Quantum wires and dots are unique condensed matter systems where electron and hole localisation can be achieved by lateral confinement down to quasi 0-dimensions. Here we review how these nanostructures are realised and their optical properties, mainly from an experimental point of view. We discuss changes in the energy and momentum relaxation mechanisms as the lateral dimensions are reduced, such as the so-called phonon "bottleneck", using the example of GaAs-GaA1As quantum dots and wires. Examples of strain-relief by deep etching in both, nominally lattice-matched and strained materials are given. The emission of hot luminescence or resonant Raman scattering from dots and wires is shown to be a finger print of exciton localization. Many-body effects are shown to be important in nanostructures such as GaAs-GaAlAs and Si-SiGe dots and wires. The emergence of ultra-thin submonolayer quantum wells has provided further insights into the role of exciton localization in nanostructures and we discuss here the case of submonolayers of InAs embedded in a GaAs matrix.Considerations for devices are discussed along with future trends in the field.

We present experimental and theoretical results on the low temperature luminescence intensity of dry etched GaAs-AlGai..As quantum dots. The luminescence intensity was found to decrease by two orders of magnitude with the decrease of dot sizes from 1im to 6Onm. Our intrinsic model of the emission yield invokes slower momentum and energy relaxation mechanisms as the lateral dimensions decrease. The extrinsic effect, which we include in our interpretation of the luminescence intensity, involves carrier diffusion with a surface nonradiative recombination velocity. The combined effect (intrinsic and extrinsic) gives a very good fit to our data. The surface recombination velocity needed for the fit was 1O5cm/s. Raman studies on the quantum dots showed enhanced surface phonons with the decrease of the nanostructure sizes. "GaAs"-like and "A1As"-like surface phonons were also observed for the first time in etched nanostructures, in good agreement with the theoretical predications.

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