe2 FETs respectively as a result of annealing. Finally, the interface properties were analyzed by determining the interface state densities Dit in the metal-2D WSe2 junctions and the values of Dit were found to decrease by an order of magnitude post-annealing treatment such as ∼4.65 × 1012 cm2 eV−1 for Au/Ti/WSe2, 1.08 × 1013 cm2 eV−1 for Mo/WSe2 and 2.28×1012 cm2 eV−1 for Al/WSe2 junctions. Our work shows the tunable charge transport properties in 2D WSe2 which is highly desirable for CMOS digital logic applications and the influence of annealing in improving the transport and interface state properties in 2D WSe2 FETs.

Lateral scattering potential of the PTCDA/Ag(111) interface state

A modified scheme of scanning tunneling spectroscopy data analysis has been used to reconstruct the band structure of a strongly dispersive two-dimensional unoccupied electronic state located at the commensurate interface between a monolayer of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) and Ag(111) surface up to the fourth band in the reduced Brillouin zone of the molecular monolayer. The two-dimensional scattering potential, evaluated with the help of the measured band structure data, is highly corrugated. This shows that the accepted picture, describing the interface state of PTCDA/Ag(111) as an upshifted Shockley state of Ag(111), is incomplete. Our findings indicate that the hybridization of unoccupied molecular orbitals of PTCDA on one of the two sublattices with the metal states of Ag(111) substantially influences the interface state properties.

Study of CBD-CdS/CZTGSe solar cells using different Cd sources: behavior of devices as a MIS structure

CdS buffer layer plays an important role in thin film solar cells; as a result, a deep understanding of its physical properties and impact on solar cell performance is highly required. In this work, we report results on growth conditions of CdS thin films deposited by chemical bath method to be used as insulators in MIS structure instead of the traditionally assumed p–n junction. Three different Cd sources—CdCl2, Cd(NO3)2, and CdSO4—are considered for CdS processing. The impact of Cd source on CdS physical properties as well as on the electro-optical device properties of CdS/CZTGSe solar cells is evaluated. Furthermore, interface state properties are calculated as a function of temperature. These states are a result of the CdS interaction with both the TCO and Kesterites, depending on the Cd source used in solution of the chemical bath deposition. Besides, some important requirements to be considered in order to improve device efficiency are discussed in the present work.

Quantum-mechanical study of tensorial elastic and high-temperature thermodynamic properties of grain boundary states in superalloy-phase Ni3Al

Grain boundaries (GBs), the most important defects in solids and their properties are crucial for many materials properties including (in-)stability. Quantum-mechanical methods can reliably compute properties of GBs and we use them to analyze (tensorial) anisotropic elastic properties of interface states associated with GBs in one of the most important intermetallic compounds for industrial applications, Ni3Al. Selecting the Σ5(210) GBs as a case study because of its significant extra volume, we address the mechanical stability of the GB interface states by checking elasticity-based Born stability criteria. One critically important elastic constant, C55, is found nearly three times smaller at the GB compared with the bulk, contributing thus to the reduction of the mechanical stability of Ni3Al polycrystals. Next, comparing properties of Σ5(210) GB state which is fully relaxed with those of a Σ5(210) GB state when the supercell dimensions are kept equal to those in the bulk we conclude that lateral relaxations have only marginal impact on the studied properties. Having the complete elastic tensor of Σ5(210) GB states we combine Green’s-function based homogenization techniques and an approximative approach to the Debye model to compare thermodynamic properties of a perfect Ni3Al bulk and the Σ5(210) GB states. In particular, significant reduction of the melting temperature (to 79-81% of the bulk value) is predicted for nanometer-size grains.

Spin to Charge Interconversion Phenomena in the Interface and Surface States

In 1985, Johnson and Silsbee realized the creation of a spin current in nonmagnetic metals, which inspired a vast number of studies related to the spin current until now. Creation of the spin current has been realized in metals, semiconductors, and insulators to date and has provided a fruitful research field. Spin-dependent conductance and spin torque paved a new way for spintronic application, and highly efficient interconversion between spin information and an industrially used one, such as charge current, light, magnetic moment and heat current, became a central topic. In the early stage, the main field of such interconversion was bulk materials; the focus then gradually shifted to surface and interface states. The properties of surface and interface states became pronounced in nanoscale spintronics devices, and a variety of functions have been realized at the interface between two materials, enabling limitless possibilities for spin functions. This review provides an overview of the recent progress o...

Electronic Properties of CdTe/CdS Solar Cells as Influenced by a Buffer Layer

ABSTRACTWe considered modification of the defect density of states in CdTe as influenced by a buffer layer in ZnO(ZnS, SnSe)/CdS/CdTe solar cells. Compared to the solar cells employing ZnO buffer layers, implementation of ZnSe and ZnS resulted in the lower net ionized acceptor concentration and the energy shift of the dominant deep trap levels to the midgap of CdTe. The results clearly indicated that the same defect was responsible for the inefficient doping and the formation of recombination centers in CdTe. This observation can be explained taking into account the effect of strain on the electronic properties of the grain boundary interface states in polycrystalline CdTe. In the conditions of strain, interaction of chlorine with the grain boundary point defects can be altered.

Time-reversal symmetry protected chiral interface states between quantum spin and quantum anomalous Hall insulators

We theoretically investigate the electronic properties of the interface between quantum spin Hall (QSH) and quantum anomalous Hall (QAH) insulators. A robust chiral gapless state, which substantially differs from edge states of QSH or QAH insulators, is predicted at the QSH/QAH interface using an effective Hamiltonian model. We systematically reveal distinctive properties of interface states between QSH and single-valley QAH, multivalley high-Chern-number QAH and valley-polarized QAH insulators based on tight-binding models using the interface Green's function method. As an example, first-principles calculations are conducted for the interface states between fully and semihydrogenated bismuth (111) thin films, verifying the existence of interface states in realistic material systems. Due to the physically protected junction structure, the interface state is expected to be more stable and insensitive than topological boundary states against edge defects and chemical decoration. Hence our results of the interface states provide a promising route towards enhancing the performance and stability of low-dissipation electronics in real environment.

Electrical parameters of Au/n-GaN and Pt/n-GaN Schottky diodes

Electrical properties of Si-doped GaN epitaxial layers, grown on a c-plane sapphire substrate by MOCVD to form Schottky diodes with Gold (Au) and platinum (Pt) and using Ti/Al/Au as Ohmic contact, are investigated. Characterization was performed through I–V and C–V–f measurements at room temperature. Schottky barrier height (Φb), ideality factor (n), and series resistance (Rs) were extracted from forward I–V characteriztics using Cheung and Lien methods. Φb, doping concentration (Nd) and Rs frequency dependence were extracted from C–V–f characteriztics. Pt/n-GaN shows a non-linear behavior with a barrier height of 0.63eV, an ideality factor of 2.3, and series resistance of 63Ω. Au/n-GaN behaves like two diodes in parallel with two barrier heights of (0.83 and 0.9eV), two ideality factors of (5.8 and 3.18) and two series resistance of (10.6 and 68Ω). Interface state properties in both samples have been investigated taking into account the bias dependence of the effective barrier height. The amount of stimulated traps along the energy-gap at the interface increases with voltage bias, which increases NSS exponentially from 4.24⋅1013 to 3.67⋅1014eV−1cm−2 in the range (Ec – 0.17) to (Ec – 0.61) eV for Pt/n-GaN, and from 2.3⋅1013 to 1.14⋅1014eV−1cm−2, in the range (Ec – 0.31) to (Ec – 0.82) eV for Au/n-GaN.The values of interface states density and series resistance for both samples are found to decrease with increasing frequency. Peak intensity was a measure of active interface states.C–V–f results confirm the model of the Schottky diode with a native interfacial insulator layer along the space charge region.

Evaluation of Accuracy of Charge Pumping Current in Time Domain

Accuracy of a method for analyzing the interface defect properties; time-domain charge pumping method, is evaluated. The method monitors the charge pumping (CP) current in time domain, and thus we expect that it gives us a noble way to investigate the interface state properties. In this study, for the purpose of evaluating the accuracy of the method, the interface state density extracted from the time-domain data is compared with that measured using the conventional CP method. The results show that they are equal to each other for all measured devices with various defect densities, demonstrating that the time-domain CP method is sufficiently accurate for the defect density evaluation.

Electron transport in asymmetric biphenyl molecular junctions: effects of conformation and molecule-electrode distance

On the basis of ab-initio calculations, we predict the effect of conformation and molecule-electrode distance on transport properties of asymmetric molecular junctions for different electrode materials M (M = Au, Ag, Cu, and Pt). The asymmetry in these junctions is created by connecting one end of the biphenyl molecule to conjugated double thiol (model A) and single thiol (model B) groups, while the other end to Cu atom. A variety of phenomena viz. rectification, negative differential resistance (NDR), switching has been observed that can be controlled by tailoring the interface state properties through molecular conformation and molecule-electrode distance for various M. These properties are further analyzed by calculating transmission spectra, molecular orbitals, and orbital energy. It is found that Cu electrode shows significantly enhanced rectifying performance with change in torsion angles, as well as with increase in molecule-electrode distances than Au and Ag electrodes. Moreover, Pt electrode manifests distinctive multifunctional behavior combining switch, diode, and NDR. Thus, the Pt electrode is suggested to be a good potential candidate for a novel multifunctional electronic device. Our findings are compared with available experimental and theoretical results.

Effect of thin gold interlayer on the electrical and dielectrical behaviors of ITO/MEH-PPV/Al structures

The effects of inserting a thin gold (Au) layer between the indium tin oxide (ITO) electrode and the poly [2-methoxy-5-(2-ethylhexyl-oxy)-p-phenylenevinylene] (MEH-PPV) organic material on the electrical and interface state properties of a ITO/MEH-PPV/Al device are investigated through current–voltage I(V), and capacitance–voltage characteristics C(V). The modified anode was characterized by atomic force microscope (AFM), and UV–vis transmittance spectra. The atomic force microscopy (AFM) surface roughness analysis indicates that a uniform and smoother surface is formed when the ITO is covered by the Au interlayer. A decrease in the transmittance and the optical band gap is observed in ITO/Au anode. The ITO/Au/MEH-PPV/Al device shows improved current density–voltage characteristics as compared with the ITO/MEH-PPV/Al. Diode parameters such as ideality factor, barrier height, series resistance and Shunt resistance are calculated using Schottky model corrected from the series and Shunt resistances. In the presence of the Au interlayer, the junction resistance across the ITO/MEH-PPV interface is significantly reduced, leading to an improvement in hole injection.The interface state density (Nss) values and the time constant of the interface states (τ) are obtained by the development of a new approach by the fit of the capacitance with three capacitances in series, according to Nicollian and Goetzberger formula. A decrease in the interface state density is observed when the Au interlayer is introduced at the ITO/organic layer interface. The main factors contributing to such improvements induced by the thin gold buffer layer are discussed.

표면분석 장비를 활용한 차세대 나노소자 물성분석

Jouhahn Lee The new materials such as graphene and other nano scale structured materials are attracting great attention due to its expandability for the future electronic devices. In this presentation, a variety of analysis techniques will be introduced for the latest new material applications such as graphene and organic materials with number of metals. The basic properties of next generation device should be carefully analyzed without being exposed to ambient surrounding since the physical and chemical properties of new material or interface states are easily and drastically changed by ambient condition. With the combination of the fabrication process and precise analysis instruments, it is expected to set the facilities supporting the nanotechnology industry and other research groups. This system will give strong support nanotechnology and other complex science with qualified data and information on basic knowledge on the new-forthcoming materials for the future.

Evaluation of interface state density of strained-Si metal-oxide-semiconductor interfaces by conductance method

In this study, the application of the conductance method to bi-axially strained-Si (sSi) MOS capacitors on relaxed SiGe buffer layers is examined for evaluating the properties of sSi MOS interface states. It is found that the conventional conductance method does not work well for the characterization of SiO2/sSi MOS interfaces, because of additional parasitic admittance related to the sSi/SiGe hetero-interface. This additional parasitic admittance cannot be eliminated by the series resistance correction (SRC). A new equivalent circuit model for the SiO2/sSi interfaces, utilized in the conductance analysis, is proposed. The proposed model takes the sSi/SiGe hetero-interface parasitic admittance into account. By employing this new model and the analysis by a device simulator, physical parameters of the SiO2/sSi MOS interface states, generated by Fowler-Nordheim stress, are extracted. It is found that the introduced biaxial tensile strain does not strongly change the properties of SiO2/Si interface states.

Frequency dependent interface state properties of a Schottky device based on perylene-monoimide deposited on n-type silicon by spin coating technique

We have reported a detailed investigation of frequency dependent properties of the Au/perylene-monoimide (PMI)/n-Si Schottky diodes in this study. Schottky diodes based on PMI have been fabricated by spin coating method. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics have been measured in the frequency range from 30kHz to 1MHz at room temperature. The values of measured capacitance Cm and conductance Gm under both reverse and forward bias have been corrected for the effect of series resistance to obtain the real diode capacitance and the conductance values. The density of interface states (Dit) distribution profiles as a function of frequency has been extracted from the corrected C–V and G–V measurements. Interface trap states of the PMI/n-Si Schottky device have decreased by increasing the applied frequency and were found to be 8.13×1011 and 1.75×1011eV−1cm−2 for 30kHz and 1MHz, respectively.

Electrical Properties and Interface States of Rare-Earth Metal Ytterbium Schottky Contacts to p-Type InP

The electronic parameters and interface state properties of Yb/p-InP Schottky diode have been investigated by current­voltage (I­V), capacitance­voltage­frequency (C­V­f) and conductance­voltage­frequency (G­V­f) measurements at room temperature. The barrier height and ideality factor of the Yb/p-InP Schottky diode are found to be 0.68eV (I­V)/0.79eV (C­V) and 1.24, respectively. As well, the values of barrier heights, ideality factors and series resistance are estimated by Cheung and Norde methods are compared. Under forward bias conditions, ohmic and space charge limited conduction (SCLC) mechanisms are identified at low and higher voltages, respectively. The C­V characteristics of the Yb/p-InP Schottky diode are also measured at different frequencies at room temperature. Further, the C­f and G­f measurements of the