Example 1: Equilibrium PN-Junction
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Transcript of Example 1: Equilibrium PN-Junction
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Example 1: Equilibrium PN-Junction
Problem Statement:A pn-diode has NA=ND=1016 cm-3 doping and a length of 1 um of both p and n-regions. Calculate analytically and verify via simulations the values of the:
(a) Built-in voltage Vbi
(b) Total depletion region width W.(c) Maximum electrical field at the metallurgical junction.
Analytically, the built-in voltageis calculated using:
2ln 0.714A D
bi Ti
N NV V V
n
One can also extract the built-in voltage from the energyband diagram using:
10.714bi Cp CnV E E V
q
Vbi
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Example 1: Charge Density
Question1: What is the analytical value of the total depletion region width?Answer1: The analytical value of the depletion region width is 0.432 um.
Question2: What is the extracted simulated value of the total depletion region width?Answer2: The simulated value of the depletion region width is ~ 0.43 um.
W
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Example 1: Electric Field Profile
Question1: What is the analytical value of the peak electric field?Answer1: The analytical value of the peak electric field is 33.14 kV/cm.
Question2: What is the extracted simulated value of the peak electric field?Answer2: The simulated value of the peak electric field is 32 kV/cm.
Emax
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Example 2: PN-Junction Under Bias
Problem Statement:A pn-diode has NA=ND=1016 cm-3 doping and a length of 1 um of both p and n-regions. Simulate:
(a) Energy band profile under applied bias VA=0.6 V(b) quasi-Fermi level variation with position(c) electric field under bias(d) forward IV-characteristic of the diode
The net built-in voltage is:Vbi - VA = 0.714 -0.6 = 0.114 V
The value extracted from thegraph for the net built-involtage is 0.115 V.
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Example 2: Quasi-Fermi Level Variation
Question: Where is the variation of the quasi-Fermi levels significant?
Answer: The variation of the quasi-Fermi levels is significant in regions in which the carrier concentration changes by orders of magnitude.
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Example 2: Electric Field Under Bias
Question1: Compare the equilibrium and non-equilibrium values of the field!Answer1: The peak non-equilibrium field is lower.
Question2: Compare the equilibrium and nonequilibrium depletion region widths!Answer2: The non-equilibrium depletion region with is smaller under forward bias.
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Example 2: Current Density
Question: How does the current vary with increasing the doping density of eitherthe p- or n-region, or both?Answer: With increasing the doping density of either the p-side, or the n-side, or both, the potential barrier for the minority carriers increases and the currentdecreases.
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Example 3: Non-Symmetric Junction
Problem Statement:A pn-diode has NA=1016 cm-3 and ND=1018 cm-3 doping, and a length of 1 um of both p and n-regions. Simulate:
(a) equilibrium energy band profile(b) charge density, to see the extent of the depletion regions(c) electric field profile to examine the contribution of the inversion charge
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Example 3: Charge Density
Question1: What is the analytical value of the total depletion region width?Answer1: The analytical value of the depletion region width is 0.327 um.
Question2: What is the extracted simulated value of the total depletion region width?Answer2: The extracted simulated value of the depletion region width is ~ 0.31 um.
W
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Example 3: Electric Field Profile
Question1: What is the analytical value of the peak electric field?Answer1: The analytical value of the peak electric field is 50.2 kV/cm.
Question2: What is the extracted simulated value of the peak electric field?Answer2: The simulated value of the peak electric field is 67.1 kV/cm.
InversionchargeDepletioncharge
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Example 4: Series Resistance
Problem statement:
In this exercise we will examine the series resistance effects under high bias conditions. The p-side doping is NA=1016 cm-3 and the n-side doping is ND=1016 cm-3. The length of the p-side and the n-side region is taken to be 1 um. Plot the following variables:
(a) Conduction band, valence band and the intrinsic level variation vs. position for applied bias VANODE=1.2 V.
(b) Quasi-Fermi level variation.
(c) Forward IV-characteristics of a diode for applied bias between 0 and 1.2 V in 0.05 V increments. From the forward IV-characteris- tics under high bias conditions extract the series resistance.
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Example 4: Energy Band
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Example 4: Quasi-Fermi Level
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Example 4: Current Density
Ideal characteristics
Series resistanceeffect
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Example 4: Current Density, Cont’d
10 exp
T
VI I
V
V=V2-V1=RID
=>R= V/ID
The ideal diode current is
The non-ideal diode current is:
From the equality of thecurrents we have:
20 exp
T
V RII I
V
2 1 0.170.18
0.67
V VR
I
V1 V2