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ECE 410, Prof. A. MasonLecture Notes 6.1Intrinsic 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 intrinsiccharge carriers–electron-hole pairs are created by thermal energy–intrinsic carrier concentration≡ni= 1.45x1010cm-3, at room temp.–function of temperature: increase or decrease with temp?–n = p = ni, in intrinsic (undoped) material• n ≡number of electrons, p ≡number of holes–mass-action law, np = ni2•applies to undoped and doped material
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ECE 410, Prof. A. MasonLecture Notes 6.2Extrinsic Silicon Properties•doping, adding dopantsto modify material properties– n-type = n+, add elements with extra an electron•(arsenic, As, or phosphorus, P), Group V elements• nn≡concentration of electrons in n-type material• nn= Ndcm-3, Nd≡concentration of donoratoms• pn≡concentration of holes in n-type material• Ndpn= ni2, 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)• pp≡concentration of holes in p-type material• pp= Nacm-3, Na≡concentration of acceptoratoms• np≡concentration of electrons in p-type material• Nanp= ni2, using mass-action law– always a lot more p than n in p-type material– if both Ndand Napresent, nn= Nd-Na, pp=Na-Nddo example on boardni2= 2.1x1020n+/p+ defines regionas heavily doped, typically ≈1016-1018cm-3less highly doped regions generally labeled n/p (without the +)PP++-group Velementionelectronn-type DonorfreecarrierBB++-group IIIelementholep-type Acceptorionfreecarrier