Single-crystal devices

The great energy consumption, limited recources of traditional fuels and environmental problems have lead to intensive research on the conversion of solar energy during the last fifteen years. Conversion into electrical energy has been realized in technical devices consisting of pn-junction photovoltaic cells. Efficiencies of up to 20 % have been obtained with single crystal devices and around 9 % with polycrystalline or amorphous layers. 

Prominent features of these single crystal devices are [102] ... 

A useful avalanche diode that works in either direction is the "varistor," sometimes called the "metal oxide varistor," or "MOV." It is not just a single crystal device as the previously described semiconductors are, but instead it is polycrystalline ceramic material, usually zinc oxide, with many small PN junctions at the grain boundaries. It is quite inexpensive and is very rugged, so it can be found as an important part inside most "surge protector power strips" for connecting multiple computer modems, printers, etc., to protect them against inductive kicks and even most "spikes" ("transients") from lightning. ... 

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