MSEASUSlides: Muddiest points: Electronic Properties II
-
Upload
mseasuslides -
Category
Education
-
view
442 -
download
0
description
Transcript of MSEASUSlides: Muddiest points: Electronic Properties II
Muddiest Points
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?”
Electronic Properties II: Intrinsic & Extrinsic Semiconductors
Intrinsic Semiconductors
No Dopants
ENER
GY
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
Extrinsic Semiconductors: p-type
p-type Dopants
ENER
GY
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
Extrinsic Semiconductors: n-type
n-type Dopants
ENER
GY
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
Intrinsic - Electron and Hole Migration EN
ERG
Y
- - + +
Si4+
Si4+ Si4+
Extrinsic p-type: Majority Carriers - Holes EN
ERG
Y
Si4+
B3+
*No electric field applied
Extrinsic n-type: Majority Carriers - Electrons EN
ERG
Y
Si4+
P5+
*No electric field applied
Effect of Temperature: Intrinsic
𝛔 = 𝒏𝒊𝒒(𝛍𝒆 + 𝛍𝒉)
𝒏𝒊 ∝ 𝒆−𝑬𝒈
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)
Effect of Temperature: Intrinsic
𝛔 = 𝒏𝒊𝒒(𝛍𝒆 + 𝛍𝒉)
𝒏𝒊 ∝ 𝒆−𝑬𝒈
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)
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
Conductivity Equation
𝛔 = 𝐧𝐪𝛍𝒆 + 𝐩𝐪𝛍𝒉
Intrinsic Semiconductors (n=p=ni)
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))
𝛔 = 𝒏𝒊𝒒(𝛍𝒆 + 𝛍𝒉)
Conductivity Equation: p-type
𝛔 = 𝐧𝐪𝛍𝒆 + 𝐩𝐪𝛍𝒉
Extrinsic Semiconductors: p-type (p>>n)
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))
𝛔 ≈ 𝒑𝒒𝛍𝒉
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 = 𝐧𝐪𝛍𝒆 + 𝐩𝐪𝛍𝒉 𝛔 ≈ 𝒑𝒒𝛍𝒉
𝛍 𝒉= 0.05 (m2/(V-s)) 𝒑= 3.13 x 1021 m-3
𝛔 = (3.13 x 1021 m-3)(1.6x10-19 C)(0.05 m2/(V-s))
𝛔 = 𝟐𝟓. 𝟎𝟒 (Ω-m)-1
Conductivity Equation: n-type
𝛔 = 𝐧𝐪𝛍𝒆 + 𝐩𝐪𝛍𝒉
Extrinsic Semiconductors: n-type (n>>p)
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))
𝛔 ≈ 𝒏𝒒𝛍𝒆
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/(V-s)) and a hole mobility of 0.05 (m2/(V-s)).
𝛔 = 𝐧𝐪𝛍𝒆 + 𝐩𝐪𝛍𝒉 𝛔 ≈ 𝒏𝒒𝛍𝒆
𝛍 𝒆= 0.14 (m2/(V-s)) 𝐧= 3.13 x 1021 m-3
𝛔 = (3.13 x 1021 m-3)(1.6x10-19 C)(0.14 m2/(V-s))
𝛔 = 𝟕𝟎. 𝟏𝟏 (Ω-m)-1
Wrap-Up
• “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?”
Electronic Properties II: Intrinsic & Extrinsic Semiconductors