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7/26/2019 ELE232 - Chapter 1- Semiconductor [Compatibility Mode]-4
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ELE 232 ELECTRONICS
Prepared By:
Norsabrina Sihab
Faculty of Electrical Engineering,
Universiti Teknologi MARA
Pulau Pinang
Tel : 04-3823355
Email : [email protected]
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Chapter : SEMICONDUCTOR MATERIAL
Norsabrina Sihab
Faculty of Electrical Engineering,
Universiti Teknologi MARA
Pulau Pinang
Tel : 04-3823355
Email : [email protected]
Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
Learning Outcome
At the end of this chapter, students able to:
Discuss the basic structure of atoms, energy band, covalent
bonds, conduction in semiconductor, free electrons andholes as carrier.
Describe intrinsic, doping and extrinsic semiconductor
Describe the properties of n-type and p-type semiconductors
3Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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Introduction
Electronics devices are complex component which mostly used inelectronics systems:
Communication (TV, radio)
Digital system (PC, calculator) Industrial system (robotic, process control)
Medical system (x-ray, ECG)
Instrumentation (oscilloscope)
Since 1940s, electronics system constructed using solid-statecomponents.
Solid state components are made from semiconductor elements,neither conductor nor insulator, has useful characteristics as an
amplifier or rectifier.
7/26/2019 ELE232 - Chapter 1- Semiconductor [Compatibility Mode]-4
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7/26/2019 ELE232 - Chapter 1- Semiconductor [Compatibility Mode]-4
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Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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Conductor, Semiconductor & Insulator
Figure 1.3 - Energy diagrams for the three types of materials(insulator, semiconductor, and conductor)
Energy gap > The difference in energy between the valence bandand the conduction band. This is the amount of energy required for avalence electrons to jump from valence band to conduction band.
Once at conduction band, electrons is free to move throughout thematerial and is not tied to any given atom. For example, it absorb anamount of energy 1.8eV-0.7eV=1.1eV (for Si material).*1eV=1.6X10-9J.
Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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Current in Semiconductors
Energy Level -> Electrons orbit the nucleus of an atom at certaindistance from the nucleus. Electrons near the nucleus have less
energy. Each distance from nucleus corresponds to a certainenergy level.
Conduction band
e-
(valence e-)
e- (free electron)
Figure 1.5 Energy Level
Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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Current in Semiconductors
Free Electrons > When an electron acquires enough energy (fromheat energy), it can leave the valence band and become a free electronwhich its exist in conduction band.
Conduction band > Band outside valence band which level ofenergy of an electron is high enough and capable of being influence byan external force.
Figure 1.6 Creation of EHPs
Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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Current in Semiconductors
Covalent Bond -> Is a method by which atoms complete theirvalence shells by sharing valence e- with other atoms. It strongbonding between atoms. Eg. Si atom has 4 valence e- and it create
8 shared valence e-
of each atom. When Si atoms combined bycovalent bonding it form a solid material.
Figure 1.7 - Covalent bonding of the silicon atom.
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Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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Current in Semiconductors
Conduction Versus Temperature > At room temperature pure Sihas no free e-. Semiconductor has no free electrons when no
voltage applied. As temperature increase, electrons will absorbenough energy to break their covalent bonds and number of freeelectrons will increase. As temperature decrease, less thermalenergy to release the e- from their covalence band and number ofelectrons will decrease. Conductivity of semiconductor temperature. When circuit is warm up, current will increase.
Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
N-type & P-type Semiconductor
Intrinsic Semiconductor > Semiconductor which has a very lowlevel of impurities. Intrinsic Si & Ge poor conductor (relatively
large energy gap)Extrinsic Semiconductor > Semiconductor that has been subjectedto a doping process. Not longer as pure/intrinsic material.
Doping - Is a process of adding impurities atoms to the intrinsic Sior Ge to improve the conductivity of a semiconductor.
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Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
N-type & P-type Semiconductor
Two types of impurities:
1. Trivalent > To increase the number of holes in intrinsicsemiconductor. It has 3 valence electrons. Known as acceptor
(accept electrons). Eg. Aluminum (Al), Gallium (Ga), Boron(B), Indium (In). Trivalent doped with Si/Ge is called a p-typesemiconductor.
2. Pentavalent > To increase the number of conduction bandelectrons in intrinsic semiconductor. It has 5 valenceelectrons. Known as donor (donate electrons). Eg.Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi).Pentavalent doped with Si/Ge is called a n-type
semiconductor.
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Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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N-type & P-type Semiconductor
Two types of extrinsic semiconductor (material that are subjectedto doping process):
1. n-type > negative charge of electrons. Created by adding
impurity element with 5 valence electrons into pure Si or Ge.Electrons are majority carriers. Holes created by EHP areminority carrier.
2. p-type > positive charge of hole. Holes are majority carrier.Electrons are minority carrier.
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Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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N-type & P-type Semiconductor
Pentavalent impurity atom in a silicon crystalstructure. An antimony (Sb) impurity atom isshown in the center. The extra electron from theSb atom becomes a free electron.
Trivalent impurity atom in a siliconcrystal structure. A boron (B) impurityatom is shown in the center.
Figure 1.10 Trivalent and pentavalent impurities
Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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N-type & P-type Semiconductor
Figure 1.11 N-type semiconductor
Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
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N-type & P-type Semiconductor
Figure 1.12 P-type semiconductor
Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
p-n Junction
P-N junction > formed by p-type region jointed with n-typeregion.
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Figure 1.13 - The basic diode structure at the instant of junction formationshowing only the majority and minority carriers.
C S C S
7/26/2019 ELE232 - Chapter 1- Semiconductor [Compatibility Mode]-4
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Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
Exercise
29Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
Exercise
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Chapter 1 Semiconductor Material
Updated Nov 2013LE232 Electronics 1Norsabrina Sihab
Exercise
1. Define the following terms:
a) Free electron
b) Intrinsic material
c) Ionization
2. Define covalent bonding and sketch a diagram showing thecovalent bonding of the silicon atom.
3. Explain the concepts of electron hole pair (EHP) and Lifetime ofEHP.
4. Draw the energy diagrams of conductor, semiconductor andinsulator.
5. Describe the difference between n-type and p-typesemiconductor materials.
6. Describe the differences between majority and minoritycarriers.
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