Extrinsic Semiconductor

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EXTRINSIC SEMICONDUCTOR

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An extrinsic semiconductor is a semiconductor doped by a specific impurity which is able to deeply modify its electrical properties, making it suitable for electronics applications (diodes, transistors, etc.) 

 

The goal of these impurities is to change the electrical properties of the material, specifically (increasing) its conductivity.

Semiconductor doping is the process that changes an intrinsic semiconductor to an extrinsic semiconductor. During doping, impurity atoms are introduced to an intrinsic semiconductor. Impurity atoms are atoms of a different element than the atoms of the intrinsic semiconductor. Impurity atoms act as either donors or acceptors to the intrinsic semiconductor, changing the electron and hole concentrations of the semiconductor. Impurity atoms are classified as donor or acceptor atoms based on the effect they have on the intrinsic semiconductor.

 

Semiconductors and dopant atoms are defined by the column of the periodic table in which they fall. The column definition of the semiconductor determines how many valence electrons its atoms have and whether dopant atoms act as the semiconductor’s donors or acceptors.

Group 4 semiconductor use group 5 atoms as donors and group 3 atoms as acceptors.

 

Group 3-5 semiconductor (compound semiconductor) use group 6 atoms as donors and group 2 atoms as acceptors. Group 3-5 semiconductors can also use group 4 atoms as either donors or acceptors .

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Extrinsic semiconductor are two types p- type semiconductor and n- type semiconductor that  based on doped impurity ( trivalent or pentavalent )

 

p- TYPE SEMICONDUCTOR

In lattice of intrinsic semiconductor Si all four valence electron make covalent bond by sharing  electron with neighboring atoms as shown in figure

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A p-type semiconductor is made by doping of trivalent impurity, these trivalent impurity is called acceptor

If one of the atoms in the intrinsic semiconductor of Si lattice is replaced by an element with three valence electrons (acceptor) such as a Group 3 element like Boron (B) or Gallium (Ga), This impurity will only be able to contribute three valence electrons to the four neighboring atoms of Si in the lattice, therefore one “leaving electron space” is created, this space is called hole .Since holes will “accept” free electrons so Group 3 impurity is also called an acceptor, so an intrinsic semiconductor Si  that has been doped with an acceptor is called a p-type semiconductor

A p-type semiconductor lattice shown below

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In p-type semiconductors, holes are the majority carriers and electrons are the minority carriers.(p>n)

n- TYPE SEMICONDUCTOR

In lattice of intrinsic semiconductor Si all four valence electron make covalent bond by sharing  electron with neighboring atoms as shown in figure

ice screenshot 20160408 033912

 

 

An n-type semiconductor is made by doping of pentavalent impurity in intrinsic semiconductor, these pentavalent impurity is called donor

 

If one of the atoms in the intrinsic semiconductor of Si lattice is replaced by an element with five valence electrons (donor)  such as the Group 5 atoms arsenic (As) or phosphorus (P). In this case, the impurity adds five valence electrons to the four neighboring atoms of Si in the lattice, where it can only hold four. This means that there is now one excess electron in the lattice because it donates an electron,a Group 5 impurity is called a donor

A n-type semiconductor lattice shown below

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In n-type semiconductors, electron are the majority carriers and hole are the minority carriers.(n>p)

Note that the material either p-type or n-type remains electrically neutral.

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