摘要:

Non-equilibrium Green function theory is formulated to meet the three main challenges of high bias quantum device modeling: self-consistent charging, incoherent and inelastic scattering, and band structure. The theory is written in a general localized orbital basis using the example of the zinc blende lattice. A Dyson equation treatment of the open system boundaries results in a tunneling formula with a generalized Fisher-Lee form for the transmission coefficient that treats injection from emitter continuum states and emitter quasi-bound states on an equal footing. Scattering is then included. Self-energies which include the effects of polar optical phonons, acoustic phonons, alloy fluctuations, interface roughness, and ionized dopants are derived. Interface roughness is modeled as a layer of alloy in which the cations of a given type cluster into islands. Two different treatments of scattering; self-consistent Born and multiple sequential scattering are formulated, described, and analyzed for numerical tractability. The relationship between the self-consistent Born and multiple sequential scattering algorithms is described, and the convergence properties of the multiple sequential scattering algorithm are numerically demonstrated by comparing with self-consistent Born calculations. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365394

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Current transport and ballistic electron emission microscopy (BEEM) studies have been carried out on metal contacts fabricated on chemically etchedn-ZnSe epitaxial layers grown by molecular beam epitaxy. The contact materials Ag, Sb, Au, Ge/Au, Sn, Ni, and Pd form one or more barrier heights out of the following seven discrete values: 0.90, 1.20, 1.32, 1.50, 1.67, 1.80, and 2.10±0.04 eV observed to date. BEEM work carried out on Au/n-ZnSe systems has identified four levels 1.32 [Morgan &etal;, J. Appl. Phys.79, 1532 (1996)], 1.50, 1.67 [Coratger &etal;, Phys. Rev. B15, 2357 (1995)] and 1.80 eV to date, confirming Fermi-level pinning at different positions. Schottky barrier formation at metal/n-ZnSe systems cannot be explained by the simple Schottky model. The strong Fermi-level pinning observed could be due to bulk and/or surface defects of the ZnSe material. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365395

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Previous current–voltage studies of In contacts deposited on atomically clean (intimate)In53Ga47As(100)have indicated the potential to “select” barrier heights in this materials system by cryogenic processing. Soft x-ray photoemission spectroscopy was used to determine the electronic and chemical nature of these interfaces, as a function of formation temperature. Metallization at room temperature results in a predominantly three-dimensional mode of growth, accompanied by the outdiffusion of As. Low temperature metallization appears to reduce clustering and inhibit As outdiffusion. It is proposed that the distribution of surface states and the fermi level pinning position are altered by the changes that occur in the geometry and bonding of the interface at low temperature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365377

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A fast and robust iterative method for obtaining self-consistent solutions to the coupled system of Schro¨dinger’s and Poisson’s equations is presented. Using quantum mechanical perturbation theory, a simple expression describing the dependence of the quantum electron density on the electrostatic potential is derived. This expression is then used to implement an iteration scheme, based on a predictor-corrector type approach, for the solution of the coupled system of differential equations. We find that this iteration approach simplifies the software implementation of the nonlinear problem, and provides excellent convergence speed and stability. We demonstrate the approach by presenting an example for the calculation of the two-dimensional bound electron states within the cross section of a GaAs-AlGaAs based quantum wire. For this example, the convergence is six times faster by applying our predictor-corrector approach compared to a corresponding underrelaxation algorithm. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365396

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Energy eigenvalues and energy shifts are calculated for triangular and arrowhead-shapedGaAs/Ga0.6Al0.4Asquantum wires taking into account the finite value of the barrier potential. Calculations were made by using the eigenfunctions of an infinite-barrier right-angled isosceles triangular wire. Calculated values are compared with available experimental results. An equivalence relation is also examined for the estimation of eigenvalues of triangular and arrowhead-shaped quantum wires by knowing the values for rectangular wires. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365361

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Using a variational procedure, within the effective mass-approximation, we calculate the binding energy of a shallow-donor impurity in a rectangular cross-sectional area of a GaAs quantum-well wire, under the action of an electric field applied perpendicular to one of the interfaces, assuming an infinite-confinement potential. We study the binding energy of the donor impurity as a function of the system geometry, the applied electric field, and the donor-impurity position. It was found that the presence of the electric field breaks down the degeneracy of the states for impurities symmetrically positioned within the structure. Our results for a large length of one side of the cross-sectional area coincide quite well with previous results in quantum wells. We show, unambiguously, that the impurity binding energy depends strongly not only on quantum confinement, but also on the applied electric field and on the distribution of impurities inside the quantum-well wires; these aspects must be taken into account in the quantitative understanding of optical phenomena related to shallow impurities when an electric field is applied. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365362

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Carrier relaxation in self-assembled quantum dots due to Coulomb interaction with two dimensional (2D) carriers is studied theoretically. Auger coefficients for carrier relaxation rates are calculated in the dipole approximation for Coulomb interaction. The dipole approximation allows one to derive selection rules for Auger relaxation in a cylindrical quantum dot, and to describe a general picture of Auger relaxation via energy levels in self-assembled quantum dots. A numerical example for InAs/GaAs self-assembled quantum dots demonstrates that the Auger effect may lead to relaxation times in the order of 1–10 ps at 2D carrier densities of1011–1012 cm−2.This result demonstrates the possibility of fast carrier relaxation in quantum dots if the carrier density in the surrounding barrier is sufficiently high. Analytical formulas for Auger coefficients are derived for moderate temperatures of the 2D carriers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365363

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Direct and Fowler-Nordheim tunneling through ultra-thin gate dielectrics is modeled based on an approach for the transmission coefficient (TC) of a potential barrier that is modified by the image force. Under the constraint of equal actions the true barrier is mapped to a trapezoidal pseudobarrier resulting in a TC very close to the numerical solution of the Schro¨dinger equation for all insulator thicknesses and for all energies of the tunneling electron. The barrier height of the pseudopotential is used as a free parameter and becomes a function of energy in balancing the actions. This function can be approximated by a parabolic relation which makes the TC of arbitrary barriers fully analytical with little loss of accuracy. The model was implemented into a multidimensional device simulator and applied to the self-consistent simulation of gate currents in metal-oxide-semiconductor (MOS) capacitors with gate oxides in the thickness range 15 Å–42 Å. Excellent agreement with experimental data was obtained using a thickness-independent tunnel massmox=0.42 m0. Thanks to the CPU-time efficiency of the method the simulation of a complete MOS-field-effect-transistor with dominating gate current becomes possible and shows the potential for further applications. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365364

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The structure and magnetic properties ofNdMn2(Ge1−xSix)2compounds(x=0–1.0)have been investigated. All the compounds crystallize inThCr2Si2-type structure. Substitution of Si for Ge leads to a linear decrease of the lattice constants and the unit-cell volume. With increasing temperature, for the compounds withx⩽0.5,both spin reorientation and ferromagnetic– paramagnetic transition are observed as well atTrandTC(Mn),respectively. The spin reorientation temperatureTrand the Curie temperatureTC(Mn)decrease linearly with Si content from 215 and 339 K atx=0–40and 306 K atx=0.5,respectively. In compounds with0.3<x⩽0.5the ferromagnetic component and the antiferromagnetic component may coexit. For compounds withx⩾0.6the ferromagnetic–antiferromagnetic and the antiferromagnetic–paramagnetic transition are observed and the Curie temperatureTC(Nd)decreases monotonically while the Ne´el temperatureTN(Mn)increases monotonically with Si content. A tendentious spin phase diagram has been obtained. The saturation magnetization at 1.5 K decreases first, goes through a minimum atx=0.5,and then increases again. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365191

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Magnetic domains in the remanent magnetization state of obliquely evaporated recording media Co–CoO films were studied by spin-polarized scanning electron microscopy. Inverse domains densely distributed in the media were found to have a closure-domainlike structure at the surface to reduce the magnetostatic energy. The size of the inverse domains depends on the direction of the external magnetic fields that were applied when the remanent states were formed. Using these results, the relationship between the inverse domains and the carrier-to-noise ratio for this kind of recording media is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365365

出版商:AIP    

年代:1997

数据来源: AIP