The formation mechanisms, structure and optoelectronic properties of Ga(In)As/(Al)GaAs quantum dot (QD) heterostructures grown by organometallic chemical vapor deposition on patterned (111)B GaAs substrates are reviewed. With this approach, it is possible to prepare high-quality semiconductor QDs whose position on a substrate is precisely controlled via a pre-growth photolithography step. The dots are formed at the center of an inverted, tetrahedral pyramid and are surrounded by distinct, low-dimensional barriers (quantum wires and quantum wells). Reproducible neutral and charged exciton states are observed in the QDs and are probed using microphotoluminescence and photon correlation spectroscopy. Single- and correlated-photon emissions are systematically detected from specific single and biexciton states. The emission spectra of light emitting diodes incorporating single pyramidal dots indicate the possibility of preferential injection of charge carriers via self-ordered wires connected to the dots. Finally, photonic crystal structures incorporating pyramidal QDs with controlled energy states are demonstrated. (C) 2004 Elsevier B.V. All rights reserved.