It has recently been shown that quantum dots based on the lead-salt semiconductor system (PbSe on PbEuTe) exhibit a three-dimensional ordering so that the dots arrange themselves in a face-centred cubic array, by Prof. G. Bauer’s group at Linz [G Springholtz et al, Science vol 282, p 734, 1998]. The ordered dot arrays display very high homogeneity in size. So far, there have been no systematic optical studies of these dots.
The subject of "photonic"
materials is very similar to X-ray scattering by crystals. It is possible
to show that arrays of blobs of material with differing refractive index
can set up Bragg scattering in such a way that certain wavelengths of light
cannot propagate through the array in any direction, just like the bandgap
of a semiconductor. Special defects can be introduced to mimic semiconductor
dopants so light can propagate only at a single frequency and in a specific
direction. These effects have been demonstrated in the microwave region
of the spectrum using mm-scale balls of polystyrene etc etc. This has enormous
numbers of technological applications for optoelectronics, if the devices
can actually be scaled down in size to optical wavelengths. So far most
optical photonic structures are only 2-dimensional. We would like to investigate
the possibility of using the self-organised dot material, whose nearest
neighbour dot-dot distance is in the optical wavelength regime, as a photonic
material.