INTRODUCTION


Introduction

There are two types of semiconductor components in electronic and electrical circuits. They are active and passive components. Diodes are the foremost active components and resistors are the foremost passive components in electronic design circuits. Diodes are essentially unidirectional devices having exponential relationship for the current-voltage characteristics are made from semiconductor materials.



DETAILS



The three necessary materials that are utilized in electronics are insulators, semiconductors and conductors. These materials are classified in terms of electrical phenomenon

. Electrical resistivity conjointly known as electrical resistance is a measure of how efficiently a material refuses the electrical current to flow through it. The quality unit of the electrical resistivity is the ohm meter [Ω m]. A material with low electrical resistivity indicates the effective movement of electrical charge throughout the semiconductor. Semiconductors are the materials whose resistivity values are in between insulators and conductors. These materials are neither smart insulators nor smart conductors. They have only a few free electrons because their atoms are tightly bonded in an exceedingly crystalline form are referred to as a “crystal lattice”. Samples of semiconductors are silicon and germanium. Semiconductors have high importance in the manufacture of electronic circuits and integrated devices.

The conductivity of semiconductors can be altered easily by varying the temperature and concentration of doping in the fabrication process. The capability to conduct electricity in semiconductor materials is considerably increased by a adding definite quantity of impurities to the crystalline lattice producing additional free electrons than holes. The properties of semiconductor materials change considerably by adding small amounts of impurities to it. The process of shifting the balance between electrons and holes by incorporating impurity atoms in the silicon crystal lattice is called as doping.

These impurity atoms are known as dopants. Based on the type of doping material incorporated, semiconductor crystals are classified into two types particularly n-type semiconductors and p-type semiconductors. Group –V elements such as phosphorus, antimony and arsenic are usually classified as N-type impurities. These elements have five valence electrons. When N-type impurities are doped into silicon crystal, four of the five valence electrons form four strong covalent bonds with adjacent crystal atoms leaving one free electron. Likewise, every N-type impurity atom produces a free electron in the conduction band which will drift to conduct electric current if a potential is applied to the material. N-type semiconductors can also be referred as Donors. Group–III elements such as boron, aluminium, gallium and indium are usually classified as P-type impurities. These elements have three valence electrons.

When P-type impurities are doped into silicon crystal, all the three valence electrons form three strong covalent bonds with adjacent crystal atoms. There is a deficit of electrons to form the fourth covalent bond and this deficiency is termed as holes. Likewise, every P-type impurity atom produces a hole in the valence band which will drift to conduct electric current if a potential is applied to the material. P-type semiconductors can also be referred as Acceptors.





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