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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 1dimensional pnjunction, with a pside doping of 1016 cm3 and nside doping of
1018 cm3.
a) Calculate Vbi, the builtin 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 pside and nside, respectively.
.
.
d) Sketch the chargeblock 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.
Efield
(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 banddiagram; 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 xdirection. 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.
 Spring '07
 Vis
 Volt

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