INSULATORS
Insulators are such materials in which the conduction cannot take place, due to the large forbidden gap.
Examples: Wood, Rubber.
The following are the characteristics of Insulators:
· The Forbidden energy gap is very large.
· Valance band electrons are bound tightly to atoms.
· The value of forbidden energy gap for an insulator will be of 10eV.
· For some insulators, as the temperature increases, they might show some conduction.
· The resistivity of an insulator will be in the order of 107 ohm-meter.
SEMICONDUCTORS
Semiconductors are such materials in which the forbidden energy gap is small and the conduction takes place if some external energy is applied.
Examples: Silicon, Germanium.
The following are the characteristics of Semiconductors.
· The Forbidden energy gap is very small.
· The forbidden gap for Ge is 0.7eV whereas for Si is 1.1eV.
· A Semiconductor actually is neither an insulator, nor a good conductor.
· As the temperature increases, the conductivity of a semiconductor increases.
· The conductivity of a semiconductor will be in the order of 102 mho-meter.
CONDUCTORS
Conductors are such materials in which the forbidden energy gap disappears as the valence band and conduction band become very close that they overlap.
Examples: Copper, Aluminum..
The following are the characteristics of Conductors.
· There exists no forbidden gap in a conductor.
· The valance band and the conduction band gets overlapped.
· The free electrons available for conduction are plenty.
· A slight increase in voltage, increases the conduction.
· There is no concept of hole formation, as a continuous flow of electrons contribute the current.
Band-Gaps in Conductors, Semiconductors & Insulators
There is a necessity to discuss a few important terms here before we move on:
CURRENT
It is simply the flow of electrons. A continuous flow of electrons or charged particles, can be termed as Current. It is indicated by I or i. It is measured in Amperes. This can be alternating current AC or direct current DC.
VOLTAGE
It is the potential difference. When there occurs a difference in potentialities, between two points, there is said to be a voltage difference, measured between those two points. It is indicated by V. It is measured in Volts.
RESISTANCE
It is the property of opposing the flow of electrons. The possession of this property can be termed as resistivity. This will be discussed later in detail.
With the terms discussed above, we have a standard law, which is very crucial for the behavior of all the electronic components, called as Ohm’s Law.
This states the relation between current and voltage in an ideal conductor.
According to Ohm’s law, the potential difference across an ideal conductor is proportional to the current through it.
V α I
An ideal conductor has no resistance. But in practice, every conductor has some resistance in it. As the resistance increases, the potential drop also increases and hence the voltage increases.
Hence the voltage is directly proportional to the resistance it offers.
V α R
V=IR
But the current is inversely proportional to the resistance.
V α I α 1/R
I=V/R
Hence, in practice, an Ohm’s law can be stated as −
According to Ohm’s law, the current flowing through a conductor is proportional to the potential difference across it, and is inversely proportional to the resistance it offers.
This law is helpful in determining the values of unknown parameters among the three which help to analyze a circuit.
A semiconductor is a substance whose resistivity lies between the conductors and insulators. The property of resistivity is not the only one that decides a material as a semiconductor, but it has few properties as follows.
· Semiconductors have the resistivity which is less than insulators and more than conductors.
· Semiconductors have negative temperature co-efficient. The resistance in semiconductors, increases with the decrease in temperature and vice versa.
· The Conducting properties of a Semiconductor changes, when a suitable metallic impurity is added to it, which is a very important property.
Semiconductor devices are extensively used in the field of electronics. The transistor has replaced the bulky vacuum tubes, from which the size and cost of the devices got decreased and this revolution has kept on increasing its pace leading to the new inventions like integrated electronic.
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