This slide set was used to create the MaterialsConcepts YouTube Video "Muddiest points: Electronic Properties II". Here is the link to that video: https://www.youtube.com/watch?v=-MC_YX7ruhs To study the vocab used in this video, visit this site: http://quizlet.com/24383455/72-electronic-properties-ii-intrinsic-extrinsic-semiconductors-flash-cards/ This work was supported by NSF Grants #0836041 and #1226325

1. Muddiest Points
Electronic Properties II:
Intrinsic & Extrinsic Semiconductors
Muddiest Points:
• “What are the differences between intrinsic and
extrinsic semiconductors?”
• “What are the differences between n type and p type
extrinsic semiconductors?”
• “How does temperature affect each type of
semiconductor?”
• “What are the differences in the conductivity equation
for intrinsic and extrinsic semiconductors?”
• “What is the relation of electron and electron-hole
mobility to conductivity?”

2. Intrinsic Semiconductors
ENERGY
No Dopants
 Less than 1021/m3 impurity
atoms (10-6 wt% impurities)
 electron-hole pairs (n=p=ni)
 Conductivity increases with
an increase in temperature
(creates more e-h pairs)
 Energy Gap (Eg) is constant
and between 0.1eV-2eV
 Group IV elemental
semiconductors
 Group III + Group V are
compound semiconductors

3. Extrinsic Semiconductors: p-type
ENERGY
p-type Dopants
 Impurity atoms have one less
valence electron than the host
 Majority Charge Carriers:
electron holes (p>>n)
 Minority Charge Carriers:
electrons (n<<p)
 Acceptor States (contribute
electron holes)
 Saturation = all acceptor states
filled
 Example: Boron (B3+), Group III,
impurity atoms within a Silicon
host (Si4+), Group IV

4. Extrinsic Semiconductors: n-type
ENERGY
n-type Dopants
 Impurity atoms have one more
valence electron than the host
 Majority Charge Carriers:
electrons (n>>p)
 Minority Charge Carriers:
electron holes (p<<n)
 Donor States (contribute
electrons)
 Exhaustion = every donated
electron in Cond. Band
 Example: Phosphorus (P5+),
Group V, impurity atoms within
a Silicon host (Si4+), Group IV

5. Intrinsic - Electron and Hole Migration
ENERGY
Si4+
Si4+
-
Si4+
+-
+

6. Extrinsic p-type: Majority Carriers - Holes
ENERGY
Si4+
B3+
*No electric field applied

7. Extrinsic n-type: Majority Carriers - Electrons
ENERGY
Si4+
P5+
*No electric field applied

8. Effect of Temperature: Intrinsic
𝛔 = 𝒏 𝒊 𝒒(𝛍 𝒆 + 𝛍 𝒉 )
𝒏𝒊 ∝
𝑬𝒈
−
𝒆 𝟐𝒌𝑻
ni = intrinsic carrier density
(# of carriers/m3)
Eg = energy gap (eV)
k = Boltzmann Constant
(8.6173 x 10-16 eV-K-1)
T = Temperature (K)

9. Effect of Temperature: Intrinsic
𝛔 = 𝒏 𝒊 𝒒(𝛍 𝒆 + 𝛍 𝒉 )
𝒏𝒊 ∝
𝑬𝒈
−
𝒆 𝟐𝒌𝑻
ni = intrinsic carrier density
(# of carriers/m3)
Eg = energy gap (eV)
k = Boltzmann Constant
(8.6173 x 10-16 eV-K-1)
T = Temperature (K)

10. Effect of Temperature: Extrinsic
 Freeze-out region: not
enough thermal energy for
dopant activation
 Extrinsic region: limited
temperature effect on
extrinsic conductivity
 Intrinsic region: an
increase in temperature,
increases thermal energy
creating a large number of
electron-hole pairs

11. Conductivity Equation
Intrinsic Semiconductors (n=p=ni)
𝛔 = 𝐧𝐪𝛍 𝒆 + 𝐩𝐪𝛍 𝒉
𝛔 = 𝒏 𝒊 𝒒(𝛍 𝒆 + 𝛍 𝒉 )
σ = conductivity
(ohm-m)-1
ni = intrinsic carrier density
(# of carriers/m3)
q = electric charge
1.6x10-19 (C)
μe = electron mobility
(m2/(V-s))
μh = electron hole mobility
(m2/(V-s))

12. Conductivity Equation: p-type
Extrinsic Semiconductors: p-type (p>>n)
𝛔 = 𝐧𝐪𝛍 𝒆 + 𝐩𝐪𝛍 𝒉
𝛔 ≈ 𝒑𝒒𝛍 𝒉
σ = conductivity
(ohm-m)-1
p = positive carrier density
(# of carriers/m3)
q = electric charge
1.6x10-19 (C)
μh = electron hole mobility
(m2/(V-s))

13. Example 1: p-type Conductivity
What is the conductivity of silicon containing
3.13 x 1021 boron dopant atoms per m3? Silicon
has an electron mobility of 0.14 (m2/(V-s)) and
a hole mobility of 0.05 (m2/(V-s)).
𝛔 = 𝐧𝐪𝛍 𝒆 + 𝐩𝐪𝛍 𝒉
𝛍 𝒉 = 0.05 (m2/(V-s))
𝛔 = (3.13 x 1021
𝛔 ≈ 𝒑𝒒𝛍 𝒉
𝒑= 3.13 x 1021 m-3
m-3)(1.6x10-19 C)(0.05 m2/(V-s))
𝛔 = 𝟐𝟓. 𝟎𝟒 (Ω-m)-1

14. Conductivity Equation: n-type
Extrinsic Semiconductors: n-type (n>>p)
𝛔 = 𝐧𝐪𝛍 𝒆 + 𝐩𝐪𝛍 𝒉
𝛔 ≈ 𝒏𝒒𝛍 𝒆
σ = conductivity
(ohm-m)-1
n = negative carrier density
(# of carriers/m3)
q = electric charge
1.6x10-19 (C)
μe = electron mobility
(m2/(V-s))

15. Example 2: n-type Conductivity
What is the conductivity of silicon containing
3.13 x 1021 phosphorus dopant atoms per m3?
Silicon has an electron mobility of 0.14 (m2/(Vs)) and a hole mobility of 0.05 (m2/(V-s)).
𝛔 = 𝐧𝐪𝛍 𝒆 + 𝐩𝐪𝛍 𝒉
𝛍 𝒆 = 0.14 (m2/(V-s))
𝛔 = (3.13 x 1021
𝛔 ≈ 𝒏𝒒𝛍 𝒆
𝐧= 3.13 x 1021 m-3
m-3)(1.6x10-19 C)(0.14 m2/(V-s))
𝛔 = 𝟕𝟎. 𝟏𝟏 (Ω-m)-1

16. Wrap-Up
Electronic Properties II:
Intrinsic & Extrinsic Semiconductors
• “What are the differences between intrinsic and
extrinsic semiconductors?”
• “What are the differences between n type and p
type extrinsic semiconductors?”
• “How does temperature affect each type of
semiconductor?”
• “What are the differences in the conductivity
equation for intrinsic and extrinsic
semiconductors?”
• “What is the relation of electron and electronhole mobility to conductivity?”