From Understanding Lasers


Semiconductor physics as a whole is beyond the scope of this book, but some fundamental aspects of semiconductors are crucial to the understanding of semiconductor lasers. This section will cover those aspects and semiconductor materials, before we get into the details of light emission and lasers.

9.2.1 Valence and Conduction Bands

Semiconductors get their name because they conduct electricity better than an insulator but not as well as a conductor. This arises from the nature of the bonds between atoms and their electrons in the solid. In an insulator like glass, the outer electrons are tightly bound to atoms, often in covalent bonds between pairs of atoms. In conductors like copper, the outer electrons are only loosely bound to atoms, so they can flow freely though the material if a voltage is applied across it. A semiconductor falls in between the two.

The difference can be explained by considering electrons to be in one of two levels: a valence band in which they are bound to atoms, and a conduction band in which they are free to move around in the solid. The valence band is at a higher energy level than the conduction band, but in...

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Semiconducting Materials
Semiconductors (metalloids) or semiconductor materials are used to fabricate microelectronic and optoelectronic devices such as transistors, photodetectors or solar cells.
Radiation Detectors
Radiation detectors are used for medical diagnoses, radioactive dating measurements, and measurements of background radiation, activity levels and radiation doses.
Schottky Diodes
Schottky diodes in their simplest form consist of a metal layer that contacts a semiconductor element. The metal / semiconductor junctions exhibit rectifying behavior (i.e., the current passes through the structure more readily with one polarity than the other).
Diodes are electronic components that conduct electric current in only one direction, functioning as a one-way valve. Diodes are manufactured using semiconductor materials such as silicon, germanium or selenium and are used as voltage regulators, signal rectifiers, oscillators and signal modulators / demodulators.
Photovoltaic Cells and Panels
Photovoltaic cells or solar cells generate a voltage when radiant energy falls on the boundary between dissimilar substances. A solar panel, also called a photovoltaic panel, is a group of photovoltaic cells that are enclosed to keep the cells safe and so that the voltage obtained from each cell can be combined.

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