Improved dot producers seek partners
The research group is looking for license agreements on the technology that is at the experimental development stage on a laboratory prototype. Patents have been applied for but not yet granted.
The method involves an interruption step after a layer of coherent QDs has been overgrown. Further an annealing process removes voids, desorbs interstitial atoms and grows out dislocation lines. Thermal treatment during the growth interruption raises the temperature above that optimal for QD formation stimulating the healing process and inducing evaporation of dislocation clusters.
Further, redistribution of the cover layer material smoothes the surface, making it possible to deposit an additional layer of QDs directly on the cover layer. This increases the possible QD densities. Common QD production methods often result in corrugated layers, which results in a large number of dislocations being formed at the expense of the QD density. Smoothing of the growth front also reduces losses when used with wave-guide structures.
Common methods for epitaxial growth of QD components include the Stranski-Krastanov growth mode in a molecular beam epitaxy (MBE) tool. The dots are formed spontaneously in a layer of material (self-assembly). This often generates lattice defects. Due to different optima for the QDs and the covering layer, the deposition of all epitaxial layer materials at their respective optimal temperatures is impossible.
Growth temperatures off the optimum cause lattice dislocations, dot defects or unsuitable inclusion potentials. This can create charge carriers that promote non-radiant recombination processes, resulting in low efficiency or even failure of the component. Moreover the formation process of the QDs can itself create defects. Due to kinetic effects or excessive strain energy, the material may dissipate the strain by forming individual or even clusters of dislocations.
Contact heike.hanspach@berlin.ihk.de
