10-12-2012, 03:06 PM
A Presentation on SEMICONDUCTOR
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INTRODUCTION
A semiconductor has electrical conductivity intermediate to that of a conductor and an insulator. Semiconductors differ from metals in their characteristic property of decreasing electrical resistivity with increasing temperature. They typically have narrow bandgaps of < 2 eV
Semiconductors are generally covalently bonded substances.
EXAMPLE OF SEMICONDUCTOR
Certain pure elements found in Group IV of the periodic table are semiconductors. The most commercially important of these elements are silicon and germanium.
Modern synthetic semiconductors include compounds such as GaAs, GaP, InSb, InAs and InP. These have a range of different band gaps.
BAND THEORY
A useful way to visualize the difference between conductors, insulators and semiconductors is to plot the available energies for electrons in the materials. Instead of having discrete energies as in the case of free atoms, the available energy states form bands. Crucial to the conduction process is whether or not there are electrons in the conduction band. In insulators the electrons in the valence band are separated by a large gap from the conduction band, in conductors like metals the valence band overlaps the conduction band, and in semiconductors there is a small enough gap between the valence and conduction bands that thermal or other excitations can bridge the gap.
Semiconductor energy band
For intrinsic semiconductors like silicon and germanium, the Fermi level is essentially halfway between the valence and conduction bands. Although no conduction occurs at 0 K, at higher temperatures a finite number of electrons can reach the conduction band and provide some current. In doped semiconductors, extra energy levels are added.
The increase in conductivity with temperature can be modeled in terms of the Fermi function, which allows one to calculate the population of the conduction band.
Carrier concentration
The concentration of dopant introduced to an intrinsic semiconductor determines its concentration and indirectly affects many of its electrical properties. The most important factor that doping directly affects is the material's carrier concentration. In an intrinsic semiconductor under thermal equilibrium, the concentration of electrons and holes is equivalent.
APPLICATIONS
Semiconductors are of enormous technological importance because of their special properties, which can be modified by doping. Some applications include:
Thermistors
The resistivity of semiconductors varies with temperature. This enables semiconductors to be used as thermometers. Through doping the appropriate sensitivity in the required ranges can be obtained.
POWER SEMICONDUCTOR
There is a form of semi conductor devices which is known as the power semiconductor consisting of devices which have integrated circuits. The applications of these kinds of semiconductor devices take place in those applications which requires very high current or voltage requirements. The semiconductors devices application which involves combination of power semiconductor technology and Integrated Technology (IC) are called as smart power devices. The main use of such devices is in the field of space research.
IR Sensors/Optoelectronic devices
Optoelectronic devices are capable of sensing or responding to light of various wavelengths. This is due to the phenomenon of photo-conductivity whereby a semiconductor can greatly increase its electrical conductivity if the radiation has sufficient energy to promote electrons across the band gap. Many different semiconductors are available with different band gaps to suit particular applications.
MISCILANEOUS USE
semiconductor devices in making high speed computer chips, calculators, telephones and other variety of things like medical equipments and robotics. The research is still going on to find out new avenues and areas where the applications of semiconductor devices can help to gain better results in terms of performance and other parameters.
[attachment=43249]
INTRODUCTION
A semiconductor has electrical conductivity intermediate to that of a conductor and an insulator. Semiconductors differ from metals in their characteristic property of decreasing electrical resistivity with increasing temperature. They typically have narrow bandgaps of < 2 eV
Semiconductors are generally covalently bonded substances.
EXAMPLE OF SEMICONDUCTOR
Certain pure elements found in Group IV of the periodic table are semiconductors. The most commercially important of these elements are silicon and germanium.
Modern synthetic semiconductors include compounds such as GaAs, GaP, InSb, InAs and InP. These have a range of different band gaps.
BAND THEORY
A useful way to visualize the difference between conductors, insulators and semiconductors is to plot the available energies for electrons in the materials. Instead of having discrete energies as in the case of free atoms, the available energy states form bands. Crucial to the conduction process is whether or not there are electrons in the conduction band. In insulators the electrons in the valence band are separated by a large gap from the conduction band, in conductors like metals the valence band overlaps the conduction band, and in semiconductors there is a small enough gap between the valence and conduction bands that thermal or other excitations can bridge the gap.
Semiconductor energy band
For intrinsic semiconductors like silicon and germanium, the Fermi level is essentially halfway between the valence and conduction bands. Although no conduction occurs at 0 K, at higher temperatures a finite number of electrons can reach the conduction band and provide some current. In doped semiconductors, extra energy levels are added.
The increase in conductivity with temperature can be modeled in terms of the Fermi function, which allows one to calculate the population of the conduction band.
Carrier concentration
The concentration of dopant introduced to an intrinsic semiconductor determines its concentration and indirectly affects many of its electrical properties. The most important factor that doping directly affects is the material's carrier concentration. In an intrinsic semiconductor under thermal equilibrium, the concentration of electrons and holes is equivalent.
APPLICATIONS
Semiconductors are of enormous technological importance because of their special properties, which can be modified by doping. Some applications include:
Thermistors
The resistivity of semiconductors varies with temperature. This enables semiconductors to be used as thermometers. Through doping the appropriate sensitivity in the required ranges can be obtained.
POWER SEMICONDUCTOR
There is a form of semi conductor devices which is known as the power semiconductor consisting of devices which have integrated circuits. The applications of these kinds of semiconductor devices take place in those applications which requires very high current or voltage requirements. The semiconductors devices application which involves combination of power semiconductor technology and Integrated Technology (IC) are called as smart power devices. The main use of such devices is in the field of space research.
IR Sensors/Optoelectronic devices
Optoelectronic devices are capable of sensing or responding to light of various wavelengths. This is due to the phenomenon of photo-conductivity whereby a semiconductor can greatly increase its electrical conductivity if the radiation has sufficient energy to promote electrons across the band gap. Many different semiconductors are available with different band gaps to suit particular applications.
MISCILANEOUS USE
semiconductor devices in making high speed computer chips, calculators, telephones and other variety of things like medical equipments and robotics. The research is still going on to find out new avenues and areas where the applications of semiconductor devices can help to gain better results in terms of performance and other parameters.