Quantum dots: Genesis, the excitonic zoo, and nanodevices

Universal self-organization and self-ordering effects at surfaces of semiconductors lead to the formation of coherent zero-dimensional clusters called quantum dots (QDs). The electronic and optical properties of QDs, being smaller than the de-Broglie-wavelength in all three directions of space are closer to those of atoms in a dielectric cage than of solids. Their delta-function-like energy eigenstates are only twofold (spin) degenerate. All few particle excitonic states are strongly Coulomb correlated. Their energies depend on shape and size of the dots, such that positive or negative biexciton binding energies or fine-structure splitting caused by exchange interaction appear.

Consequently, single QDs present the most practical possible basis of emitters of single polarized photons (Q-bit emitters) on demand or entangled photons via the biexciton-exciton cascade for future quantum cryptography and communication systems. Multiple QD layers, as active materials, are extremely promising for novel optoelectronic devices, like edge and surface emitting lasers, amplifiers with properties going far beyond devices based on higher dimensional systems. Semiconductor nanotechnologies transform presently to enabling technologies for new economies. It is expected that first commercialization of nanophotonic devices and systems will appear soon. High bit rate and secure quantum cryptographic systems, nano-flash memories, or ultra-high speed nanophotonic devices for future optical interconnects, the Terabus, and 100 - 160 Gbit/s Ethernet present some of the first fields of applications of quantum dot devices.