Semiconductors

Semiconductors are materials that have properties in between that of a normal conductor and that of an insulator.

#1.2 Properties Of A Semiconductor

A semiconductor resistance decreases as its temperature increases, unlike metals whose resistance increases with increase in temperature.
Semiconductors have a crystalline structure of four valence electrons.
Example of common semiconductors are silicon and germanium.

#1.2.2 Electrons And Holes

When a semiconductor is at the lowest possible temperature, in the atom all the the electrons are firmly bounded to the nucleus, there are no free electrons. But when at room temperature thermal energy will be acquired by the electrons, if the thermal energy acquired is stronger than the energy binding the electrons to the nucleus, the electrons breaks free from the bond and becomes a 'free electron' by moving out of its position in the atom leaving a vacany called a hole which is equivalent to a positive charge +e.
An electron in a near by atom will be attracted to fill this hole create.
If this semiconductor is connected to a battery, the holes will move towards its negative terminal and the electrons will move towards the positive terminal.
All pure semiconductors have equal number of holes and electrons.

#1.3 Doping Effect

Doping is the adding of impure materials into pure semiconductors to alter the structure of the semiconductor crystal.
#1.4 n - type Semiconductor
A n - type semiconductor is produced by adding an element such as arsenic or antimony to a germanium semiconductor.
This produces more electrons in the semiconductor making it have negative charge.
#1.5 p - type Semiconductor
A p - type semiconductor is produced by adding an element such as indium or boron to a silicon semiconductor.
This produces more holes in the semiconductor making it have positive charge.

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