In this article we review the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers.

Linear and nonlinear optical properties of semiconductor quantum wells

Quantum transport equation for electric and magnetic fields

The electron transport properties of metallic glasses

Publisher Summary This chapter presents an overview of several theoretical approaches and experimental measurement techniques for determining band offset values and discuss the experimental and theoretical data reported for a number of specific heterojunction systems. It also evaluates the credibility and accuracy of the experimental measurements and provides a tabulation of reliable band offset values for as many heterojunctions as possible. Among the most important physical parameters for a given heterojunction system are the conduction- and valence-band offsets; indeed, the quality and even the feasibility of heterojunction device concepts often depend crucially on the values of these band offsets. The band offset is defined simply as the discontinuity in the band edge at the interface between two semiconductors. A number of current theories seem to yield band offset values in reasonable agreement with experiment, even though the physical ideas underlying these theories can be quite different. These ideas include electron affinities, Schottky barrier heights, bulk band structures on the same energy scale, and the definition of effective midgap energies corresponding to charge neutrality for each bulk constituent.

Band Offsets in Semiconductor Heterojunctions

An expression for the potential set up by a swift ion when it crosses a solid-vacuum interface is presented. The evaluation of this expression is carried out by using the plasmon-pole approximation for the dielectric function.

Wake potential in the vicinity of a surface.

The question of band offsets and details of exciton binding are investigated in the CdTe/(Cd,Mn)Te heterostructure in the quantum-well limit. Photoluminescence excitation spectroscopy in external magnetic fields is used to vary the quantum-well potential depths in this moderately strained (0.6% lattice mismatch) diluted magnetic semiconductor heterostructure. Large Zeeman splittings are observed at all the principal quantum-well transitions and at the barrier band gap for a structure of CdTe well thicknesses of 50 A\r{} and a Mn-ion concentration in the barrier layer of x=0.24. A variational theory is developed for excitons, especially accounting for the possibility of a small valence-band offset. Good agreement between theory and experiment is obtained and a band offset of 25 meV is deduced for the heavy-hole valence band, corresponding to a conduction- to valence-band offset ratio of about 14:1. This implies that the valence-band offset in a hypothetical strain-free case is virtually zero. The accuracy of the offset determination is believed to be better than 10 meV. Exciton binding energies are found to vary appreciably in the magnetic field; the zero-field value is approximately twice that for bulk CdTe.

Band offsets and excitons in CdTe/(Cd,Mn)Te quantum wells.

Application of moderate electric fields to ZnSe/(Zn,Mn)Se quantum wells yields distinct spectral shifts of the recombining exciton luminescence. This shows that confinement effects in this heterostructure are sufficient to increase the exciton ionization threshold. At high applied fields and low temperatures, injection of hot electrons from the n+GaAs/ZnSe heterojunction at our substrate/buffer layer excites yellow luminescence from internal transitions of the Mn ion in (Zn,Mn)Se layers.

Electric field induced shifts in exciton luminescence in ZnSe/(Zn,Mn)Se superlattices

A numerical calculation is presented of a quantum-mechanical model of an electron leaving a metal under the pull of an electric field. The calculation includes possible interference phenomena from the electron virtual emission of a surface plasmon. The emitted current is calculated as a function of electric field.

Dynamic image potentials and field emission

The transport equation is solved for a quantum-mechanical system in a transverse magnetic field The solution gives the linear transport coefficients for electrostatic fields and temperature gradients for electrons in metals In term of a small expansion parameter, the solution to lowest order confirms the existing semiclassical theory on electrical conductivity and thermal conductivity We also found that the electron-phonon mass enhancement factor is present in the adiabatic thermopower The next-higher-order approximation exhibits the anisotropic effect caused by the presence of magnetic fields and explains the experimentally observed linear magnetoresistance in simple metals under a high magnetic field

J. W. Wu

Papers

Band offsets and excitons in CdTe/(Cd,Mn)Te quantum wells.

Electric field induced shifts in exciton luminescence in ZnSe/(Zn,Mn)Se superlattices

Dynamic image potentials and field emission

Transverse magnetoresistance and thermopower in metals