light-activated silicon controlled switch
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light-activated silicon controlled switch[′līt ¦ak·tə‚vād·əd ¦sil·ə·kən kən¦trōld ′swich]
A semiconductor device that has four layers of silicon alternately doped with acceptor and donor impurities, but with all four of the p and n layers made accessible by terminals; when a light beam hits the active light-sensitive surface, the photons generate electron-hole pairs that make the device turn on; removal of light does not reverse the phenomenon; the switch can be turned off only by removing or reversing its positive bias. Abbreviated LASCS.