Ch6.pdf - Intrinsic Silicon Properties Read textbook...

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ECE 410, Prof. A. Mason Lecture Notes 6.1 Intrinsic Silicon Properties Read textbook, section 3.2.1, 3.2.2, 3.2.3 Intrinsic Semiconductors undoped (i.e., not n+ or p+) silicon has intrinsic charge carriers electron-hole pairs are created by thermal energy intrinsic carrier concentration n i = 1.45x10 10 cm -3 , at room temp. function of temperature: increase or decrease with temp? n = p = n i , in intrinsic (undoped) material • n number of electrons, p number of holes mass-action law , np = n i 2 applies to undoped and doped material
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ECE 410, Prof. A. Mason Lecture Notes 6.2 Extrinsic Silicon Properties •doping, adding dopants to modify material properties – n-type = n+, add elements with extra an electron (arsenic, As, or phosphorus, P), Group V elements • n n concentration of electrons in n-type material • n n = N d cm -3 , N d concentration of donor atoms • p n concentration of holes in n-type material • N d p n = n i 2 , using mass-action law – always a lot more n than p in n-type material – p-type = p+, add elements with an extra hole (boron, B) • p p concentration of holes in p-type material • p p = N a cm -3 , N a concentration of acceptor atoms • n p concentration of electrons in p-type material • N a n p = n i 2 , using mass-action law – always a lot more p than n in p-type material – if both N d and N a present, n n = N d -N a , p p =N a -N d do example on board n i 2 = 2.1x10 20 n+/p+ defines region as heavily doped, typically 10 16 -10 18 cm -3 less highly doped regions generally labeled n/p (without the +) P P + + - group V element ion electron n-type Donor free carrier B B + + - group III element hole p-type Acceptor ion free carrier
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