(c) Dr Paul Kinsler. [Acknowledgements & Feedback]
This is part of an information maze -- see the index-file for the full picture.
Semiconductors are materials that nearly conduct electricity, and lie between conductors and insulators. Semiconductors are useful because by changing their environment or composition we can make them either conduct electricity, or not conduct electricity. In addition, they interact significantly with light. Because of this control we can design semiconductor devices that have a variety of useful properties -- amplifying or detecting electrical current, as well as detecting, amplifying, or emitting light.
If we continue with the "set of shelves" analogy used in the description of solids, semiconductors are materials where the highest occupied shelf is completely full of electrons, but where the next shelf up is close by. Although there is no space for the electrons to move around on the shelf, it is not too hard for an electron to gain the extra energy require to leap up into the nearby higher shelf, where it can move freely, and so carry an electric current. This leaves a gap, or "hole" in the lower shelf, which can also move. Since we can easily supply the extra energy from outside or by clever design, we can control the way the semiconductor conducts electric current.
Electric current is carried by both electrons and "holes" in semiconductors. These electric-charge carriers move differently through semiconductors with different compositions, so we can make different sorts of semiconductor-structures.
Because electrons and holes have opposite electric-charges, they can attract each other and form excitons.
These carriers (and excitons) do not move freely through the semiconductor. The crystal lattice of atoms does affect their motion by making them more likely to travel at certain speeds, but a perfect crystal will not cause them to be deflected. However, their motion is affected by imperfections in the lattice, as well as by phonons.
XINDEX: solid, semiconductor-structure, semiconductor-structure, quantum-wire, quantum-well, quantum-dot, quantum-computer, optical-cavity, insulator, index-file, exciton, conductor, index-file.
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XKEYWORD: semiconductor
Email Feedback: Dr.Paul.Kinsler@physics.org
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