Gallium-doped silicon

Cadmium iodide Octahedral site Gallium-doped silicon Sodium sulfide Perovskite Calcium fluoride Gallium arsenide Wurtzite and zinc blende Tin(IV) oxide... 

Explain how doping silicon with either phosphorus or gallium increases the electrical conductivity over that of pure silicon. 

A (a) Elements with two valence electrons, e.g.. Be, Sr, Cd, (b) elements with three valence electrons, e.g., B, Ga, In, (c) elements with six valence electrons, e.g., O, Se, Te. 25.5B Carbon can be combined with silicon to produce a semiconductor. Arsenic can be used to dope silicon to produce an -type semiconductor and gallium can be used to dope silicon to produce a p-type semiconductor. 

Hyperpure silicon can be doped with boron, gallium, phosphorus, or arsenic to produce silicon for use in transistors, solar cells, rectifiers, and other solid-state devices which are used extensively in the electronics and space-age industries. 

Fig. 10. Spreading resistance profiles for silicon doped with indium, gallium, and aluminum.

Elemental forms of gallium and arsenic, plus small quantities of dopant material — silicon, tellurium or chromium — are reacted at elevated temperatures to form ingots of doped single-crystal GaAs. 

When a silicon ciystal is doped with atoms of elements having a valence of less than four, e.g., boron or gallium (valence =3), only three of the four covalent bonds of the adjacent silicon atoms are occupied. The vacancy at an unoccupied covalent bond constitutes a hole. Dopants that contribute holes, which in turn act like positive charge earners, are acceptor dopants and the resulting crystal is p-type (positive) silicon. See Fig. 1(d). 

Explain why silicon doped with gallium has a higher electrical conductivity than pure silicon. 

Silicon (Si) Silicon is a lustrous silvery gray material. Because silicon conducts electricity, but not as well as a metal, silicon is classified as a semimetal. Crystals of pure silicon that have been doped with arsenic or gallium are known as semiconductors and are used to fabricate computer chips. Silicone rubbers are polymers containing silicon, oxygen, and various hydrocarbon groups, and are used in applications ranging from sealants to breast implants. 

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