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cont s boron has 3 electrons in its outer boron shell

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Unformatted text preview: orus becomes phosphorus positive ion after giving up electron electron Improving Conduction by Doping (cont.) (cont.) s Boron has 3 electrons in its outer Boron shell, so it contributes a hole if it displaces a silicon atom displaces – boron is an acceptor dopant boron acceptor – yields p type silicon yields silicon – boron becomes negative ion boron after accepting an electron after Epitaxial Growth of Silicon Silicon s Epitaxy grows silicon on top of existing silicon existing s Silicon is placed in chamber at Silicon high temperature high Appropriate gases are fed into Appropriate the chamber the Can grow n type, then switch to Can p type very quickly type – uses chemical vapor uses deposition deposition – new silicon has same new crystal structure as original original – 1200 o C (2150 o F) 1200 s – other gases add other impurities to the mix impurities s Diffusion of Dopants Diffusion s It is also possible to introduce It dopants into silicon by heating them so they diffuse into the diffuse silicon silicon Can be done with constant Can concentration in atmosphere concentration top – no new silicon is added – high heat causes diffusion – close to straight line close concentration gradient concentration – predeposition – bell-shaped gradient s s Or with constant number of atoms Or per unit area per Diffusion causes spreading of Diffusion doped areas doped side s Diffusion of Dopants (continued) Diffusion Concentration of dopant in surrounding at...
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