Worldwide, many researchers are fascinated from the rich physics of se- conductor quantum dots (QDs) and their high potential for applications in photonics and quantum information technology. QDs are nanometer-sized three-dimensional structures which con?ne electrons and holes in dimensions oftheircorrespondingDeBrogliewavelength.Asaresult,theenergylevelsare quantized and for that reason they are also often referred as arti?cial atoms. Epitaxially grown QDs which are the subject of this book are embedded in a solid state semiconductor matrix and their size, shape, composition, and lo- tion can be tailored to a large extent by modern growth techniques. In QDs, excitations can involve more than a single carrier and interaction among the carriers modify or even dominate the emission properties. Therefore, a simple two-level description is only appropriate under certain well de?ned expe- mental conditions. Tremendous progress has been obtained in understanding their electronic, optical and spin properties mainly by performing single dot spectroscopy and using appropriate theoretical models.
