I I T M SEMICONDUCTOR Presentation On IITM, E C-2ND YEAR 0915EC081070 PRESENTED BY:- SATYENDRA YADAV IITM, E C-2ND YEAR 0915EC081070

CONTENTS Introduction Types of semiconductor Chemical bond in semiconductor Effect on semiconductor Applications Conclusion

INTRODUCTION A semiconductor is a material that has an electrical conductivity between that conductor and an insulator, that is, generally in the range103 siemens/cm to 10−8 S/cm. Devices made from semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other devices.

Types of semiconductor INTRINSIC An intrinsic semiconductor, also called an undoped semiconductor or i-type semiconductor, is a pure semiconductor without any significant dopant species present. The number of charge carrier is therefore determined by the properties of the material itself instead of the amount of impurities. In intrinsic semiconductors the number of excited electrons and the number of holes are equal: n = p.

Types of semiconductor(cont.) EXTRINSIC An extrinsic semiconductor is a semiconductor that has been doped, that is, into which a doping agent has been introduced, giving it different electrical properties than the intrinsic(pure)semiconductor. The two types of extrinsic semiconductor:- N-type semiconductors:- Extrinsic semiconductors with a larger electron concentration than hole concentration are known as n type semiconductor. P-type semiconductors:- As opposed to n-type semiconductors, p type semiconductor have a larger hole concentration than electron concentration.

Chemical bond in semiconductor Semiconductor like germanium and silicon have crystalline structure. both these material are tetravalent. Each has four valance electrons in outermost shell. These four electrons are known as valance electrons. and these four valance electrons made four covalent bond with other atom of silicon and germanium.

Effect on semiconductor The electrical conductivity of a semiconductor changes appreciably with temperature variations. At very low temperature. the semiconductor crystal behaves as a perfect insulator since the covalent bonds are very strong and no free electron are available. but at room temperature, some of the covalent bonds are broken due to thermal energy supplied to the crystal. due to breaking Of the bonds, some electrons become free. And the resistance of semiconductor decreases with the increase in temperature and vice verse.

Applications Science and industry also rely heavily on semiconductor devices. Research laboratories use these devices in all sorts of electronic instruments to perform tests, measurements, and numerous other experimental tasks. Industrial control systems (such as those used to manufacture automobiles) and automatic telephone exchanges also use semiconductors.

Conclusion Holes contribute to current in valance band (VB) as e-’s are able to create current in conduction band (CB). Hole is not a free particle. It can only exist within the crystal. A hole is simply a vacant electron state. A transition results an equal number of e- in CB and holes in VB. This is an important property of intrinsic, or undoped s/c’s. For extrinsic, or doped, semiconductors this is no longer true.

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