Types Of Interface States Research Articles

Zak phase induced multiband waveguide by two-dimensional photonic crystals.

Interface states in photonic crystals provide efficient approaches to control the flow of light. Photonic Zak phase determines the bulk band properties of photonic crystals, and, by assembling two photonic crystals with different bulk band properties together, deterministic interface states can be realized. By translating each unit cell of a photonic crystal by half the lattice constant, another photonic crystal with identical common gaps but a different Zak phase at each photonic band can be created. By assembling these two photonic crystals together, multiband waveguide can thus be easily created and then experimentally characterized. Our experimental results have good agreement with numerical simulations, and the propagation properties of these measured interface states indicate that this new type of interface state will be a good candidate for future applications of optical communications.

Experimental Characterization of the Deterministic Interface States in Two-Dimensional Photonic Crystals

The study of interface/surface states in photonic crystals provides new approaches to control the flow of light. In this work, a new type of interface states in two-dimensional photonic crystals is experimentally realized and characterized [1]. The existence of this type of interface states is solely dependent on the reflection properties of the bulk photonic crystals without any surface/interface decorations. Our experimental results have excellent agreement to numerical simulations and the propagation properties of these measured interface states indicate that this new type of interface states will be a good candidate for future optical waveguiding applications. This type of deterministic interface states also exists at the boundary between a dielectric photonic crystal and its “inverted” partner as long as a common gap can be found above the lowest band, which is also experimentally characterized [2].

Interface traps density-of-states as a vital component for hot-carrier degradation modeling

We refine our approach for hot-carrier degradation modeling based on a thorough evaluation of the carrier energy distribution by means of a full-band Monte–Carlo simulator. The model is extended to describe the linear current degradation over a wide range of operation conditions. For this purpose we employ two types of interface states, either created by single- or by multiple-electron processes. These traps apparently have different densities of states which is important to consider when calculating the charges stored in these traps. By calibrating the model to represent the degradation of the transfer characteristics, we extract the number of particles trapped by both types of interface traps. We find that traps created by the single- and multiple-electron mechanisms are differently distributed over energy with the latter shifted toward higher energies. This concept allows for an accurate representation of the degradation of the transistor transfer characteristics.

Effect of dopant (Nb) concentration on the grain boundary electrical properties of Nb-doped barium titanate

A series of coarse-grained BaTiO3 specimens with different dopant (Nb) concentrations were prepared by adjusting the oxygen partial pressure during sintering. They were again heat-treated in air, and the behavior of the grain boundary electrical properties with the increase of Nb concentration was investigated under the conditions of the same microstructure and heat treatment. The interface states of the grain boundaries were estimated using the grain boundary R (resistance) and C (capacitance) values at each temperature that were obtained from impedance analysis. An increase in the interface state density at certain energy levels with increasing Nb concentration was verified experimentally. One type of interface state was observed for specimens with low Nb concentrations and another for specimens with high Nb concentrations. It is proposed that the changes in the interface state with increasing Nb concentration are related to the transition of the compensating defect mode and differences in the extent of oxygen adsorption at the grain boundaries.

Interface states induced by the presence of trapped holes near the silicon–silicon-dioxide interface

Trapped holes are shown to induce ‘‘slow’’ interface states by their presence that are distinctly different from other types of interface states. These slow states can be alternately introduced and removed by sequential hole generation and annihilation. Various experiments and techniques are used to rule out explanations involving artifacts due to lateral nonuniformities in the hole trapping.

Generation and anneal of a new kind of interface state in stressed and high-temperature annealed metal-oxide-semiconductor devices

Polycrystalline silicon (poly) gate metal-oxide-semiconductor (MOS) transistors were electrically stressed by constant-current tunneling. After the stress the devices were thermally annealed for variable times in the temperature range between 800 and 950 °C, and a second tunneling stress was performed. Capacitance-voltage (C-V) curve broadening and a charge pumping (CP) technique were used to detect interface state generation. It was found that the stress generated interface states are totally annealed by the thermal treatment. On the other hand, generation rates and saturation values, due to the second stress after annealing, exceed those of the fresh devices. Analysis of the generation process indicates that two types of interface states are generated: one, similar in its generation rate and saturation value to that of a fresh device, and another one, which is characterized by a higher generation rate and saturation value, is attributed to a new type of latent site. The density of this new type of latent interface states site decays exponentially with the annealing time. The annealing rate follows a temperature-dependent Arrhenius function. The anneal of this new type of interface state is characterized by an activation energy of 3.47 eV.

Investigation of interface states and fermi level pinning mechanisms with metals on InP(110) surfaces

Metal/InP(110) interfaces have been systematically studied using photoelectron Spectroscopy. This work aims at understanding the physical nature of interface states and Fermi level pinning mechanisms. Clear-cut experimental evidence shows that two types of interface states are responsible for Fermi level pinning. At the disrupted interfaces which occur at room temperature, a large amount of defects are generated during various interfacial processes and pin the surface Fermi levels around 0.95 eV above the valence band maximum (VBM). On the contrary, much fewer defects are present at the nearly perfect interfaces which are obtainable at reduced temperature. In these cases, the metal induced gap states play an overwhelming role, and the Fermi level is pinned around 0.75 eV above the VBM. It is also concluded that interplay between the two mechanisms should be taken into account in order to understand the process of Schottky barrier formation.

Interface state generation mechanism in n-MOSFET's

Uniform carrier injection into the channel of n-MOSFETs generates two types of interface states, depending on the oxide electric field: One is linearly proportional to the injected electron density (Type I), while the other shows a half-power dependence (Type II). Charge-pumping measurements in the temperature range of 77K and 263K show that the type I interface states are located in the mid-gap, while the type II interface states are uniformly distributed in wide energy range. Holes generated at the gate/SiO 2 interface or in the oxide are found to be responsible for the type I interface states, while hydrogen or hydrogen compounds diffusing from the interface cause the type II interface states.

The temperature dependence of the photoconductivity in a-Si:H/a-SiNx:H superlattices

The temperature dependence of the photoconductivity σp(T) in a-Si:H/a-SiNx:H superlattices does not decrease with temperature decreasing in the range of 120-250K, but it is temperature independent showing a wide plateau of photoconductivity σp in the superlattices with thickness of a-Si:H layer dSi = 12 and 57nm. The plateau of σp(T) depends on the light intensity. One type of interface state as sensitizing centre was proposed. The parameters of the sensitizing centre were determined by using computer fitting of σp(T). The computed results are the same with the experimental data.

Electro‐optical Investigation of the Potential Drop at III/V Semiconductor/Electrolyte Interfaces

The semiconductor/electrolyte junction is investigated for n‐type , , and in contact with aqueous and nonaqueous electrolytes. Electrolyte electroreflectance is used as an in situ probe for determining the distribution of potential and energy states at the interface. We find that interface states at and electrodes have a density of and , respectively, and that this density is pH independent for (semiconductor controlled), whereas for it is pH dependent (solvent controlled). For , the situation is more complex, and interfaces clean from energy states (density lower than 1012 cm−2 eV−1) can be obtained at pH 0 as well as a complete Fermi level pinning (density ∼1015 cm−2 eV−1) depending on the bias. At pH 14 and in propylene carbonate, the interface states density is large and bias independent. Therefore, we conclude that two types of interface states may exist, electrochemical (pH 0) and chemical (pH 14), and the former cannot be removed electrochemically.

Theory of Capacitance‐Voltage Characteristics of Semiconductor Electrodes with Interface States

Theory of characterization method for semiconductor electrodes with interface states has been developed under the assumption that the interface states are in quasi‐equilibrium with the electrolyte. Model calculation based on this theory has well reproduced the observed C‐V characteristics in electrodes. It is pointed out that dispersive Mott‐Schottky plots give a variety of information about energetics of a semiconductor‐electrolyte contact. The surface structure of the electrode has been clarified in some detail. Some electrodes may have two types of interface states. The distribution of the shallower one can be expressed by a gaussian with a standard deviation of ∼800Å, and the deeper one by an exponential function with deep penetrating length. The interface state seems to be the reason why electrodes have a large quantum efficiency.

Use of the Subthreshold Behavior to Compare X-Ray and CO-60 Radiation-Induced Defects in MOS Transistors

Transistor behavior in the subthreshold region is used to compare the production of oxide trapped charge and interface states produced by x-ray and Co-60 radiation. For the oxides used in this study, the subthreshold data indicates the presence of two types of interface states. One of these interface states appears to differ from the more commonly observed amphoteric defect. The characteristics of these states suggest that they are donor defects. These states further complicate testing protocols because they anneal at room temperature. A modification to the subthreshold measurement technique of McWhorter and Winokur is proposed for oxides in which these donor states occur. Using this revised subthreshold technique, less interface dose enhancement occurs during x-ray exposures than was observed previously with thick-oxide-capacitor measurements.

On occupation functions of donor- and acceptor-like interface states in metal-insulator-semiconductor tunnel structures

This paper presents a theoretical study on the occupation functions of interface states in MIS tunnel structures. Based on Shockley-Read-Hall (SRH) statistics and considering carriers tunneling between the metal and interface states, occupation functions of both donor- and acceptor-like interface states at arbitrary energy level within the semiconductor band gap are derived and analyzed. It reveals that, for the same energy level, the occupation functions of donor-like and acceptor-like interface states are remarkably different in magnitude. The deviation in occupation functions of these two types of interface states is a nonlinear function of the ratio of capture cross-section of the charge states to that of the neutral states ( C C/ C N) and the semiconductor surface conditions. If the insulating layer (SiO 2) is relatively thick (> 50 Å) or thin (< 10 Å), interface states are in equilibrium with the semiconductor or the metal, respectively. Under the circumstances, the occupation functions of the two types of interface states are no longer distinguishable. Alternatively, they can be approximated by the well-known Fermi-Dirac distribution function. In this paper, quantitative influences of key parameters of MIS tunnel structures such as insulating layer thickness, electron and hole density at the semiconductor surface, capture cross-sections for charged and neutral states, etc., on interface states occupation function are discussed. For Gaussian-distributed donor- and acceptor-like interface states, the quantitative roles of interface states in charge storage and current-assisting effects are also demonstrated.

Interface states at the SiO 2-Si interface

The present understanding of interface states at the SiO 2-Si interface is reviewed. Typical results of measurement techniques are presented and critically discussed with respect to identification of types and origins of interface states. Only one type of interface state is observed after strong hydrogen annealing. The density of these interface states decays from D it ≧ 10 10 cm −2 eV −1 near the conduction band to extremely low values of D it ≦ 10 8 cm −2 eV −1 in the lower half of the Si band gap. A peak of interface states is observed below midgap. The density of bulk traps in silicon is comparable to the low interface state density. Among the various models of interface states proposed, the trivalent silicon dangling bond, bond angle distortions, and discrete traps in the interfacial layer are possible explanations of the various types of interface states.

Optically active interface states in MOS structures

The results of studies of the interface states in clean n-type MOS capacitors by the low-temperature photocapacitance technique are reported. Energy distribution of the interface states density and photoionization cross-section are determined from the analysis of the photocapacitance kinetic. It is shown that the energy distribution of the interface state density can be described by the Gaussian distribution with maximum at about 0.7 eV below the conduction band edge and standard deviation of about 0.1 eV. The photoionization cross-section of these states can be described by the Lucovsky relationship. The maximum of the photoionization cross-section vs photon energy was equal to about 5 × 10 −20/( E c − E ss ) cm 2 for a given energy of the interface states E ss . From the comparison of the photocapacitance and quasi-static C-V measurements the existence of two types of interface states is suggested: “optically active states” with density decreasing towards the band edges, and “optically inactive states” with density increasing towards the band edges. No photocapacitance associated with “optically inactive states” was observed.

Self-consistent calculations of interface states and electronic structure of the (110) interfaces of Ge-GaAs and AlAs-GaAs

Self-consistent pseudopotential techniques, together with a superlattice geometry, are used to investigate the detailed electronic structure of the (110) interfaces of Ge-GaAs and AlAs-GaAs. For Ge-GaAs six types of interface states are found, all lying below the thermal gap. No interface states are found in AlAs-GaAs. For each interface the total charge density, self-consistent potential, projected band structure, and local density of states are presented. The interface states in Ge-GaAs are discussed in detail. We also present results for the conduction- and valence-band discontinuities at these interfaces, discuss superlattice states in AlAs-GaAs, and suggest possible relaxation at the Ge-GaAs (110) interface.

Ge-GaAs (110) Interface: A Self-Consistent Calculation of Interface States and Electronic Structure

Self-consistent calculations allowing electron redistribution in a wide region around a Ge-GaAs(110) interface reveal six types of interface states. The charge densities and local density of states at the interface indicate Ge-Ga bonding states in the gap (but below the valence-band maximum) and a variety of other states at lower energy. Some estimates based on these pseudopotential results give information on band-edge discontinuities and the character of bonds across a nonpolar interface.