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BASIC ELECTRONICS
WHAT IS ELECTRONICS?
Electronics is a branch of physics that deals with the emission and effects of electrons in materials.
Or
Is a branch of science dealing with the study and development of circuit involving semi conductors, logic gates and other electrical components like resistors, capacitors and inductors.
Or
This is the branch of physics which deals with the movement of electricity in different materials.
Electronic system or circuit is made up various components connected to each other. They are used to perform a wide variety of tasks. The main uses of electronic circuit are;
1. Conversion and distribution of data.
2. Controlling and processing of data.
Electronic components can be passive or active:
1. PASSIVE COMPONENTS
Consume but do not produce energy. They do not have the ability to produce GAIN that is to increase the power or AMPLIFY the signal. They also do not have directionally, that’s they operate in the same way regardless of the direction of the current flowing through them passive components include power sources (battery or generator), resistor, capacitor and inductors.
2. ACTIVE COMPONENTS
These are those that have direction and or the capacity to produce gain. They include semi conductor devices such as diodes, transistors and integrated circuits.
Additional terms
Voltmeter – is the device that measure potential difference.
Ammeter – is the device which record electric current.
Inductors – These are coils wound out soft iron core used to control alternating current by self induction.
Also used to minimize effect of excessive alternating current in the electric circuit. Usually
inductors are made up by a copper wire.
ENERGY BANDS IN SOLIDS
The energy band in sold is the range of energy possessed by an electron in solid materials (crystals).
This happens when atoms of element combine to form solid materials, they arrange themselves in an orderly manner called crystal. Therefore the energy levels of the electrons of the atoms in a solid are modified and thus each electron in any orbit of an atom can have a number of discrete but closed spaced energy level lying within a certain range.
The energy bands formed when the atom combined to form a solid one of three categories;
- Valence band
- Conduction band
- Forbidden gap
An important parameter in the band theory is the Fermi level, the top of the available electron energy levels at low temperatures. The position of the Fermi level with the relation to the conduction band is a crucial factor in determining electrical properties.
1. VALENCE BAND
This is the range of energy possessed by valence electron. It has the electrons of highest energy. The band may be completely or partially filled with electrons, where the electrons are normally present at the absolute zero temperature.
2. CONDUCTION BAND
This is the range of energies possessed by conduction free electrons. The band may be partially or not filled with electrons.
3. FORBIDDEN ENERGY GAP
This is the energy of separation between conduction band and valence band.
No electrons of solid can stay in this band.
CLASSIFICATION OF SOLIDS WITH ENERGY BANDS
Due to the arrangement of electrons in energy bands leads to the formation of three types of solids in terms of conductivity which are;
- Conductors (metal)
- Semi conductors
- Non – conductors (or insulators)
1. ENERGY BAND IN CONDUCTORS (METAL)
CONDUCTORS
This is the material which can conduct electricity at any temperature.
Or
Conductors are those substances which easily allow the passage of current by means of free electrons through them.
- Absence of forbidden gap.
- Valence band and conduction band overlap one another.
 PROPERTIES OF A CONDUCTOR
- Its electricity conductivity decrease with temperature.
- This is due to some electrons loss amount of energy due to collision.
1. ENERGY BAND IN THE NON – CONDUCTOR (INSULATED)
NON – CONDUCTOR
This is the material which cannot conduct electricity at any temperature.
Or
These are the materials which do not allow the passage of electric current by means of free electrons through them.
- The energy band in non – conductor arranged as follows.
- The valence band is completely filled with electrons.
- The conduction band is empty.
- The forbidden energy gape is large about 15ev. And therefore valence electrons from the valence band can never gain enough energy to overcome the forbidden energy gap.
PROPERTIES OF INSULATOR
- The forbidden gap is higher which makes a given electrons an efficient to jump from valence band to conduction band.
- Presence of higher electrons at in force.
- Cannot conduct electricity.
 ENERGY BAND IN SEMICONDUCTOR
SEMICONDUCTOR
This is a material which behaves as an insulator at OK and conductor at 273K.
Or
This is the material which has the properties lies between that of insulator and conductor.Examples of semiconductors are silicon, germanium, cadmium sulphide and gallium arsenide.
a) At absolute zero temperature (OK)
A semi conductor acts like a non – conductor. The valence band completely filled with electrons, and conduction band is completely empty. Forbidden gap is wide.
b) At room temperature
A semiconductor acts like a conductor:
- The valence band is partially filled.
- Conduction band has few electrons.
- For bidden energy gap is narrow.
PROPERTIES OF SEMICONDUCTOR
- Presence of narrow for bidden gap.
- Its conductivity increases with temperature.
- Presence of partial electrons in the conduction on band.
- They have negative temperature coefficient of resistance.
EFFECTS OF TEMPERATURE IN SOLIDS
- EFFECTS OF TEMPERATURE IN NON CONDUCTOR (INSULATED)
The temperature has no effect on the conductivity property of the insulator since the forbidden energy gap is very large.
2. EFFECTS OF TEMPERATURE IN A CONDUCTOR
The conductivity of the conductor decrease as the temperature increases. Since when the temperature increase, it rises the amplitude of vibration of atoms and more collision with atoms are made by drifting electrons and this slow the free electrons and hence conductivity decrease.
3. EFFECTS OF TEMPERATURE IN SEMI CONDUCTORS
At absolute zero temperature.
At this temperature the valence band is full filled and there is a large energy gap between valence and conduction’s band. There is no valence electron can reach the conduction band to become free electron, thus the material behaves like an insulator.
Above absolute zero temperature, as the temperature rises some valence electrons acquire sufficient energy to enter into the conduction band and this becomes free elections. Thus the conductivity increases as the temperature increases.
TYPES OF SEMICONDUCTORS
There two types of semiconductors:-
a)Â Intrinsic semiconductor
These are pure semiconductors which the charge carrier originates inside the material itself. The conduction of electricity takes place by the promotion of electrons from the valence to the conduction band energy bands in intrinsic semiconductor. The conductivity in this semiconductor is due to increase in temperature and the main charger carrier is electron.
In intrinsic semiconductor, the number of free electrons and the number of holes are exactly equal.
b)Â Extrinsic semiconductors (Impure semi conductor)
This is type of a semiconductor which is conduction are introduced and improved through the doping process. In these types of semiconductor you can modify conduction level by adding small amount of impurity up to a million times.
DOPING
Doping is process of adding impurity atoms to intrinsic crystal to produce an extrinsic semiconductor.
OR
This is the process of adding an impurity is to increase the number of free electrons or holes in the semiconductor. The purpose of adding impurities is to increase the number of free electrons or holes in the semiconductor in order to increase the conductivity of the semiconductor. The impurities are called dopants.
MECHANISM OF DOPING SEMICONDUCTORS
Both silicon and germanium are tetravalent atoms, ie they have for valence electrons (four electrons to the outermost shell of the atom ).
If pentavalent atom (eg. phosphorus) replace a silicon semiconductor, four of the impurity electron play the same role as the four valence electrons of the replaced sililcon atom and become part of the valence band.
The fifth valence electron is easily detected from the pentavalent atom by thermal energy and moves freely in the conduction band. Impurities that denote electrons to the conduction band are called donor impurities.
Free electron
Free electron
Fig 1.0
Effect of adding a donor impurity to a silicon semiconductor.
Doping produces two types of semiconductors which are:-
- n – type semiconductor
- p – type semiconductor
This is the semiconductor which the majority charge carriers are electrons. (Negativity charges)
The n – type semiconductor obtained by adding the pentavalent element to the pure semiconductor (Trivalent element) the addition of pentavalent impurities provides a large number of free electrons in a semi conductor.
The pentavalent impurities are called donors since they provide free electrons to the semiconductors. Suppose a pentavalent element e.g. antimony atom is added to a pure germanium trivalent atom s shown below;
Si – silicon
Sb – Antimony atom
The form valence electrons of Antimony will form bonding with the germanium valence electrons. The fifth valence electron of antimony is not involved in bonding, so remain free to move thus the number of electrons carries increases and hence the conductivity of material increases.
ENERGY BAND OF N – TYPE SEMICONDUCTOR
The additional of donor impurities to an intrinsic semiconductor, creates extra energy level called donor energy level just below the bottom of the conduction band at the forbidden band.
- P – Type of semiconductor
This is a semiconductor which the majority charge carries are positive charges holes. The p – type semiconductor obtained by adding trivalent impurities to the pure semiconductor. The additional of trivalent impurities provides a large number of holes in the semiconductor.
The trivalent impurities are called an acceptor since it receives the electron from the semiconductor. Suppose a trivalent element e.g. indium atom is added to a pure semiconductor of germanium (trivalent) atom as shown below;
 Â
The three valence electron of germanium form complete bonding in the indium the fourth bond is complete being short of one electron. This missing electron is called a hole. Therefore each indium atom added one hole is created. The number of positive charge carrier’s increases and this increases the conductivity of the material. The charge carries of current are positive charge.
ENERGY BAND IN P – TYPE SEMICONDUCTOR
The additional of acceptor impurity to an intrinsic semiconductor creates extra energy level called acceptor energy level just above the top of the valence band
COMPARISON BETWEEN EXTRINSIC AND INTRINSIC SEMICONDUCTOR
          INTRINSIC SEMICONDUCTOR |
            EXTRINSIC SEMICONDUCTOR |
| It is a pure semiconductor. | It is an impure semiconductor. |
| The number of electricity equals to the number of holes. | The number of free electrons not equal to the number of holes. |
| The electric conductivity is low. | The electric conductivity is high. |
| The electric conductivity depend on temperature. | The electric conductivity depend on the temperature and amount of doping. |
| It has no practical use. | Used in electronic device. |
COMPARISON BETWEEN N – TYPE AND p – TYPE SEMICONDUCTOR
|                        N – TYPE |                            P – TYPE |
| Produced by adding pentavalent impurities to a pure semiconductor. | Produced by adding trivalent impurities to a pure semiconductor. |
| The number of free electron exceed the number of holes. | The number of holes exceeds the number of free electrons. |
| The majority charge are negative charges. | The number of holes exceed the number of free electrons. |
| The donor energy level is just below the bottom of the conduction band. | The acceptor energy level is just above the valence band. |
