Name: Semiconductor Devices vs Vacuum Tubes
Uploaded: 2019-07-19
Duration: 5 min 16 s
Description: Learn in a detailed manner about the uses of semiconductor devices such as P-N junction diode, transistor etc. Also, learn the working principle of vacuum tu...

Question

Explain the structure of p-type and n-type semiconductor and draw energy band diagram of it.

Accepted Answer

A n-type semiconductor is created by doping pure silicon crystal lattice with a pentavalent impurity element like $Arsenic (As)$ . In an N-type semiconductor the atom of pentavalent impurity element $Arsenic (As)$ is in between $silicon$ atoms. The Silicon atoms have four electrons in the valence shell. Each of the silicon atom creates a covalent bond with an electron of the prevalent impurity atom

The impurity element electron form covalent bonds with only four silicon atoms. The fifth electron of the impurity atom is not bonded with any semiconductor atom in the crystal lattice. This electron is loosely bonded to its parent impurity atom. Thus, as external voltage or heat is applied this fifth electrons easily breaks its bond with the parent atom and takes part in conduction.This fifth electron majorly contributes to the current in an N-type semiconductor.In the N-type Semiconductor the electrons become the majority carrier.

A p-type semiconductor is created using trivalent impurity like $Gallium$ , having three valence electrons is added to $Germanium$ crystal in a small amount. Each atom of the impurity fits in the $Germanium$ crystal in such a way that its three valence electrons form covalent bonds with the three surrounding $Germanium$ atoms.

In the fourth covalent bonds, only the germanium atom contributes one valence electron, while gallium atom has no valence bonds. Hence, the fourth covalent bond is incomplete, having one electron short. This missing electron is known as a Hole. Thus, each gallium atom provides one hole in the germanium crystal.

As an extremely small amount of Gallium impurity has a large number of atoms, therefore, it provides millions of holes in the semiconductor.

Explain the structure of p-type and n-type semiconductor and draw energy band diagram of it.

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