They are often called "quantum crystallites", "quantum dots" or "quasi-zero-dimensional structures".
As the size of these crystallites ranges from one to tens nanometers, the word "nanocrystals" is widely used as well. This term refers to the crystallites size only, whereas the other terms contain a certain hint at the interpretation of their electron properties in terms of the quantum confinement effects.
From the standpoint of a solid state physicist, nanocrystals are nothing else but a kind of a low-dimensional structure complementary to quantum wells two-dimensional structures and quantum wires one-dimensional structures.
However, the finiteness of quasi-zero-dimensional species results in a number of specific features that are not inherent in the two- and one-dimensional structures. Quantum wells and quantum wires still possess a translational symmetry in two or one dimensions, and a statistically large number of electronic excitations can be created. In nanocrystals, the translational symmetry is totally broken and only a finite number of electrons and holes can be created within the same nanocrystal.
Therefore, the concepts of the electron-hole gas and quasi-momentum fail in nanocrystals. Additionally, a finite number of atoms in nanocrystals promotes a variety of photoinduced phenomena like persistent and permanent photophysical and photochemical phenomena that are known in atomic and molecular physics but do not occur in solids.
Semiconductor Optics 1
Finally, nanocrystals are fabricated by means of techniques borrowed from the glass technology, colloidal chemistry, and other fields that have nothing common with the crystal growth. From the viewpoint of molecular physics, nanocrystals can be considered as a kind of large molecules. Similar to molecular ensembles, nanocrystals dispersed in a transparent host environment liquid or solid exhibit a variety of guest-host phenomena known for molecular structures.
Moreover, every nanocrystal ensemble has inhomogeneously broadened absorption and emission spectra due to distribution of sizes, defect concentration, shape fluctuations, environmental inhomogeneities, and other features.
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Therefore, the most efficient way to examine the properties of a single nanocrystal which are smeared by the inhomogeneous broadening is to use numerous selective techniques developed in molecular and atomic spectroscopy. Additionally, as the size of crystallites and their concentration grow, the heterogeneous medium "matrix-crystallites" becomes a subject of the optics of ultradisperse media, thus introducing additional aspects to the optical properties of nanocrystal ensembles.
Because of the above-mentioned features, studies of the optical properties of nanocrystals form a new field bordering solid state physics, optics, molecular physics, and chemistry. Despite matrices colored with semiconductor nanocrystals are known in the human practice for a number of centuries as stained-glasses, the systematic studies of their physical properties have begun not long ago.
Probably, first investigations on quasi-zero-dimensional structures were the pioneering works by Froelich and Kubo in which non-trivial properties of small metal particles were predicted due to a discreteness of electron spectra. The systematic studies of size-dependent optical properties of semiconductor nanocrystals have been stimulated by impressive advances in the quantum confinement approach for fine semiconductor layers quantum wells and needle-like structures quantum wires.
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The St. Since then, a great progress in the field has been achieved due to extensive studies performed by thousands of researchers over the world. The advances in the theory of semiconductor quantum dots have been described thoroughly in the nice book by Banyai and Koch The present book is aimed to summarize the progress in experimental studies of semiconductor nanocrystals.
Semiconductor microcavity polaritons - IOPscience
Chapters I-IV contain a brief description of the theoretical results on electron states in an idealized nanocrystal, a sketch of the growth techniques and structural properties, and a survey of the selective optical techniques and relevant optical effects known for other spectrally inhomogeneous media. These Chapters are designed to provide an introductory overview which seems to be reasonable taking into account an interdisciplinary nature of the field.
Pages Transport Phenomena in Heavily Doped Semiconductors. Optical Properties of Heavily Doped Semiconductors. Behavior of Impurities in Heavily Doped Semiconductors.
Preparation of Heavily Doped Semiconductors. Some Applications of Heavily Doped Semiconductors. Back Matter Pages About this book Introduction Recently, there has been a considerable upsurge of interest in heavily doped semiconductors. This interest is due primarily to the expanding range of applications of such. The rapid growth in the number of papers on heavily doped semiconductors makes it difficult to review the results obtained so far.
Nevertheless, the author hopes that, in spite of this, the book will be useful.