Characteristics and structure of silicon using a neat labelled diagram.
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Answer:
A trivalent element such as boron, gallium or aluminiom has three valence electrons. Silicon and germanium are tetravalent elements.
A p-type semiconductor is formed when crystal of tetravalent sillicon or germanium is doped with a trivalent impurity.
(2)All the three valence electrons of an impurity atom form covali bonds with three of the four nearest-neighbour ost anoms. One bonds remains incomplete and needs an additional electron.
(3) A valence electron of a meighbouring atom may become free and electrons to the condaction band. Such mpurity holes greatly inrease the small concentration of holes that are already present in the material due thermal energy. The total hole concentration in the valence band (nh) greatly exceeds that of thermal electrons in the conduction band (ne) : (nh>>ne). Conduction in such an extrinsic semiconductor is largely due to holes.
(4) Such an extrinsic semiconductor is, therefore, termed positive charge carrier types, or p-type, semiconductor.
