1. INTRODUCTION TO SEMICONDUCTORS MATERIAL Chapter 1

2. 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

3. 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 diode EKT 102: Basic Electronic Engineering

4. 1.1 Atomic Structure ATOM Basic structure Atomic number Electron shells Valence electron Ionization EKT 102: Basic Electronic Engineering

5. 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

6. 1.1 Atomic Structure (cont.) Carry negative charge Carry positive charge Neutral (carry no charge) EKT 102: Basic Electronic Engineering Figure 2:

7. 1.1 Atomic Structure (cont.) EKT 102: Basic Electronic Engineering + + + Proton + Electron Neutron Nucleus Figure 3: Bohr model of hydrogen and helium (a) Hydrogen (b) Helium Num. of protons = Num. of electrons Electrically balanced (neutral) atom

8. 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.

9. 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

10. 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 Electron 1.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) 10 Shell 2 Shell 4 Shell 3

11. 1.1 Atomic Structure (cont.) EKT 102: Basic Electronic Engineering

12. 1.1 Atomic Structure (cont.) EKT 102: Basic Electronic Engineering + Nucleus Figure 6: Ionization of hydrogen atom (H) - + Nucleus

13. 1.2 Semiconductors, conductors and insulators EKT 102: Basic Electronic Engineering Material InsulatorsSemiconductorsConductors In terms of electrical properties All materials are made up of atoms that contribute to its ability to conduct electrical current

14. 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

15. 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.

16. 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.

17. 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 E 3 = 0.7eV E1E1 E2E2 E 4 = 1.8eV Energy gap E = energy level Valence band

18. 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 4 th shell) > Si’s valence electron (in 3 rd 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