20111ee2_1_Practice Set 1_Solution

20111ee2_1_Practice Set 1_Solution - Physics for Electrical...

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Unformatted text preview: Physics for Electrical Engineers Prof. B. Jalali EE 2 Winter 2011 Practice Problem Set #1 Solutions 1) Consider a 1-dimensional pn-junction, with a p-side doping of 1016 cm-3 and n-side doping of 1018 cm-3. a) Calculate Vbi, the built-in voltage. . b) Calculate W, the depletion width (we call it xd in lecture). . c) Calculate xp and xn, which are the depletion widths in the p-side and n-side, respectively. . . d) Sketch the charge-block diagram (i.e. charge density vs. position) across the depletion region. ρ (q/cm3) 1018 xn xp 16 10 x (cm) e) Sketch the electric field vs. position across the depletion region. E-field (V/cm) xn xp x (cm) f) Sketch the electrostatic potential vs. position across the depletion region. Electrostatic Potential (V) xn xp x (cm) g) Sketch the band-diagram; be sure to include the Fermi levels. Ec Electron Potential Energy (eV) EF Ev xn xp x (cm) 2) In a certain piece of semiconductor, the electron concentration can be found according to the following formula: 1– 10 cm‐3 2µm is the width of the piece. There is also a uniform electric field equal to where cm2 V 1000 pointing in the positive x-direction. The electron mobility is 1000 . Find the cm V.s direction and magnitude of the electron drift current density, electron diffusion current density, and total current density at . (The system may or may not be in equilibrium). 1.602 , 0.801 10 C 1000 cm2 V.s cm‐4 cm2 10 10 C 0.02586 V 1000 V.s 2 10 mA 0.207 2 i. e. in the negative x direction . cm mA mA 0.207 2 0.801 2 , cm cm mA 0.594 2 in the positive x‐direction. cm 1.602 , cm‐3 mA i.e. in the positive x‐direction . cm2 10 , 1– 2 10 cm‐4 1000 V cm ...
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This note was uploaded on 10/07/2011 for the course EE 2 taught by Professor Vis during the Spring '07 term at UCLA.

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