chapter 1 - week 1
DESCRIPTION
Basic ElectronicTRANSCRIPT
INTRODUCTION TOSEMICONDUCTORS MATERIAL
Chapter 1
Objectives
• Discuss basic structures of atoms
• Discuss properties of insulators, conductors, and
semiconductors
• Discuss covalent bonding
• Describe the conductions in semiconductor
• Discuss N-type and P-type semiconductor
• Discuss the diode
• Discuss the bias of a diode
EKT 102: Basic Electronic Engineering
Lecture’s Content
1.1 Atomic structure
1.2 Semiconductor, conductors and insulators
1.3 Covalent bonding
1.4 Conduction in semiconductors
1.5 N-type and P-type semiconductors
1.6 Diode
1.7 Biasing the diode
1.8 Voltage-current characteristic of a diode
1.9 Diode models
1.10 Testing a diodeEKT 102: Basic Electronic Engineering
1.1 Atomic Structure
ATOM
Basic structure
Atomic number
Electron shells
Valence electron
Ionization
EKT 102: Basic Electronic Engineering
1.1 Atomic Structure (cont.)
The Atom
1. Atom is the smallest particle of an element that retains the characteristics of that element.
2. An atom consists of the protons and neutrons that make up the nucleus (core) at the center and electrons that orbit about the nucleus.
The nucleus carries almost the total mass of the atom.
Figure 1: The Bohr model of an atom
EKT 102: Basic Electronic Engineering
1.1 Atomic Structure (cont.)
Carry negative charge
Carry positive charge
Neutral(carry no charge)
EKT 102: Basic Electronic Engineering
Figure 2:
1.1 Atomic Structure (cont.)
EKT 102: Basic Electronic Engineering
++ +
Proton+ Electron Neutron
NucleusNucleus
Figure 3: Bohr model of hydrogen and helium
(a) Hydrogen (b) Helium
Num. of protons = Num. of electrons Electrically balanced (neutral) atom
1.1 Atomic Structure (cont.)
EKT 102: Basic Electronic Engineering
Figure 4: The periodic table of the elements
1. Element in periodic table are arranged according to atomic number.
2. Atomic number equals number of protons in nucleus which is the same as the number of electron in an electrically balanced atom .
1.1 Atomic Structure (cont.)
EKT 102: Basic Electronic Engineering
Electrons and Shells
1. Electrons near the nucleus have less
energy than those in more distant
orbits.
2. Each distance (orbit) from the
nucleus corresponds to a certain
energy level.
3. In an atom, the orbits are grouped
into energy levels = shells.
4. A given atom has a fixed number of
shells and each shell has a fixed
maximum number of electrons.
Figure 5: Bohr model of the silicon atom
1.1 Atomic Structure (cont.)
EKT 102: Basic Electronic Engineering
Valence shell
+ -- -
-
--
-
-
-
--
--
-
-
-
-
-
-
-
--
--
-
-
-
-
-
29 n
29 p
Shell 1
Shells or orbital paths
Valence electron
Valence Electron1. Valence shell is the outermost
shell in an atom that determines the conductivity of an atom.
2. The electrons in valence shell are called valence electrons.
3. Valence electrons have higher energy and are less tightly bound to the atom.
Figure 6: Bohr model of copper atom (Cu)
Shell 2
Shell 4
Shell 3
1.1 Atomic Structure (cont.)
EKT 102: Basic Electronic Engineering
The Maximum Number of Electrons in Each Shell
1. The maximum number of electrons (Ne) in each shell is calculated using formula below:
where = number of shell.
2. Example for the copper atom (Cu) shell :
22nNe
Atomic number = 29 = 29 electrons
1st shell :
2nd shell :
3rd shell :
4th shell :
2+8+18=28
1.1 Atomic Structure (cont.)
EKT 102: Basic Electronic Engineering
Ionization
1. When atom absorb energy (e.g heat source) the energies of the electron are raised.
2. Valence electron obtain more energy and more loosely bound to the atom compared to the inner electron.
3. If a valence electron acquires sufficient energy – escape from the outer shell and the process of losing valence electron called ionization.
4. The resulting positively charged atom is called a positive ion.
5. The escape electron is called free electron.
6. On the other hand, the atom that has acquired the extra electron is called a negative ion.
7. This can occur in certain atoms when a free electron collides with the atom and is captured (e.g ).
+Nucleus
Figure 6: Ionization of hydrogen atom (H)
-+
Nucleus
1.2 Semiconductors, conductors and insulators
EKT 102: Basic Electronic Engineering
Material
Insulators Semiconductors Conductors
In terms of electrical properties
All materials are made up of atoms that contribute to its ability to conduct electrical current
1.2 Semiconductors, conductors and insulators
EKT 102: Basic Electronic Engineering
1. An atom can be represented by the valence shell and a core.
2. A core consists of all the inner shells and the nucleus.
+6 for nucleus, -2 for the two inner-shell electrons(net charge +4)
Valence shell = -4e
Inner-shell = -2e
Nucleus: 6 protons 6 neutrons
Figure 7: Diagram of a carbon atom
1.2 Semiconductors, conductors and insulators (cont.)
EKT 102: Basic Electronic Engineering
Insulators Material does not conduct electrical current (e.g rubber, plastic, glass). Valence electron are tightly bound to the atom – very few free electron.
Conductors Material that easily conducts electrical current. The best conductors are single-element material (e.g copper, silver, gold, aluminum). Only one valence electron very loosely bound to the atom - free electron.
Semiconductors Material between conductors and insulators in its ability to conduct electric current. In its pure (intrinsic) state is neither a good conductor nor a good insulator. Most common semiconductor - silicon, germanium, and carbon which contains four
valence electrons.
1.2 Semiconductors, conductors and insulators (cont.)
EKT 102: Basic Electronic Engineering
Band gap - the difference between the energy levels of any two orbital shells. Band - another name for an orbital shell (valence shell = valence band). Conduction band – the band outside the valence shell where it has free electrons.
Figure 8: Energy diagram for three types of materials
Band Gap
The amount of energy that a valence electron must have to jump from the valence band to conduction band.
1.2 Semiconductors, conductors and insulators (cont.)
EKT 102: Basic Electronic Engineering
Band Gap (cont.)
Figure 10: Energy band diagram for an unexcited (no external energy) atom in a pure (intrinsic) Si crystal.
Conduction band
Energy
E3 = 0.7eV
E1
E2
E4 = 1.8eVEnergy gap
E = energy level
Valence band
1.2 Semiconductors, conductors and insulators (cont.)
EKT 102: Basic Electronic Engineering
Comparison of a Semiconductor Atom to a Conductor Atom
1. A valence electron in Si atom feels an attractive
force of +4 compared to Cu atom which feels an
attractive force of +1.
2. Force holding valence electrons to the atom in
Si > in Cu.
3. The distance from its nucleus of Cu’s valence
electron (in 4th shell) > Si’s valence electron (in
3rd shell).
4. The valence electron in Cu has more energy than
the valence electron in Si.
5. Easier for valence electrons in Cu to acquire
enough additional energy to escape from their
atoms and become free electrons than in Si.
Figure 11: Bohr diagrams of the silicon and copper atoms.
14 protons – 10 electrons
29 protons – 28 electrons