Extrinsic Semiconductor: An extrinsic semiconductor is a semiconductor material that has impurities intentionally added to it. This process is called doping and is used to alter the electrical and optical properties of the material. The impurities added to the semiconductor can be of two types: p-type (positive) and n-type (negative).

In a p-type extrinsic semiconductor, impurity atoms are added that have one less valence electron than the semiconductor atoms. These impurities create holes in the valence band, which can accept electrons from neighboring atoms. The resulting semiconductor material has a higher concentration of holes in the valence band than free electrons in the conduction band. The electrical conductivity of p-type extrinsic semiconductors is primarily due to the movement of holes.

In an n-type extrinsic semiconductor, impurity atoms are added that have one more valence electron than the semiconductor atoms. These impurities create extra electrons in the conduction band, which are free to move and conduct electricity. The resulting semiconductor material has a higher concentration of free electrons in the conduction band than holes in the valence band. The electrical conductivity of n-type extrinsic semiconductors is primarily due to the movement of free electrons.

The doping process changes the band structure of the semiconductor and reduces its bandgap. This makes it easier to excite electrons and create free carriers in the material, leading to an increase in the electrical conductivity. Extrinsic semiconductors also have other interesting properties, such as the ability to create a pn junction when a p-type and an n-type material are placed in contact. The pn junction has unique electronic properties that make it useful in a wide range of electronic devices, including diodes, transistors, and solar cells.

Properties of Extrinsic Semiconductor

Extrinsic semiconductors have several important properties that differ from intrinsic semiconductors due to the intentional addition of impurities. Some of these properties are:

• Electrical conductivity: Extrinsic semiconductors have a higher electrical conductivity than intrinsic semiconductors due to the intentional addition of impurities. The type and concentration of impurities determine the electrical properties of the material.
• Dopant concentration: The concentration of impurities in extrinsic semiconductors is typically much higher than the concentration of thermally generated carriers in intrinsic semiconductors.
• Carrier concentration: The type and concentration of impurities determine the carrier concentration in extrinsic semiconductors. In a p-type material, the concentration of holes is higher than the concentration of free electrons, while in an n-type material, the concentration of free electrons is higher than the concentration of holes.
• Minority carrier lifetime: The addition of impurities to the semiconductor material can reduce the minority carrier lifetime compared to intrinsic semiconductors. This is because the impurities create recombination centers where minority carriers can recombine, leading to a decrease in their lifetime.
• Temperature dependence: The electrical conductivity of extrinsic semiconductors increases with temperature due to increased thermal excitation of free carriers. However, as the temperature increases, the lifetime of the minority carriers decreases due to increased recombination.
• Optical properties: Extrinsic semiconductors have interesting optical properties that depend on the type and concentration of impurities. They can absorb light of certain wavelengths, which can excite electrons and create free carriers in the material.
• PN junction formation: Extrinsic semiconductors can be used to create p-n junctions, which have unique electronic properties that are useful in electronic devices such as diodes, solar cells, and transistors.

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By Team Learning Mantras