Quantum Dot Arrays: Electromagnetic Properties
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A fundamental breakthrough in semiconductor device physics is connected with the recent progress in the synthesis of sheets of nanoscale narrow-gap insertions in a host semiconductor—quantum dots (QDs). The key peculiarity of QDs is related to the spatial confinement of charge carriers and their discrete energy levels determined by QD size and shape. The shape is dictated by the growth kinetics and the parameters of the materials governing the thermodynamics of growth. The large body of recent results on the physical properties of QDs and their utilization for the QD laser design has been discussed in Ref. .
Apart from charge carrier confinement, there exists a class of effects governed by the intrinsic spatial inhomogeneity of the QD heterostructures. Transparent and dissipative heterogeneous media with small inclusions of one material into another material, conventionally referred to as composite materials, exhibit, in general, new mechanical, electronic, as well as optical properties, which are not inherent to each individual component. In the case of QD heterostructures, a conventional picture is modified because of specific properties of excitons, coupled electron–hole states, which define the QD response. First, excitonic composite is constituted by resonant particles and, consequently, is characterized by resonant response; moreover, inverse population is possible owing to the discrete energy spectrum of excitons. Thus a QD-based composite is a resonant active system. Another specific property of QD composites appears owing to the quantum nature of excitons: the exciton Bohr radius aB can either exceed the QD linear extension (strong confinement regime), or be much less (weak confinement regime). In the latter case, often realized in experiments, the QD electromagnetic response becomes nonlocal (i.e., constitutive relations for polarization of the QD medium take the form of integral operators). Electromagnetic properties of QD-based composites are the focus of the present paper. Consideration is based on earlier published articles of various authors.