Bandstructure matching at a heterojunction interface

An analytic theory for the matching of the bandstructure of different crystals at the interface of a heterojunction is presented. The Generalized Wannier functions serve as a basis. For a simple uniform band, the Hamiltonian matrix elements then reduce to the k-space Fourier coefficients of the bandstructure along the superlattice direction. The technique therefore accounts for non-effective mass effects, and the lower and upper valleys, and enables us to invoke both the quasi-k-space periodicity together with the spatial variations of the bandstructure. The superlattice Hamiltonian is a system of difference equations taking the form of a band matrix. A new definition of current not based on the effective-mass is introduced for this higher-order Schroedinger equation. The enforcement of the continuity of the elemental currents leads to analytic connection rules for the overlap Hamiltonian matrix elements. A maximum transparency for all energies is achieved only for geometrically related bandstructures. Non-effective-mass effects are demonstrated in resonant-tunneling structures. The technique presented offers new theoretical insights together with efficient numerical tools for the study of non-effective-mass superlattices.     

Electron self-energy effect on a heterojunction bipolar transistor at T=0

An electron self-energy effect on a graded-gap heterojunction bipolar transistor at T=0 is considered. It is found that two competing mechanisms affect the collector current vs. emitter base bias voltage relations: (I) threshold voltage lowering for electron injection from emitter to base improves it: while (II) a decelerating field on injected minority carriers in the base degrades it. In a sufficiently large built-in field in the graded-gap base, negative transconductance appears as a result of the effect (I).     

Microscopic investigation of the band discontinuities at the silicon-germanium heterojunction interface

The formation of interface energy band discontinuities has been directly monitored on Ge-covered Si(111) surfaces with photoemission spectroscopy using synchrotron radiation. The final magnitude of the band discontinuities is not consistent with the linear combination of dipole-layers which leads to the “electron affinity rule”. Strong modifications of the local density of states occur during the formation of the heterojunction and the experiments indicate that the interface is abrupt on a microscopic scale.     

Electron transport via local polarons at interface atoms

Electronic transport is profoundly modified in the presence of strong electron-vibration coupling. We show that in certain situations, the electron flow takes place only when vibrations are excited. By controlling the segregation of boron in semiconducting Si(111)-square root 3 x square root 3 R 30 degrees surfaces, we create a type of adatom with a dangling-bond state that is electronically decoupled from any other electronic state. However, probing this state with scanning tunnelling microscopy at 5 K yields high currents. These findings are rationalized by ab-initio calculations that show the formation of a local polaron in the transport process.     

Electron correlations observed through intensity interferometry

Intensity interferometry was applied to study electron correlations in doubly ionizing ion-atom collisions. In this method, the probability to find two electrons emitted in the same double ionization event with a certain momentum difference is compared to the corresponding probability for two uncorrelated electrons from two independent events. The ratio of both probabilities, the so-called correlation function, is found to sensitively reveal electron correlation effects, but it is rather insensitive to the collision dynamics.     

Electron work function of aluminum nanowire at the interface with a dielectric medium

The influence of the environment permittivity on the electron work function of an aluminum nanowire has been estimated within the electron-density formalism for the first time.     

Quantum oscillations at a Ga0.47In0.53AsInP heterojunction interface

We report the observation of a two dimensional gas of high mobility electrons at the interface of a Ga_0.47In_0.53AsInP heterojunction grown by MOCVD. The two dimensional electron concentrations and effective mass are determined by Shubnikov-de Haas studies, and compared with theoretical predictions. Evidence of an enhancement of the g-factor is observed. We also report observations of very pronounced quantum Hall steps as seen in GaAs-GaAlAs heterojunctions.     

异质结界面电荷对突变InP/InGaAs异质结双极晶体管热场发射影响研究

异质结界面电荷的存在改变了异质结的内建势, 这引起了界面势垒尖峰高度和形状的扰动, 从而使异质结界面载流子的输运产生相应的变化, 最终导致异质结双极晶体管 (HBT) 性能的改变. 基于热场发射-扩散模型, 对异质结界面电荷对InP/InGaAs HBT性能的改变做了研究, 得到结论是正极性的界面电荷有利于InP/InGaAs HBT的直流和高频特性的改善, 而负极性的界面电荷则使器件的直流和高频特性变差. 关键词： InP/InGaAs异质结双极晶体管 界面电荷 内建势 热场发射     

Electron lifetime in a Shockley-type metal-organic interface state

The lifetimes of electrons at the interface between 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) and Ag(111) have been studied by means of time- and angle-resolved two-photon photoemission. We observe a dispersing unoccupied state 0.6 eV above the Fermi level with an effective electron mass of 0.39m{e} at the Gamma[over ] point. The short lifetime of 54 fs is indicative of a large penetration of the wave function into the metal. Supported by model calculations this interface state is interpreted as predominantly arising from an upshift of the occupied Shockley surface state of the clean metal due to the interaction with the PTCDA overlayer.     

Overlayer systems: Suitable samples for probing heterojunction interface properties

In this paper we report electronic structure calculations for Ge-(110) GaAs heterostructures. Our results demonstrate that Ge-(110) GaAs overlayer s ystems should be suitable samples for experimental investigations of heterojunction interface properties. We find that a 3 Ge-(110) GaAs overlayer system shows all bound interface states characteristic for the (110) Ge-GaAs heterojunction. Interface-induced resonances or semiresonances occur strongly enhanced in the overlayer system as compared to the true heterojunction. The wavevector-resolved weighted layer density of states at the Brillouin zone center, for example, shows a salient structure of interface-induced density peaks which should readily be accessible to normal emission ARUPS experiments.     

Apparent slip at a polymer-polymer interface

We consider a planar interface between strongly-segregated homopolymers subjected to steady shear in the plane of the interface. We develop a constitutive equation for stress relaxation in an inhomogeneous system for chains obeying Rouse dynamics. Using this equation, the interfacial viscosity for a symmetric blend is found to be in agreement with a scaling prediction due to de Gennes, where is the bead friction coefficient, b is the segment length, is the segment volume and is the Flory-Huggins interaction parameter driving the phase separation. We generalize our results to asymmetric blends and describe a phenomenological extension to entangled melts. Received: 18 August 1997 / Received in final form: 1 December 1997 / Accepted: 2 December 1997     

Magnetic polaritons at a superconductor-ferromagnet interface

The propagation of surface electromagnetic waves at the interface between a high-temperature superconductor and a ferromagnet is considered. Dispersion relations are derived for transverse electric and transverse magnetic surface eigenwaves in the case of various orientations of the crystallographic axes of the anisotropic superconductor with respect to the direction of the surface wave vector. A nonreciprocal character of the propagation of transverse electric polaritons is revealed, as well as a significant dependence of dispersion characteristics and the penetration depth on the external magnetic field.