This term is a popular shortening of polycrystalline silicon
. Polysilicon consists of many grains of crystalline
silicon with abrupt discontinuities between grains. Because polysilicon does not have perfect crystalline structure, it is more electrically resistive
than crystalline Si
Highly-doped polysilicon is used as the MOSFET gate in modern integrated circuits. While polysilicon is an inferior gate material to metal--it is more resistive and suffers from the "depletion effect" which decreases the gate's control of the channel--it has the advantage that it can withstand subsequent high-temperature processing.
Polysilicon is easily deposited by chemical vapor deposition (CVD). The resistance of polysilicon in integrated circuits is usually greatly reduced by the formation of a metal silicide on top. These silicides can withstand high-temperature steps such as dopant annealing. Unfortunately, the depletion effect persists after silicidation.