115A_1_EE115A_W10-Chap2

115A_1_EE115A_W10-Ch - Chapter 2 Basic Physics of Semiconductors h 2.1 Semiconductor materials and their properties 11 h 2.2 PN-junction diodes h

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Unformatted text preview: Chapter 2 Basic Physics of Semiconductors h 2.1 Semiconductor materials and their properties 11 h 2.2 PN-junction diodes h 2.3 Reverse Breakdown Semiconductor Physics CH2 Basic Physics of Semiconductors 12 h Semiconductor devices serve as heart of microelectronics. h PN junction is the most fundamental semiconductor device. Charge Carriers in Semiconductor CH2 Basic Physics of Semiconductors 13 h To understand PN junction’s IV characteristics, it is important to understand charge carriers’ behavior in solids, how to modify carrier densities, and different mechanisms of charge flow. Periodic Table CH2 Basic Physics of Semiconductors 14 h This abridged table contains elements with three to five valence electrons, with Si being the most important. Silicon CH2 Basic Physics of Semiconductors 15 h Si has four valence electrons. Therefore, it can form covalent bonds with four of its neighbors. h When temperature goes up, electrons in the covalent bond can become free. Electron-Hole Pair Interaction CH2 Basic Physics of Semiconductors 16 h With free electrons breaking off covalent bonds, holes are generated. h Holes can be filled by absorbing other free electrons, so effectively there is a flow of charge carriers. Free Electron Density at a Given Temperature 3 15 3 10 3 2 / 3 15 4 00 / 10 08 . 1 ) 300 ( / 2 exp 10 2 . 5 ectrons cm electrons K T n cm electrons kT E T n i g i × = =- × = CH2 Basic Physics of Semiconductors 17 h E g , or bandgap energy determines how much effort is needed to break off an electron from its covalent bond. h There exists an exponential relationship between the free- electron density and bandgap energy. / 10 54 . 1 ) 600 ( cm electrons K T n i × = = Doping (N type) CH2 Basic Physics of Semiconductors 18 h Pure Si can be doped with other elements to change its electrical properties. h For example, if Si is doped with P (phosphorous), then it has more electrons, or becomes type N (electron). Doping (P type) CH2 Basic Physics of Semiconductors 19 h If Si is doped with B (boron), then it has more holes, or becomes type P. Summary of Charge Carriers CH2 Basic Physics of Semiconductors 20 Electron and Hole Densities 2 i n np = A i A N n n N p 2 ≈ ≈ Majority Carriers : Minority Carriers : ajority Carriers : CH2 Basic Physics of Semiconductors 21 h The product of electron and hole densities is ALWAYS equal to the square of intrinsic electron density regardless of doping levels....
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This note was uploaded on 01/08/2011 for the course EE 115 taught by Professor Kaiser during the Spring '09 term at UCLA.

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115A_1_EE115A_W10-Ch - Chapter 2 Basic Physics of Semiconductors h 2.1 Semiconductor materials and their properties 11 h 2.2 PN-junction diodes h

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