Surface Transverse Field Research Articles

Effect of Boro-Silicate Glass (BSG) Gate Dielectric with Antimony Surface Doping on Channel Transport of 4H-SiC Mosfets

In this work, we investigate the effect of Boro-silicate glass (BSG) gate dielectric in conjunction with Antimony (Sb) surface doped channels of lateral 4H-SiC MOSFETs. It has been reported that BSG gated 4H-SiC MOSFETs have a high channel mobility of ~100 cm2/V∙s for a wide range of surface transverse electric fields along with a large threshold voltage VT of ~5V in lightly doped p-epitaxial layers [1,2]. For vertical power MOSFETs with heavily doped p-wells, it is expected that BSG would cause an even further increase of VT (~10 V) which would be undesirable. Therefore in this work, our goal for combining the Sb surface doping process (demonstrated in our earlier works [3,4] and presented at ECSCRM 2014 [4]), with BSG gate dielectric was two-fold: (i) Tune VT to adequate value with high sub-threshold slope. (ii) Achieve high low-field channel mobility by Sb counter-doping while retaining the high-field mobility characteristics of BSG. The results from our experiments indicate that these goals were achieved. The 'Sb+BSG' process results in significant improvement of both low-field channel mobility to ~180cm2/V∙s (due to addition of Sb surface doping) and high-field channel mobility to ~90 cm2/V∙s (due to the BSG gate dielectric) along with a tuned threshold voltage of ~2V and a steeper sub-threshold slope. Lateral MOSFETs were fabricated on the Si-face of p-type 4H-SiC epitaxial layers doped at ~1x1016cm-3. Sb was implanted in the channel region with 80 keV at room temperature with dose of 2.5x1013cm-2, which results in a Gaussian profile with a depth of around 30nm below the surface of SiC. This was followed by post-implantation activation annealing at 1650°C using a graphitic carbon cap layer. Next, dry oxidation at 1150°C for 10 hours was performed followed by post-oxidation annealing using a planar diffusion source (Techneglas, GS-139) composed of boric oxide (B2O3) in a gas mixture of Ar (50sccm) and O2 (5sccm) at 950°C for 30 mins. Samples that received only boron annealing are referred to as 'BSG only' and samples underwent both Sb counter-doping and boron annealing are referred to as 'Sb+BSG'. Results for these samples are compared with standard NO-annealed devices in Table Ⅰ. The SIMS result in Fig. 1 shows B distributes throughout the oxide with a concentration of ~1x1022cm-3 and decreases as it reaches SiC. Threshold voltage and sub-threshold slope were characterized by Id-Vg measurement at room temperature and field-effect mobility was extracted from the transconductance of Id-Vg curve. Linear and log scale of Id-Vg curves in Fig. 2 and Fig. 3 demonstrate that 'Sb+BSG' tunes the threshold voltage to a more desirable value of ~2V along with a better sub-threshold slope than standard NO annealing. Fig. 4 shows a significant mobility improvement for 'Sb+BSG' at both high field due to the BSG passivation effect and low field due to the Sb counter-doping effect with a peak value of ~180cm2/V∙s compared to 'BSG only' with a peak mobility of ~140cm2/V∙s. In order to investigate the boron passivation effect on interface traps, C-V and constant capacitance deep level transient spectroscopy (CCDLTS) measurements were performed on the companion BSG capacitors. The interface trap density of 'NO' was determined to be ~2.5 times higher than that of 'BSG' for very shallow energy traps (<0.2 eV) from C-V measurements and ~1.5 times higher for the energy trap distributions centered at 0.15 eV and 0.39 eV by CCDLTS, as shown in Figs. 5 and 6. The mechanism of boron passivation has been suggested to be oxide stress relaxation by the reduction of required oxygen bonds due to the occupation of Si site by B [5]. In this presentation, further details of the nature of transport and mobility behavior in BSG gated channels will be presented as a function of temperature.

Phase transition behaviors of a ferroelectric thin film with long-range interactions

ABSTRACTWithin the framework of the mean-field approximation, the transverse-field Ising model is used to investigate the surface parameter modification of interaction constants and transverse fields on phase transition behaviors of a ferroelectric thin film with long-range interactions. The variation of Curie temperature as a function of the surface transverse field for different surface interaction constants or thickness is discussed. Meanwhile, the variation of Curie temperature as a function of the surface exchange interaction for different surface transverse fields is examined. In addition, the dependence of Curie temperature on the film thickness for different surface exchange interactions and surface transverse fields is obtained.

Transverse magnetic field of infinite line source placed on ground surface

An exact explicit expression is derived for the Sommerfeld integral describing the surface transverse magnetic field generated by an infinite line source placed on a plane air–earth boundary. The spatial distribution of the transverse magnetic field is given in series form, as a linear combination of exponential functions. The accuracy and convergence rate of the proposed formulation are investigated through numerical simulations.

Ferrimagnetic behaviors in a double-wall cubic metal nanotube

A double-wall cubic metal nanotube consists of the ferromagnetic spin-1 inner shell and spin-3/2 surface shell. It is of the ferrimagnetic exchange coupling between two shells. Considering the single-ion anisotropy and transverse field exist together, the magnetization, the initial susceptibility, the internal energy and the specific heat have been investigated by using the effective-field theory with correlations. Some interesting phenomena have been found in the thermal variations of the system. Magnetization appears two or three compensation points in certain parameters. It is an unconventional ferrimagnetic behavior in the nanotube. The shapes of total magnetization and the initial susceptibility are great influenced by the surface exchange coupling, surface single-ion anisotropy and surface transverse field. Some results of nanotube may have potential applications in different research fields, such as electronics, optics, mechanics, and even biomedicine and molecular devices.

Surface effects on magnetic and thermodynamic properties in nanoscale multilayer ferrimagnetic films

Magnetic and thermodynamic properties of a nanoscale multilayer ferrimagnetic films have been studied within the effective-field theory with correlations. The general formula for magnetization and internal energy is given. Some interesting results have been shown in the phase diagrams, for example two compensation points exist in the range of surface physical parameters. The competition among the surface exchange coupling, the surface single-ion anisotropy and the surface transverse field have great influences on the magnetization, the internal energy and the specific heat in the nanoscale multilayer ferrimagnetic films.

Parameter modifications in the phase diagrams of a ferroelectric nanoparticle described by the transverse field Ising model

Within the framework of the effective-field theory (EFT) with correlations, the differential operator technique has been used to study the phase diagrams of a ferroelectric nanoparticle described by the transverse field Ising model. The dependence of the phase diagrams on two types surface parameters modifications, modifications of the surface transverse field and the surface exchange interaction, is calculated numerically in the ( T c , J s ) coordinates or the ( T c , Ω s ) coordinates. The crossover features, from the ferroelectric-dominant phase diagram (FPD) to the paraelectric-dominant phase diagram (PPD), for interaction parameters of a ferroelectric nanoparticle with a size S are determined. Meanwhile, the critical behaviours are also examined for the ferroelectric nanoparticle system.

Epitaxy surface effect on the critical properties of a ferroelectric thin film

The characteristic properties, the critical surface transverse field Ωsc and the Curie temperature Tc, for an N-layer ferroelectric thin film with epitaxy surface layers Ns described by the transverse field Ising model have been studied by the differential operator technique within the framework of effective-field theory with correlations. The analytical equation for the phase diagrams of ferroelectric thin films is derived. The surface transverse field Ωs dependence of the Curie temperature Tc in the ferroelectric thin film with different epitaxy surface layers is calculated. Meanwhile the epitaxy surface layer number Ns dependence of the critical surface transverse field Ωsc and the Curie temperature Tc is also examined. The results show that the critical properties depend heavily on modifications of interchange interactions and transverse fields in the epitaxy surface layer.

Surface effects on a multilayer and multisublattice cubic nanowire with core/shell

A multilayer and multisublattice cubic nanowire is studied based on a shell/core and the effective-field theory. The formulas of the longitudinal and transverse magnetization for each sublattice of the nanowire are given. The surface parameters have intense effects on the magnetizations and phase diagrams (phase transition temperatures and compensation temperatures) of the system. Two compensation points do exist for certain values of the surface transverse field, the surface single-ion anisotropy and the surface exchange coupling in the system. This interesting phenomenon may be potential applications in information storage technology.

Effects of surface modification on the critical behaviour in multiple-surface-layer ferroelectric thin films

Using the usual mean-field theory approximation, the critical behaviour (i.e. the Curie temperature Tc and the critical surface transverse field Ω sc ) in a multiple-surface-layer ferroelectric thin film is studied on the basis of the spin- transverse Ising model. The dependence of the Curie temperature Tc on the surface transverse field Ω s and the surface layer number Ns are discussed in detail. Meanwhile the dependence of the critical surface transverse field Ω sc on the surface layer number Ns is also examined. The numerical results indicate that the critical behaviour of ferroelectric thin films is obviously affected by modifications of the surface transverse field Ω s and surface layer number Ns.

Surface Effects on Phase Diagram and Magnetization of a Mixed Spin-3/2 and Spin-5/2 Ising Multilayers

The magnetizations of multilayers thin film described by the transverse Ising model have been investigated within the framework of the effective-field theory with correlations. The influence of the surface exchange coupling and the surface transverse fields on the magnetization and the phase transition temperature are studied respectively. Within a certain parameter, the magnetization obviously exhibit two compensation temperatures. Two compensation temperatures intersect and disappear with the surface exchange coupling or the surface transverse fields increasing.

Surface phase transitions of the transverse Ising model with modified surface–bulk coupling

The phase diagram of the three-dimensional transverse Ising system with antiferromagnetic intrasurface J S and surface–bulk J ⊥ interactions modified with respect to the ferromagnetic bulk exchange interaction J B is studied by the use of an effective field method in the framework of a single-site cluster theory. In this investigation, the state equations are derived by means of differential operator technique. Using these coupled equations within the four-layer approximation, it has been shown that the new parameter J ⊥ strongly affects the phase diagram obtained recently in the case J ⊥ = J B. Indeed, our calculations reveal some qualitatively interesting features both in the absence and in the presence of the surface and bulk transverse fields.

Phase Transition Properties of a Ferroelectric Superlattice with Surface Modification

The phase diagrams of a ferroelectric superlattice with finite alternating layers are investigated by using the transverse Ising model within the mean-field approximation. The effects of surface modification are introduced through a surface exchange interaction constant and a surface transverse field parameter. The results indicate that the features of the phase diagrams can be greatly modified by changing the transverse Ising model parameters. In addition, the crossover features of the inside transverse field parameters from the ferroelectric dominant phase diagram to the paraelectric dominant phase diagram are determined for a finite alternating superlattice.

The diluted transverse Ising model with competing bulk and surface ordering

AbstractThe phase diagram of the three‐dimensional transverse Ising system with competing surface and bulk exchange interactions is studied by the use of an effective‐field method within the framework of a single‐site cluster theory. In addition to this pure case, which shows qualitatively interesting features, we investigated the effects of the bond dilution on the obtained phase diagram. In particular, we studied the influence of the surface dilution parameter on the surface transitions. We find a number of characteristic behaviours of the surface both in the absence and in the presence of the surface transverse field. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Thickness dependence of the dielectric function of ferroelectric thin films

AbstractA Green's function technique for a modified Ising model in a transverse field is applied, which allows to calculate the real and the imaginary parts of the dielectric function ϵ(k, E) for ferroelectric thin films. Compared to bulk materials the frequency of the soft‐mode in thin film is reduced whereas the damping is enhanced. The dependence of ϵ(k, E) on temperature and film thickness is obtained for k = 0 numerically. It is demonstrated, that the maximum of the dielectric function decreases with decreasing film thickness. The temperature, where the dielectric function offers a maximum, can decrease or increase depending on the strength of the surface transverse field and the exchange interaction parameter. Due to stronger damping effects in thin films the peak in the dielectric function becomes more diffuse when the film thickness decreases. The results are in reasonable qualitative agreement with experimental data for different ferroelctrics. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

New aspects of magnetic properties in a transverse Ising thin film

The magnetic properties of a transverse Ising thin film are investigated by the use of the two theoretical frameworks, namely the standard mean-field theory and the effective field theory better than the mean-field theory. Some new aspects of the magnetic properties have been clarified firstly by including the modification of both surface exchange interaction and surface transverse field. The phase diagram, magnetization and initial susceptibility of a thin film can exhibit many characteristic behaviors, depending on the ratio between the surface transverse field and the bulk one.

The effects of bulk and surface fields on the phase diagram of a transverse Ising thin film

AbstractThe phase diagram of a transverse Ising thin film is investigated by the use of two theoretical frameworks, namely the standard mean field theory and the effective field theory. The effects of the ratio p between the bulk and surface transverse fields on the critical temperature are discussed by including the modification of surface exchange interaction. Some characteristic features are found in the phase diagrams when the ratio p increases from p = 1.0. They are enhanced for the film with thickness L smaller than 5.0. In particular, the critical ratio at which the critical temperature of the film with a finite transverse field reduces to zero, being independent of L, exhibits a linear relation when it is plotted against the modification of surface exchange interaction.

Ferromagnetic transitions of a spin-one Ising film in a surface and bulk transverse fields

Using the effective field theory method, we have calculated the Curie temperature of a spin-one Ising ferromagnetic film in a surface and bulk transverse fields. Numerical calculations give phase diagrams under various parameters. Surface exchange enhancement is considered. The dependence of the critical transverse field on film thickness, and phase diagrams in the fields, critical surface transverse field versus the bulk one are presented.

Order–disorder layering transitions in a variable transverse field

The effect of a variable surface transverse magnetic field Ω s , on the order–disorder layering transitions of an Ising spin − 1 2 model is investigated using mean field theory (MF) and finite cluster approximation (FC). For a film with finite thickness formed with N layers, each layer z transits at a fixed temperature from the ordered to the disordered phase, under the effect of the transverse magnetic field Ω(z)=Ω s /z α , (z=1, …, N) . These order–disorder layering transitions are absent for α=0 even if increasing the temperature and/or the surface transverse magnetic field. On the other hand, the dependency of longitudinal and transverse magnetisations on temperature and surface transverse magnetic field are illustrated for a fixed value of the exponent α.

Phase transition of a transverse semi-infinite spin-1 Ising model with crystal field

The effect of the surface and bulk transverse fields on the phase diagrams of a semi-infinite spin-1 ferromagnetic Ising model with a crystal field is investigated within a finite cluster approximation with an expansion technique for cluster identities of spin-1 localized spin systems. Phase diagrams are determined as a function of the ratio of bulk and surface transverse fields and the ratio of bulk and surface crystal fields. However, the system exhibits a variety of phase transitions and multi-critical points. A dead layer appears in a special region of the space parameters.

Effects of multi-surface modification on Curie temperature of ferroelectric films

Within the framework of mean field theory, we study the effects of multi-surface modification on the Curie temperature of ferroelectric films using the transverse Ising model. The general nonlinear equations for Curie temperature of multi-surface ferroelectric films with arbitrary exchange constants and transverse fields are derived by the transfer matrix method. As an example, we consider an (l,n,l) film consisting of l top surface layers, n bulk layers and l bottom surface layers. Two types of surface modification, modifications of a surface exchange constant and a surface transverse field, are taken into account. The dependence of Curie temperature on the surface layer numbers, bulk layer numbers, surface exchange constants, surface transverse fields and bulk transverse fields is discussed.