Tunable topological interface states and resonance states of surface waves based on the shape memory alloy

Topological interface state(TIS)of elastic wave has attracted significant research interest due to its potential prospects in strengthening acoustic energy and enhancing the signal accuracy of damage identification and quantification.However,previous implementations on the interface modes of surface waves are limited to the non-adjustable frequency band and unalterable mode width.Here,we demonstrate the tunable TIS and topological resonance state(TRS)of Rayleigh wave by using a shape memory alloy(SMA)stubbed semi-infinite one-dimensional(1D)solid phononic crystals(PnCs),which simultaneously possesses the adjustable mode width.The mechanism of tunability stems from the phase transformation of the SMA between the martensite at low temperature and the austenite at high temperature.The tunable TIS of Rayleigh wave is realized by combining two bandgap-opened PnCs with different Zak phases.The TRS with adjustable mode width is achieved in the heterostructures by adding PnCs with Dirac point to the middle of two bandgap-opened PnCs with different Zak phases,which exhibits the extraordinary robustness in contrast to the ordinary Fabry–Perot resonance state.This research provides new possibilities for the highly adjustable Rayleigh wave manipulation and find promising applications such as tunable energy harvesters,wide-mode filters,and high-sensitivity Rayleigh wave detectors.

Incomplete charge transfer in CMOS image sensor caused by Si/SiO_(2)interface states in the TG channel

CMOS image sensors produced by the existing CMOS manufacturing process usually have difficulty achieving complete charge transfer owing to the introduction of potential barriers or Si/SiO_(2)interface state traps in the charge transfer path,which reduces the charge transfer efficiency and image quality.Until now,scholars have only considered mechanisms that limit charge transfer from the perspectives of potential barriers and spill back effect under high illumination condition.However,the existing models have thus far ignored the charge transfer limitation due to Si/SiO_(2)interface state traps in the transfer gate channel,particularly under low illumination.Therefore,this paper proposes,for the first time,an analytical model for quantifying the incomplete charge transfer caused by Si/SiO_(2)interface state traps in the transfer gate channel under low illumination.This model can predict the variation rules of the number of untransferred charges and charge transfer efficiency when the trap energy level follows Gaussian distribution,exponential distribution and measured distribution.The model was verified with technology computer-aided design simulations,and the results showed that the simulation results exhibit the consistency with the proposed model.

Two-dimensional analysis of the interface state effect on current gain for a 4H-SiC bipolar junction transistor

This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H-SiC bipolar junction transistor （BJT）. Simulation results indicate the mechanism of current gain degradation, which is surface Fermi level pinning leading to a strong downward bending of the energy bands to form the channel of surface electron recombination current. The experimental results are well-matched with the simulation, which is modeled by exponential distributions of the interface state density replacing the single interface state trap. Furthermore, the simulation reveals that the oxide quality of the base emitter junction interface is very important for 4H-SiC BJT performance.

Characterization of Interface State Density of Ni/p-GaN Structures by Capacitance/Conductance-Voltage-Frequency Measurements

For the frequency range of I kHz-lOMHz, the interface state density of Ni contacts on p-GaN is studied using capacitance-voltage （C-V） and conductance-frequency-voltage （G-f-V） measurements at room temperature. To obtain the real capacitance and interface state density of the Ni/p-GaN structures, the effects of the series resistance （Rs） on high-frequency （SMHz） capacitance values measured at a reverse and a forward bias are investigated. The mean interface state densities obtained from the CHF-CLF capacitance and the conductance method are 2 ×1012 e V-1 cm-2 and 0.94 × 1012 eV-1 cm-2, respectively. Furthermore, the interface state density derived from the conductance method is higher than that reported from the Ni/n-GaN in the literature, which is ascribed to a poor crystal quality and to a large defect density of the Mg-doped p-GaN.

Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I-V （current-voltage） characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.

Interface states study of intrinsic amorphous silicon for crystalline silicon surface passivation in HIT solar cell

Intrinsic hydrogenated amorphous silicon（a-Si：H） film is deposited on n-type crystalline silicon（c-Si） wafer by hotwire chemical vapor deposition（HWCVD） to analyze the amorphous/crystalline heterointerface passivation properties.The minority carrier lifetime of symmetric heterostructure is measured by using Sinton Consulting WCT-120 lifetime tester system,and a simple method of determining the interface state density（D_（it）） from lifetime measurement is proposed.The interface state density（D_（it）） measurement is also performed by using deep-level transient spectroscopy（DLTS） to prove the validity of the simple method.The microstructures and hydrogen bonding configurations of a-Si：H films with different hydrogen dilutions are investigated by using spectroscopic ellipsometry（SE） and Fourier transform infrared spectroscopy（FTIR） respectively.Lower values of interface state density（D_（it）） are obtained by using a-Si：H film with more uniform,compact microstructures and fewer bulk defects on crystalline silicon deposited by HWCVD.

Low voltage substrate current： a monitor for interface states generation in ultra-thin oxide n-MOSFETs under constant voltage stresses

The low voltage substrate current （Ib） has been studied based on generation kinetics and used as a monitor of interface states （Nit） generation for ultra-thin oxide n-MOSFETs under constant voltage stress. It is found that the low voltage Ib is formed by electrons tunnelling through interface states, and the variations of Ib（△Ib） are proportional to variations of Nit （△Nit）. The Nit energy distributions were determined by differentiating Nit（Vg）. The results have been compared with that measured by using gate diode technique.

Influence of interface states, conduction band offset, and front contact on the performance of a-SiC：H(n)/c-Si(p)heterojunction solar cells

P-type silicon heterojunction（SHJ） solar cells with a-SiC：H（n） emitters were studied by numerical computer simulation in this paper. The influence of interface states, conduction band offset, and front contact on the performance of a-SiC：H（n）/c-Si（p） SHJ solar cells was investigated systematically. It is shown that the open circuit voltage（Voc） and fill factor（F F） are very sensitive to these parameters. In addition, by analyzing equilibrium energy band diagram and electric field distribution, the influence mechanisms that interface states, conduction band offset, and front contact impact on the carrier transport, interface recombination and cell performance were studied in detail. Finally, the optimum parameters for the a-SiC：H（n）/c-Si（p） SHJ solar cells were provided. By employing these optimum parameters, the efficiency of SHJ solar cell based on p-type c-Si was significantly improved.

Fermi level pinning effects at gate–dielectric interfaces influenced by interface state densities

The dependences of Fermi-level pinning on interface state densities for the metal-dielectric, ploycrystalline silicon-dielectric, and metal silicide-dielectric interfaces are investigated by calculating their effective work functions and their pinning factors. The Fermi-level pinning factors and effective work functions of the metal-dielectric interface are observed to be more susceptible to the increasing interface state densities, differing significantly from that of the ploycrystalline silicon-dielectric interface and the metal silicide-dielectric interface. The calculation results indicate that metal silicide gates with high-temperature resistance and low resistivity are a more promising choice for the design of gate materials in metal-oxide semiconductor（MOS） technology.

Experimental evaluation of interface states during time-dependent dielectric breakdown of GaN-based MIS-HEMTs with LPCVD-SiNχgate dielectric

We experimentally evaluated the interface state density of GaN MIS-HEMTs during time-dependent dielectric breakdown(TDDB).Under a high forward gate bias stress,newly increased traps generate both at the SiNx/AlGaN interface and the SiNx bulk,resulting in the voltage shift and the increase of the voltage hysteresis.When prolonging the stress duration,the defects density generated in the SiNx dielectric becomes dominating,which drastically increases the gate leakage current and causes the catastrophic failure.After recovery by UV light illumination,the negative shift in threshold voltage(compared with the fresh one)confirms the accumulation of positive charge at the SiNx/AlGaN interface and/or in SiNx bulk,which is possibly ascribed to the broken bonds after long-term stress.These results experimentally confirm the role of defects in the TDDB of GaN-based MIS-HEMTs.

Determination of interface states and their time constant for Au/SnO_2 /n-Si (MOS) capacitors using admittance measurements

The frequency dependence of admittance measurements （capacitance–voltage （C–V ） and conductance–voltage （G/ω–V ）） of Au/SnO2 /n-Si （MOS） capacitors was investigated by taking into account the effects of the interface states （N ss ） and series resistance （Rs ） at room temperature. Admittance measurements were carried out in frequency and bias voltage ranges of 1 kHz–1 MHz and （ 5V）–（＋9V）, respectively. The values of N ss and R s were determined by using a conductance method and estimating from the admittance measurements of the MOS capacitors. At low frequencies, the interface states can follow the AC signal and yield excess capacitance and conductance. In addition, the parallel conductance （G p /ω） versus log（f） curves at various voltages include a peak due to the presence of interface states. It is observed that the N ss and their time constant （τ） range from 1.23 ×10 12 eV-1 ·cm-2 to 1.47 ×10 12 eV-1 ·cm-2 and from 7.29 ×10-5 s to 1.81 ×10-5s, respectively.

Bias-induced reconstruction of hybrid interface states in magnetic molecular junctions

Based on first-principles calculations,the bias-induced evolutions of hybrid interface states inπ-conjugated tricene and in insulating octane magnetic molecular junctions are investigated.Obvious bias-induced splitting and energy shift of the spin-resolved hybrid interface states are observed in the two junctions.The recombination of the shifted hybrid interface states from different interfaces makes the spin polarization around the Fermi energy strongly bias-dependent.The transport calculations demonstrate that in theπ-conjugated tricene junction,the bias-dependent hybrid interface states work efficiently for large current,current spin polarization,and distinct tunneling magnetoresistance.But in the insulating octane junction,the spin-dependent transport via the hybrid interface states is inhibited,which is only slightly disturbed by the bias.This work reveals the phenomenon of bias-induced reconstruction of hybrid interface states in molecular spinterface devices,and the underlying role of conjugated molecular orbitals in the transport ability of hybrid interface states.

Dual-channel tunable near-infrared absorption enhancement with graphene induced by coupled modes of topological interface states

The dual-channel nearly perfect absorption is realized by the coupled modes of topological interface states(TIS) in the near-infrared range. An all-dielectric layered heterostructure composed of photonic crystals(Ph C)/graphene/Ph C/graphene/Ph C on Ga As substrate is proposed to excite the TIS at the interface of adjacent Ph C with opposite topological properties. Based on finite element method(FEM) and transfer matrix method(TMM), the dualchannel absorption can be modulated by the periodic number of middle Ph C, Fermi level of graphene, and angle of incident light(TE and TM polarizations). Especially, by fine-tuning the Fermi level of graphene around 0.4 e V, the absorption of both channels can be switched rapidly and synchronously. This design is hopefully integrated into silicon-based chips to control light.

Interface states in Al_2O_3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique

Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/A1GaN/GaN metal-oxide-semiconductor （MOS） structures. Two types of device structures, namely, the recessed gate structure （RGS） and the normal gate structure （NGS）, are studied in the experiment. Interface trap parameters includ-ing trap density Dit, trap time constant ιit, and trap state energy ET in both devices have been determined. Furthermore, the obtained results demonstrate that the gate recess process can induce extra traps with shallower energy levels at the Al2O3/AlGaN interface due to the damage on the surface of the AlGaN barrier layer resulting from reactive ion etching （RIE）.

Power loss transition of stable ZnO varistor ceramics: Role of oxygen adsorption on the stability of interface states at the grain boundary

Highly stable ZnO varistor ceramics with steadily decreasing power loss have been put into applications in electrical and electronic systems for overvoltage protections, even with the absence of general understandings on their aging behaviors. In this paper, we investigated their aging nature via conducting comparative direct current (DC) aging experiments both in air and in nitrogen, during which variations of electrical properties and interface properties were measured and analyzed. Notably, continuously increasing power loss with severe electrical degradation was observed for the sample aged in nitrogen. The power loss transition was discovered to be closely related to the consumption of oxygen adsorption at the grain boundary (GB), which could, however, remain constant for the sample aged in air. The interface density of states (DOS) Ni, which is crucial for pinning the potential barrier, was proved to decrease in nitrogen, but keep stable in air. Therefore, it is concluded that the oxygen adsorption at the GB is significant for the stability of interface states, which further correlates to the long-term stability of modern stable ZnO varistor ceramics.

Photonic and phononic interface states based on sunflower-type crystals[Invited]

Interface states are widely applied in waveguide devices.However,previous studies failed to achieve photonic and phononic interface states independent of each other in the same crystal structure depending on the behavior of the crystal structure,i.e.,photonic or phononic crystals,making the function of interface states single.In this study,straight-line and circular photonic and phononic interface states were realized independently in sunflower-type crystals.In addition,with a defect and a metal barrier,interface states could remain almost undamaged.The results have the potential to achieve multifunction devices and reduce the cost of engineering applications.

Stimulated photoluminescence emission and trap states in Si/SiO_2 interface formed by irradiation of laser

Stimulated photoluminescence （PL） emission has been observed from an oxide structure of silicon when optically excited by a radiation of 514nm laser. Sharp twin peaks at 694 and 692nm are dominated by stimulated emission, which can be demonstrated by its threshold behaviour and linear transition of emission intensity as a function of pump power. The oxide structure is formed by laser irradiation on silicon and its annealing treatment. A model for explaining the stimulated emission is proposed, in which the trap states of the interface between an oxide of silicon and porous nanocrystal play an important role.

Extraction of interface state density and resistivity of suspended p-type silicon nanobridges

The evaluation of the influence of the bending deformation of silicon nanobridges on their electrical properties is crucial for sensing and actuating applications. A combined theory/experimental approach for de- termining the resistivity and the density of interface states of the bending silicon nanobridges is presented. The suspended p-type silicon nanobridge test structures were fabricated from silicon-on-insulator wafers by using a standard CMOS lithography and anisotropic wet etching release process. After that, we measured the resistance of a set of silicon nanobridges versus their length and width under different bias voltages. In conjunction with a theoretical model, we have finally extracted both the interface state density of and resistivity suspended silicon nanobridges under different bending deformations, and found that the resistivity of silicon nanobridges without bending was 9.45 mΩ.cm and the corresponding interface charge density was around 1.7445 × 10^13 cm-2. The bending deformation due to the bias voltage slightly changed the resistivity of the silicon nanobridge, however, it significantly changed the distribution of interface state charges, which strongly depends on the intensity of the stress induced by bending deformation.

Significantly enhanced varistor properties of CaCu_(3)Ti_(4)O_(12) based ceramics by designing superior grain boundary:Deepening and broadening interface states

Significantly enhanced varistor properties via tailoring interface states were obtained in Ca_(1-2x/3)Y_(x)Cu_(3)Ti_(4)O_(12)-SrCu_(3)Ti_(4)O_(12) composite ceramics.The breakdown field was improved to 35.8 kV cm^(-1) and the nonlinear coefficient in 0.1-1 mA cm^(-2) was enhanced to 14.6 for Ca_(0.67)Y_(0.5)Cu_(3)Ti_(4)O_(12)-SrCu_(3)Ti_(4)O_(12).Noticeably,the withstand voltage of single grain boundary reached up to 24 V while the reported ones were constant to about 3 V.Greatly improved properties were attributed to the formation of superior grain boundary rather than the reduced grain size.Surprisingly,with distinct discrepancy of nonlinear performance in the composites,the resistance and activation energy of grain boundary exhibited little differences.Based on the double Schottky barrier at grain boundary and the field-assisted thermal emission model,it was found that the excellent electrical nonlinearity arose from the formation of deeper and broader interface states at grain boundary.In this case,interface states were not easily entirely filled and the barrier could maintain its height under applied voltage.This work provides a novel routine for enhancing the varistor properties of CaCu_(3)Ti_(4)O_(12) based ceramics by manipulating interface states at grain boundary.

Tailoring edge and interface states in topological metastructures exhibiting the acoustic valley Hall effect

In this study, we investigate the acoustic topological insulator or topological metastructure, where an acoustic wave can exist only in an edge or interface state instead of propagating in bulk. Breaking the structural symmetry enables the opening of the Dirac cone in the band structure and the generation of a new band gap, wherein a topological edge or interface state emerges.Further, we systematically analyze two types of topological states that stem from the acoustic valley Hall effect mechanism;one type is confined to the boundary, whereas the other type can be observed at the interface between two topologically different structures. Results denote that the selection of different boundaries along with appropriately designed interfaces provides the acoustic waves in the band gap range with abilities of one-way propagation, dual-channel propagation, immunity from backscattering at sharp corners, and/or transition between propagation at interfaces and boundaries. Furthermore, we show that the acoustic wave propagation paths can be tailored in diverse and arbitrary ways by combing the two aforementioned types of topological states.