J C Inkson

Electron states in a two-dimensional ring - an exactly soluble model

An exactly soluble model for a two-dimensional ring is proposed. Using this model, we have obtained analytically the energy spectrum and wavefunctions for a ring in the presence of a uniform magnetic field and a thin magnetic flux. The model can also describe quantum dots, anti-dots, one-dimensional rings and straight two-dimensional wires, which provides an integrated picture for the electron states and their magnetic field response in these geometries. The simplicity and the flexibility of the model make it an ideal tool for the modelling of the Aharonov - Bohm effects and the persistent currents in quantum rings.

Longitudinal-optic-transverse-optic vibrational mode splittings in tetrahedral network glasses

Abstract This paper presents a microscopic theory of longitudinal-optic-transverse-optic vibrational mode splittings in tetrahedral network glasses. The complete dynamical equations for the vibrational modes of the glass are used to show that the long-range Coulomb interactions can generate a uniform effective electric field which acts as an ordering force and overcomes the effects of the disorder in the glass to produce well defined longitudinal and transverse vibrational modes. The frequencies of these modes differ from the frequencies of vibrational modes calculated using short-range forces only because of the additional force exerted on the atoms by the uniform effective electric field.

Many-body effects at metal-semiconductor junctions. I. Surface plasmons and the electron-electron screened interaction

The electron-electron screened interaction near the metal-semiconductor junction is calculated analytically by the introduction of model bulk dielectric functions which contain all of the essential energy and wavelength dependent features of the real dielectric functions of the metal and semiconductor. The poles of the interaction give the dispersion relations for the surface plasmon excitations at the junction and these are studied for various parameters of the two bulk media. It is shown that there are two possible plasmon modes characteristic of bimetal and metal-classical dielectric interfaces. Also, the role of surface plasmons in Schottky barriers is discussed.

The electron-electron interaction near an interface

Abstract The application of many body techniques to interfaces is restricted by the labour involved in obtaining a screened interaction which is valid in the interface region. To be realistic this must contain not only non-locality but also the extra poles in energy corresponding to interface excitations. An approximation is presented which obtains the interaction in terms of the bulk dielectric properties of the two media but still has the necessary properties mentioned above. The extra energy poles are examined and shown to correspond to surface plasmon type excitations at the interface. The asymptotic form of the exchange and correlation potential is calculated using the non-local screened interaction and shown to correspond to the classical image potential at large distances from a metal surface.

The effect of electron interaction on the band gap of extrinsic semiconductors

The change in the band gap of a semiconductor due to high doping is considered in the limit where the free carriers form a degenerate gas. In contrast to previous treatments, the effect of the change in the electron interaction on the whole band structure is considered within a self energy framework so that the difference between valence and conduction bands can be found more accurately. The results obtained are significantly different, in some aspects, from earlier work. This is discussed and the application to experiment reviewed.

Schottky barriers and plasmons

The changes in the electron exchange and correlation potential are related to the collective excitation at the interface of a metal semiconductor junction. They are shown to change discontinuously across the band gap, and the possible effects on the barrier formation are discussed. The possibility of surface superconductivity through exciton and plasmon exchange is considered briefly.

dc electroluminescence in copper‐free ZnS:Mn thin films. II. A dielectric breakdown theory of instability

The occurrence of localized destructive breakdown (LDB) is a feature of direct coupled thin‐film electroluminescence (DCTFEL) which has been attributed in the past to variations in applied field or threshold voltage caused by geometrical artifacts introduced during film deposition. However, in a companion paper it has been reported that this view of LDB is inconsistent with observations; instead there are strong indications that both LDB and DCTFEL are natural consequences of dielectric breakdown in ZnS:Mn. In this paper, the O’Dwyer theory of dielectric breakdown is applied to DCTFEL in ZnS:Mn with the aid of a simple computational equilibrium model. It is found that with reasonable assumed values for basic electronic parameters, current‐controlled negative resistance (CCNDR) is expected in the normal DCTFEL current density regime. Localized (filamentary) conduction is, of course, a well‐known consequence of CCNDR and the profound implications of this for EL are explored in some detail. It becomes clear that a number of poorly understood features of practical DCEL devices arise quite naturally from this dielectric breakdown theory; examples are premature brightness saturation at near maximum efficiency, the coexistence of DCTFEL and LDB, and the factors affecting the balance of that coexistence. It is concluded that while the dielectric breakdown model of DCTFEL presently rests precariously on assumed parameter values, the qualitative predictive power of the theory gives it significant weight. In view of this, some of the implications for DCTFEL device design are explored.The occurrence of localized destructive breakdown (LDB) is a feature of direct coupled thin‐film electroluminescence (DCTFEL) which has been attributed in the past to variations in applied field or threshold voltage caused by geometrical artifacts introduced during film deposition. However, in a companion paper it has been reported that this view of LDB is inconsistent with observations; instead there are strong indications that both LDB and DCTFEL are natural consequences of dielectric breakdown in ZnS:Mn. In this paper, the O’Dwyer theory of dielectric breakdown is applied to DCTFEL in ZnS:Mn with the aid of a simple computational equilibrium model. It is found that with reasonable assumed values for basic electronic parameters, current‐controlled negative resistance (CCNDR) is expected in the normal DCTFEL current density regime. Localized (filamentary) conduction is, of course, a well‐known consequence of CCNDR and the profound implications of this for EL are explored in some detail. It becomes clear ...

Scattering matrix theory of transport in heterostructures

A scattering matrix formalism is developed for the transport of electrons in heterostructures. It is shown how the approach may be used to calculate transport properties in superlattices and non-periodic devices. The formalism is applied, within an empirical pseudopotential model, to the calculation of tunnel junction fluxes through a GaAs/AlAs double barrier structure. When a comparison of the analysis to a conventional one-band effective-mass model is made, significant deviations between the two approaches are found to result.

A new matrix method for tunnelling in heterostructures: Γ, X effects in single-barrier systems

The authors present the results on the band-structure effects in single-barrier tunnelling, calculated using a new scattering matrix method. Their results show that the transmission amplitude may be divided into two regions. The first is for electron energies in the band gap of the barrier material, where the transmission is found to be a single state property, with the Gamma state dominant. The appropriate barrier height, regardless of the direct/indirect nature of the barrier band gap, is the Gamma - Gamma band offset. The tunnelling behaviour is therefore single state like. The other regime is for electrons with energies above the barrier materials conduction band edge where, for indirect band-gap barriers, a sharp transition to an X dominated behaviour is observed. Coupling between the barrier Gamma and the X states are found in thin barriers and X well resonances are obtained. The single barrier transmission in this regime is therefore a multistate property.

Electron scattering from heterojunctions

The scattering of conduction electrons from the GaAs-Ga1-xAlxAs heterojunction is calculated for a number of alloy concentrations. It is shown that the excitation of evanescent states derived from the higher conduction minima play a major part in the scattering process. Substantial deviations from effective-mass theory are found. It is shown how the numerical results may be incorporated into an evaluation of quantum well and superlattice systems.