Introduction

This chapter deals with several topics. There is considerable interest in fabricating quasi-2D structures in which the electron–phonon interaction is reduced. Optical-phonon engineering is in its infancy, but already there have been investigations of the effect of incorporating monolayers and conducting layers. One of the first quasi-2D systems to be studied was the thin ionic slab, yet there are still problems connected with the description of optical modes in such structures. The increasing sophistication of microfabrication techniques has led to the creation of quasi-one-dimensional (quantum wires) and quasi-zero-dimensional (quantum dots) structures that are expected to have interesting physical properties. It is important to establish the mode structure, both electron and vibrational, in these systems. In this chapter we consider some of these topics briefly.

Monolayers

The study of short-period superlattices in electronic and optical devices has received considerable attention and there are several reasons why this has been so. Ease of growth and reduction of interface roughness and residual impurities make for more perfect structures. Replacing random alloys, such as AlxGa1 – x As, with their ordered superlattice counterparts (GaAs)m/(AlAs)n eliminates alloy scattering. In the AlxGa1–x As system there is the added advantage of avoiding the troublesome DX center. The replacement of random alloys by equivalent superlattices in bandgap engineering is unproblematic.