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Unformatted text preview: Lecture 18, Slide 1 EECS40, Fall 2003 Prof. King Lecture #18 OUTLINE – Generation and recombination – Charge-carrier transport in silicon – Resistivity as a function of doping Reference Texts on reserve in Engr. Library • Howe & Sodini Chapter 2.1 : Pure semiconductors Chapter 2.2 : Generation, recombination, thermal equilibrium Chapter 2.3 : Doping Chapter 2.4 : Carrier Transport Chapter 2.6 : IC Resistors • Schwarz and Oldham Chapter 13 : Semiconductor Devices Lecture 18, Slide 2 EECS40, Fall 2003 Prof. King Generation • We have seen that conduction (mobile) electrons and holes can be created in pure (intrinsic) silicon by thermal generation . – Thermal generation rate increases exponentially with temperature T • Another type of generation process which can occur is optical generation – The energy absorbed from a photon frees an electron from covalent bond • In Si, the minimum energy required is 1.1eV , which corresponds to ~1 µ m wavelength (infrared region) • Note that conduction electrons and holes are continuously generated, if T > 0 Lecture 18, Slide 3 EECS40, Fall 2003 Prof. King Recombination • When a conduction electron and hole meet, each one is eliminated. The energy lost by the conduction electron (when it “falls” back into the covalent bond) can be released in 2 ways: 1. to the semiconductor lattice (vibrations) “thermal recombination” Æ semiconductor is heated 2. to photon emission “optical recombination” Æ light is emitted • Optical recombination is negligible in Si. Optical recombination is negligible in Si....
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- Fall '08