3-Handouts_Handout_2a - Silicon Crystal and Doping...

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Silicon Crystal and Doping P Si Si Si Si Si Donated valence electron that is unbound within the Si lattice e - An overall positive charge is present due to the unbalanced proton of the P atom Intrinsinic Silicon n doped Silicon p doped Silicon
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Intrinsic Silicon The electrons and holes have two mechanisms at temperatures greater than zero ° K namely: ¾ Thermal Ionization ¾ Recombination At thermal Equilibrium Generation Rate = Recombination Rate n = p = n i (intrinsic concentration) n i = 1.5*10 10 carriers/cm 3 at 300 ° K Si Atoms = 5*10 22 atoms/cm 3 Two-dimensional representation of the silicon crystal. The circles represent the inner core of silicon atoms, with +4 indicating its positive charge of +4q, which is neutralized by the charge of the four valence electrons. Observe how the covalent bonds are formed by sharing of the valence electrons. At 0 K, all bonds are intact and no free electrons are available for current conduction. At room temperature, some of the covalent bonds are broken by thermal ionization. Each broken bond gives rise to a free electron and a hole, both of which become available for current conduction.
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N-Doped Silicon ± Mobile Carrier Concentration ± n no N D ± n no p no = n i 2 ± p no n i 2 /N D ± Example: At 300 ° K and for N D = 10 17 cm -3 ± n no 10 17 cm -3 ± p no 2.25*10 3 cm -3 A silicon crystal doped by a pentavalent element. Each dopant atom donates a free electron and is thus called a donor. The doped semiconductor becomes n type
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This note was uploaded on 01/16/2010 for the course EE ee203 taught by Professor Electronics1 during the Spring '09 term at King Fahd University of Petroleum & Minerals.

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3-Handouts_Handout_2a - Silicon Crystal and Doping...

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