Semiconductor: Types, Properties, and Application

Semiconductor

• Semiconductors have 4 electrons in their external orbit. Example:- Si-14, Ge-32.
• Pure semiconductor is called Intrinsic semiconductor. 
• Doped semiconductor is called Extrinsic semiconductor.
• Doping can be done by pentavalent impurity and trivalent impurity.

Types of Semiconductor

According to Type of Impurity, semiconductor are of two types:

1. N-type (formed by doping of pentavalent impurities like bismith, arsenic, antimony and phosphorus).
2. P-type (formed by doping of trivalent impurites like boron, indium, gallium, alluminium).

Properties of Semiconductor

1. Si has Forbidden Energy Gap of 1.12 eV and Ge has forbidden energy gap of 0.72 eV.
2. Semiconductors have negative Temperature Co-efficient of resistance i.e. With increase in temperature their resistance decreases like insulators.

Application of Semiconductor

When one half of any semiconductor substrate is dopped with p-type impurity and other half with n-type of impurity, a junction is formed called P-N Junction. This junction acts as barrier for charge carriers to flow from one side to another side.

1. The process of applying external voltage on both sides of substrate is called Biasing.
2. When positive dc voltage is applied to p-side and negative voltage is applied to n-side, this biasing is called Forward Biasing.
3. When negative dc voltage is applied to p-side and positive voltage to n-side, this type of biasing is called Reverse Biasing.
4. In forward biased, Voltage required to break the barrier is called Knee Voltage which value is 0.72 v for Si and 0.32 v for Ge.
5. In reverse biased, Voltage required to break the barrier is called Reverse Break-down Voltage.
6. P-N junction is called a Diode. Diodes are used for switching, rectification, voltage regulation etc application.
7. Depending upon construction and practical application Types of Diodes are zenor diode, light emitting diode, photo diode, tunnel diode, varactor diode etc.

Reference:

Albert Malvino and David J Bates, “Electronic Principles”, 7th Edition, TATA McGRAW HILL.