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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
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
1018 xn xp
16 10 x (cm) e) Sketch the electric field vs. position across the depletion region.
(V/cm) xn xp x (cm) f) Sketch the electrostatic potential vs. position across the depletion region.
Potential (V) xn xp x (cm) g) Sketch the band-diagram; be sure to include the Fermi levels.
Energy (eV) EF
Ev xn xp x (cm) 2) In a certain piece of semiconductor, the electron concentration can be found according to the
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
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 C 0.02586 V 1000
V.s 2 10
0.207 2 i. e. in the negative x direction .
0.207 2 0.801 2
0.594 2 in the positive x‐direction.
1.602 , cm‐3 mA
i.e. in the positive x‐direction .
10 , 1– 2 10 cm‐4 1000 V
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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.
- Spring '07