Solids can be categorised into conductors, semiconductors or ____ by their ____ and their ability to ____ electricity. Every ____ has its own characteristic energy band structure. For a solid to be conductive, both ____s and accessible ____ states must be available.  The ____ in atoms are contained in energy ____. When the atoms come together to form ____, the electrons then become contained in energy bands separated by gaps. For ____, we have the situation where one or more bands are partially filled. Some metals have free ____ and partially filled valence bands, therefore they are highly conductive. Some metals have overlapping ____ and conduction bands. Each band is partially filled and therefore they are ____.  In an ____, the highest occupied band (called the valence band) is full. The first unfilled band above the valence band is the ____ band. For an insulator, the gap between the valence band and the conduction band is ____ and at room temperature there is not enough ____ available to move electrons from the valence band into the conduction band where they would be able to contribute to conduction. There is no ____ conduction in an insulator.  In a ____, the ____ between the valence band and conduction band is smaller and at ____ there is sufficient ____ available to move some electrons from the valence band into the conduction band allowing some conduction to take place. An ____ in temperature increases the conductivity of a semiconductor  During manufacture, semiconductor may be ____ with specific impurities to increase their conductivity, resulting in two types of semiconductor, ____-type and n-type. When a ____ contains the two types of doping in adjacent layers, a p-n junction is formed. There is an electric field in the p-n junction. The electrical properties of this p-n junction are used in a number of devices.  Diodes can be ____ biased or reverse biased. Forward bias reduced the electric field, reverse bias increases the electric field. LEDS are forward biased p-n ____ diodes that emit ____. The forward bias potential difference across the junction causes electrons to move from the conduction band of the n - type semiconductor towards the conduction band of the p-type semiconductor. Photons are emitted when electrons 'fall' from the conduction band into the ____ band either side of the junction.  solar cells are p-n junctions designed so that a potential difference isproduced when ____ are absorbed. (This is known as the photovoltaic effect.) The absorption of photons provides energy to ‘raise’ electrons from the valence band of the ____ to the conduction band. The p-n junction causes the electrons in the conduction band to move ____ the n-type semiconductor and a ____ is produced across the solar cell.

Semiconductors and p-n junctions

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