Microstructural Models of Alumina Nanotubes and Anodic Porous Alumina Film Formed in Sulphuric Acid

Electrochemical stepwise anodization of aluminium in dilute sulphuric acid results in the formation of alumina nanotubes (ANTs) due to the hexagonal split of the anodic porous alumina (APA) film along the cell boundaries containing many voids;that is,the ANTs are the completely detached cell of the APA film.The inner diameters of the ANTs are in the range of 10-20nm,and the aspect ratio (inner diameter/length) of the ANTs can be about 80.The relations found for pore diameter,cell diameter and barrier layer thickness are around 1,2.7 and 0.85 nm/V,respectively.Transmission electron microscopy (TEM) reveals that the ANT wall has a three-shell structure:an outer shell (metal/oxide interface) consisting of pure alumina oxide,a middle shell of the hydrated oxide or/and hydroxide and an inner shell (oxide/electrolyte interface) of anion incorporated oxide with the thickness ratio of 1:1:2.The structural change of ANTs induced by e-beam irradiation in TEM indicates that the thermal instability of the hydrated oxide or/and hydroxide within the cell wall might be an alternative origin contributing to the self-organization of the cells,leading to a densely packed triangular cell lattice of the APA film.     

Thermodynamic criterion for searching high mobility two-dimensional electron gas at KTaO_3 interface

Two-dimensional electron gases(2 DEGs) formed at the interface between two oxide insulators present a promising platform for the exploration of emergent phenomena.While most of the previous works focused on SrTiO_(3-)based 2 DEGs,here we took the amorphous-ABO_3/KTaO_3 system as the research object to study the relationship between the interface conductivity and the redox property of B-site metal in the amorphous film.The criterion of oxide-oxide interface redox reactions for the B-site metals,Zr,Al,Ti,Ta,and Nb in conductive interfaces was revealed:the formation heat of metal oxide,ⅢH_f~o,is lower than-350 kJ/(mol O) and the work function of the metal Φ is in the range of 3.75 eVΦ 4.4 eV.Furthermore,we found that the smaller absolute value of ⅢH_f~o and the larger value of Φ of the B-site metal would result in higher mobility of the two-dimensional electron gas that formed at the corresponding amorphous-ABO_3/KTaO_3 interface.This finding paves the way for the design of high-mobility all-oxide electronic devices.     

Charge trapping behavior and its origin in Al_2O_3/SiC MIS system

Charge trapping behavior and its origin in Al2O3/SiC MOS structure are investigated by analyzing the capacitance–voltage(C–V) hysteresis and the chemical composition of the interface. The C–V hysteresis is measured as a function of oxide thickness series for an Al2O3/SiC MIS capacitor. The distribution of the trapped charges, extracted from the C–V curves, is found to mainly follow a sheet charge model rather than a bulk charge model. Therefore, the electron injection phenomenon is evaluated by using linear fitting. It is found that most of the trapped charges are not distributed exactly at the interface but are located in the bulk of the Al2O3 layers, especially close to the border. Furthermore, there is no detectable oxide interface layer in the x-ray photoelectron spectroscope(XPS) and transmission electron microscope(TEM)measurements. In addition, Rutherford back scattering(RBS) analysis shows that the width of the Al2O3/SiC interface is less than 1 nm. It could be concluded that the charge trapping sites in Al2O3/SiC structure might mainly originate from the border traps in Al2O3 film rather than the interface traps in the interfacial transition layer.     

Evolution of the structural and optical properties of silver oxide films with different stoichiometries deposited by direct-current magnetron reactive sputtering

Nitrogen doping of silver oxide(AgxO) film is necessary for its application in transparent conductive film and diodes because intrinsic AgxO film is a p-type semiconductor with poor conductivity.In this work,a series of AgxO films is deposited on glass substrates by direct-current magnetron reactive sputtering at different flow ratios(FRs) of nitrogen to O2.Evolutions of the structure,the reflectivity,and the transmissivity of the film are studied by X-ray diffractometry and sphectrophotometry,respectively.The specular transmissivity and the specular reflectivity of the film decreasing with FR increasing can be attributed to the evolution of the phase structure of the film.The nitrogen does not play the role of an acceptor dopant in the film deposition.     

Variation of passivation behavior induced by sputtered energetic particles and thermal annealing for ITO/SiO_x/Si system

The damage on the atomic bonding and electronic state in a SiO_x(1.4-2.3 nm)/c-Si(150 μm) interface has been investigated.This occurred in the process of depositing indium tin oxide(ITO) film onto the silicon substrate by magnetron sputtering.We observe that this damage is caused by energetic particles produced in the plasma(atoms,ions,and UV light).The passivation quality and the variation on interface states of the SiO_x/c-Si system were mainly studied by using effective minority carrier lifetime(τ_(eff)) measurement as a potential evaluation.The results showed that the samples' τ_(eff)was reduced by more than 90%after ITO formation,declined from 107 μs to 5 μs.Following vacuum annealing at 200 ℃,the τ_(eff) can be restored to 30 μs.The components of Si to O bonding states at the SiO_x/c-Si interface were analyzed by x-ray photoelectron spectroscopy(XPS) coupled with depth profiling.The amorphous phase of the SiO_x layer and the "atomistic interleaving structure" at the SiO_x/c-Si interface was observed by a transmission electron microscope(TEM).The chemical configuration of the Si-O fraction within the intermediate region is the main reason for inducing the variation of Si dangling bonds(or interface states) and effective minority carrier lifetime.After an appropriate annealing,the reduction of the Si dangling bonds between SiO_x and near the c-Si surface is helpful to improve the passivation effect.     

A Novel Contactless Method for Characterization of Semiconductors：Surface Electron Bean Induced Voltage in Scanning Electron Microscopy

We present a novel contactless and nondestructive method called the surface electron beam induced voltage (SEBIV) method for characterizing semiconductor materials and devices.The SEBIV method is based on the detection of the surface potential induced by electron beams of scanning electron microscopy (SEM).The core part of the SEBIV detection set-up is a circular metal detector placed above the sample surface.The capacitance between the circular detector and whole surface of the sample is estimated to be about 0.64pf.It is large enough for the detection of the induced surface potential.The irradiation mode of electron beam (e-beam) influences the signal generation When the e-beam irradiates on the surface of semiconductors continuously,a differential signal is obtained.The real distribution of surface potentials can be obtained when a pulsed e-beam with a fixed frequency is used for irradiation and a lock-in amplifier is employed for detection.The polarity of induced potential depends on the structure of potential barriers and surface states of samples.The contrast of SEBIV images in SEM changes with irradiation time and e-beam intensity.     

Built-in electric field effect on cyclotron mass of magnetopolarons in a wurtzite In_xGa_（1-x）N/GaN quantum well

The cyclotron mass of magnetopolarons in wurtzite In x Ga 1 x N/GaN quantum well is studied in the presence of an external magnetic field by using the Larsen perturbation method.The effects of the built-in electric field and different phonon modes including interface,confined and half-space phonon modes are considered in our calculation.The results for a zinc-blende quantum well are also given for comparison.It is found that the main contribution to the transition energy comes from half-space and interface phonon modes when the well width is very small while the confined modes play a more important role in a wider well due to the location of the electron wave function.As the well width increases,the cyclotron mass of magnetopolarons first increases to a maximum and then decreases either with or without the built-in electric field in the wurtzite structure and the built-in electric field slightly reduces the cyclotron mass.The variation of cyclotron mass in a zinc-blende structure is similar to that in a wurtzite structure.With the increase of external magnetic field,the cyclotron mass of polarons almost linearly increases.The cyclotron frequency of magnetopolarons is also discussed.     

Magnetic properties of a Pt/Co2FeAl/MgO structure with perpendicular magnetic anisotropy

Microstructures and magnetic properties of Ta/Pt/Co 2 FeAl（CFA）/MgO multilayers are studied to understand perpendicular magnetic anisotropy（PMA） of half-metallic full-Heusler alloy films.PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope.It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA.The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature.At the intersection points,the decreasing slope of the saturation magnetization（M s） changes because of the conversions.The dependence of M s on the annealing temperature and MgO thickness is also studied.     

Photodetachment of H-near a metal surface

By using the closed orbit theory, the photodetachment cross section of H^- near a metal surface is derived and calculated. The results show that the metal surface has great influence on the photodetachment process. As the ion-surface distance is very large, the influence of the electrostatic image potential caused by the metal surface becomes small and can be neglected. The period, action, and length of the detached electron＇s closed orbit are nearly the same as the case of the photodetachment of H^- near an elastic interface. However, with the decrease of the ion-surface distance, the influence of the metal surface becomes significant. The amplitude of the oscillation in the photodetachment cross section becomes complicated. Each resonance peak in the Fourier transformed cross section is associated with one electron＇s closed orbit. Unlike the case of the photodetachment of H^- near an elastic interface, the length of the closed orbit does not equal the twice distance between the ion and the surface. But with the increase of the ion-surface distance, the length of the closed orbit approaches the case of the closed orbit near an elastic interface, which suggests the correctness of our method. This study provides a new understanding on the photodetachment process of H^- in the presence of a metal surface.     

Compound buried layer SOI high voltage device with a step buried oxide

A silicon-on-insulator (SOI) high performance lateral double-diffusion metal oxide semiconductor (LDMOS) on a compound buried layer (CBL) with a step buried oxide (SBO CBL SOI) is proposed.The step buried oxide locates holes in the top interface of the upper buried oxide (UBO) layer.Furthermore,holes with high density are collected in the interface between the polysilicon layer and the lower buried oxide (LBO) layer.Consequently,the electric fields in both the thin LBO and the thick UBO are enhanced by these holes,leading to an improved breakdown voltage.The breakdown voltage of the SBO CBL SOI LDMOS increases to 847 V from the 477 V of a conventional SOI with the same thicknesses of SOI layer and the buried oxide layer.Moreover,SBO CBL SOI can also reduce the self-heating effect.     

Magnetic properties of a Pt/Co₂ FeAl/MgO structure with perpendicular magnetic anisotropy

Microstructures and magnetic properties of Ta/Pt/Co 2 FeAl(CFA)/MgO multilayers are studied to understand perpendicular magnetic anisotropy(PMA) of half-metallic full-Heusler alloy films.PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope.It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA.The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature.At the intersection points,the decreasing slope of the saturation magnetization(M s) changes because of the conversions.The dependence of M s on the annealing temperature and MgO thickness is also studied.     

Novel high-voltage power lateral MOSFET with adaptive buried electrodes

A new high-voltage and low-specific on-resistance (R on,sp ) adaptive buried electrode (ABE) silicon-on-insulator (SOI) power lateral MOSFET and its analytical model of the electric fields are proposed. The MOSFET features are that the electrodes are in the buried oxide (BOX) layer, the negative drain voltage V d is divided into many partial voltages and the output to the electrodes is in the buried oxide layer and the potentials on the electrodes change linearly from the drain to the source. Because the interface silicon layer potentials are lower than the neighboring electrode potentials, the electronic potential wells are formed above the electrode regions, and the hole potential wells are formed in the spacing of two neighbouring electrode regions. The interface hole concentration is much higher than the electron concentration through designing the buried layer electrode potentials. Based on the interface charge enhanced dielectric layer field theory, the electric field strength in the buried layer is enhanced. The vertical electric field E I and the breakdown voltage (BV) of ABE SOI are 545 V/μm and -587 V in the 50 μm long drift region and the 1 μm thick dielectric layer, and a low R on,sp is obtained. Furthermore, the structure also alleviates the self-heating effect (SHE). The analytical model matches the simulation results.     

The effect of interface hopping on inelastic scattering of oppositely charged polarons in polymers

The inelastic scattering of oppositely charge polarons in polymer heterojunctions is believed to be of fundamental importance for the light-emitting and transport properties of conjugated polymers. Based on the tight-binding SSH model, and by using a nonadiabatic molecular dynamic method, we investigate the effects of interface hopping on inelastic scattering of oppositely charged polarons in a polymer heterojunction. It is found that the scattering processes of the charge and lattice defect depend sensitively on the hopping integrals at the polymer/polymer interface when the interface potential barrier and applied electric field strength are constant. In particular, at an intermediate electric field, when the interface hopping integral of the polymer/polymer heterojunction material is increased beyond a critical value, two polarons can combine to become a lattice deformation in one of the two polymer chains, with the electron and the hole bound together, i.e., a self-trapped polaron-exciton. The yield of excitons then increases to a peak value. These results show that interface hopping is of fundamental importance and facilitates the formation of polaron-excitons.     

Photoionization microscopy of hydrogen atom near a metal surface

We have studied the ionization of Rydberg hydrogen atom near a metal surface with a semiclassical analysis of photoionization microscopy. Interference patterns of the electron radial distribution are calculated at different scaled energies above the classical saddle point and at various atom-surface distances. We find that different types of trajectories contribute predominantly to different manifolds in a certain interference pattern. As the scaled energy increases, the structure of the interference pattern evolves smoothly and more types of trajectories emerge. As the atom approaches the metal surface closer, there are more types of trajectories contributing to the interference pattern as well. When the Rydberg atom comes very close to the metal surface or the scaled energy approaches the zero field ionization energy, the potential induced by the metal surface will make atomic system chaotic. The results also show that atoms near a metal surface exhibit similar properties like the atoms in the parallel electric and magnetic fields.     

Study on the degradation of NMOSFETs with ultra-thin gate oxide under channel hot electron stress at high temperature

This paper studies the degradation of device parameters and that of stress induced leakage current (SILC) of thin tunnel gate oxide under channel hot electron (CHE) stress at high temperature by using n-channel metal oxide semiconductor field effect transistors (NMOSFETs) with 1.4-nm gate oxides. The degradation of device parameters under CHE stress exhibits saturating time dependence at high temperature. The emphasis of this paper is on SILC of an ultra-thin-gate-oxide under CHE stress at high temperature. Based on the experimental results, it is found that there is a linear correlation between SILC degradation and V_h degradation in NMOSFETs during CHE stress. A model of the combined effect of oxide trapped negative charges and interface traps is developed to explain the origin of SILC during CHE stress.     

Comparative study of electrical characteristics for n-type 4H–SiC planar and trench MOS capacitors annealed in ambient NO

The interface properties and electrical characteristics of the n-type 4H-SiC planar and trench metal–oxide–semiconductor(MOS) capacitors are investigated by measuring the capacitance voltage and current voltage. The flat-band voltage and interface state density are evaluated by the quasi-static method. It is not effective on further improving the interface properties annealing at 1250℃ in NO ambient for above 1 h due to the increasing interface shallow and fast states.These shallow states reduce the effective positive fixed charge density in the oxide. For the vertical MOS capacitors on the(1120) and(1100) faces, the interface state density can be reduced by approximately one order of magnitude, in comparison to the result of the planar MOS capacitors on the(0001) face under the same NO annealing condition. In addition, it is found that Fowler–Nordheim tunneling current occurs at an oxide electric field of 7 MV/cm for the planar MOS device.However, Poole–Frenkel conduction current occurs at a lower electric field of 4 MV/cm for the trench MOS capacitor. This is due to the local field crowded at the trench corner severely causing the electrons to be early captured at or emitted from the SiO_2/Si C interface. These results provide a reference for an in-depth understanding of the mobility-limiting factors and long term reliability of the trench and planar SiO_2/Si C interfaces.     

Mn Nanowhiskers of a Novel Hexagonal Phase Grown from Hydrogen Activated Laves Phase Alloys

With the aid of hydrogenation/dehydrogenation, nanorod whiskers of transition metal Mn can grow spontaneously from Zrl_xTi~MnCr Laves phase alloys at room temperature. The finding introduces a distinguishingly different element into metal whisker family, and provides a potential technique for fabrication of one-dimensional metal nanostructures. Moreover, it is found that the segregated Mn in whiskers forms a novel hexagonal structure, which partially fulfills the long predicted allotropic form and adds more complexity to the structures of Mn.     

Shear-horizontal transverse-electric seismoelectric waves in cylindrical double layer porous media

The shear-horizontal(SH) waves excited by the shear source in a borehole are easy to analyze due to the simple waveform. The borehole-side structures make the formation properties discontinuous. We consider a cylindrical double layer structure and study the borehole shear-horizontal and transverse-electric(SH-TE) seismoelectric waves. We first derive the expressions of the basic field quantities, and simulate the acoustic field and electric field using the real axis integral method. Compared with the wave fields of an infinitely homogeneous porous medium outside the borehole, the cylindrical layered structure makes the multi-mode cylindrical Love waves and their accompanying electric fields excited.Next, in order to study the interface response law of the inducing electric fields, we use the secant integral method to calculate the interface converted electromagnetic waves and analyze the causes of each component. It is found that an interface response occurs each time the SH wave impinges the interface in the layered porous medium. The results show that the SH-TE mode has a potential application for borehole-side interface detection in geophysical logs.     

Dynamical study on charge injection and transport in a metal/polythiophene/metal structure

The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene （PT）/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PT. We demonstrate that the dynamical formation of the wave packet sensitively depends on the strength of applied voltage, the electric field, and the contact between PT and electrode. At a strength of the electric field more than 3.0 × 10^4 V/cm, the carriers can be ejected from the PT into the right electrode. At an electric field more than 3.0 × 10^5 V/cm, the wave packet cannot form while it moves rapidly to the right PT/metal interface. It is shown that the ejected quantity of charge is noninteger.