ELECTRICAL PROPERTIES OF SEMICONDUCTORS
It is a known fact that electrons revolve round the nucleus in definite circular orbits under the influence of short range attractive forces called nuclear forces. If the potentiality of electron is strong enough to overcome this force of attraction we can designate them as conductors, on the other hand if the energy of electron is least to overcome the nuclear short range forces such materials are called as insulators or in simple words we can say that materials which reveal intermediate behaviour in between conductors and insulators are termed as semiconductors. At Ok semiconductors behave themselves as insulators, because it is general pedagogy that all electrons at Ok will be localised in the valence band. As a result of this electrons cannot jump from conduction band Electrons Energy Valence">valence band to conduction band because they are tightly bounded themselves, even after the application of higher temperatures only few electrons will try to jump to conduction band. So on the whole some of the insulators at OK will behave as a conductor at room temperature.
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The band formed by valence electrons is valence band it is always fulfilled but can never be empty, on the other hand band formed by conduction electrons will serve as conduction band. For an electron to behave as an conductor there should be an unfilled electron in its configuration, the conduction band may be partially filled or empty. Since energy band is nothing but the packet of energy levels, they may be degenerative or non degenerative energy levels depending on the nature of atom. If the atom is in isolated form the energy levels are non degenerative and degenerative in the sense if it is unisolated form. The gap between conduction band and valence band is called forbidden band where the electron cannot stay less than a nanosecond of time. The phenomenon of semiconductors can be best understood with the help of quantam mechanics which specifies the motion of microscopic particles electrons by assuming that the electron has got particle nature and wave nature as proposed by debroglie.
The Term Paper on Conduction Band Electrons Energy Valence
... energy bands. How big is the gap between the valence and conduction bands? How can electrons gain enough energy to move between valence and conduction bands? In a semiconductor the valence band ... is not a spontaneous process: the excited electron is forced into jumping back to the valence band and emitting a photon. What does it ...
Semiconductor is nothing but a crystal where constituent particles like atoms or molecules are arrayed in regular and repeated pattern. Semiconductors are associated with a property called negative temperature coefficient of resistivity, it means resistance of material decreases with the increase of temperature. Whereas conductors will have positive temperature coefficient of resistivity where current increases linearly with voltage, that is the reason why conductors obey ohm’s law in their behaviour. Hence conductors are called as ohmic conductors. Conductors show linear relation between voltage and current. Not all the materials are semiconductors because for example if we take nichrome as an instance, its resistivity lies nearer to semiconductor even then it cannot be deemed as a semiconductor. The table here provides the list of semiconducting materials and their resistivity values.
Semiconductors depending on their conducting properties can be classified into 2 types
1. Intrinsic semiconductors
2. Extrinsic semiconductors
INTRINSIC SEMICONDUCTORS:-
Basically charge carriers present in semiconductors are electrons and holes, electrons being –vely charged and holes being +vely charged. The characteristic property of intrinsic semiconductors is that they possess neutralisation current i.e., number of electrons=no. of holes. As a result of this current intrinsic semiconductors have little current carrying capability, to enhance its conducting properties a mechanism needs to be modified in the case of intrinsic semiconductors, the property of enhancing the conductivity of semiconductors is called doping. The amount of doping should be moderate, semiconductors formed by intiating doping process is called extrinsic semiconductors.
The Essay on Type Semiconductor Electron Electrons Energy
Semiconductors have an electrical resistivity that is in between those of good conductors and those of good insulators. Both silicon and germanium, which are the two basic semiconductors, have four electrons in the outermost electron sub shell. In formation of the lattice structure of the silicon or germanium, all the valence electrons are involved in the bonding, so the material should be an ...
EXTRINSIC SEMICONDUCTORS:
The semiconductors present in impure form are called as extrinsic semiconductors. The impurities added to the semiconductor belongs to III and Vth group of the periodic table, the IIIrd group elements are trivalent impurities such as boron, aluminium, gallium, indium and Vth group elements are pentavalent impurities such as arsenic, antimony, phosphorous, bismuth. Silicon and germanium semiconductors are tetravalent in nature, when pentavelent impurity like phosphorous is added to silicon four valence electrons of silicon form covalent bond with four valence electrons of silicon, but one electron will lie free without participating in any bond the amount of energy required to dislodge this electron from the outermost valence shell is very small nearly of the order of 0.024 ev. Therefore by adding minute amount of impurity to semiconductor electrons are generated, hence these semiconductors are called n-type extrinsic semiconductors.On the other hand by adding trivalent impurities like boron to a semiconductor three valence electrons of silicon form covalent bond with three valence electrons of impure atom. Whereas one electron of semiconductor atom is electron deficient hence the semiconductor completes its bonding by stealing an electron from the neighbouring atom. However a vacancy is created by adding trivalent impurity, hence these impurities are called as acceptor impurities and semiconductors are called as p-type semiconductors
(a) P-type semiconductors
(b) N-type semiconductors
APPLICATIONS
1. Semiconducting materials play a pivotal role in electronic field because of its peculiar property of temperature coefficient of resistivity
The Term Paper on Semiconductors
... semiconductors: There are two types of semiconductors * Intrinsic semiconductors * Extrinsic semiconductors Intrinsic semiconductors: Intrinsic semiconductors are those semiconductors in which no impurity is added. For example silicon semiconductor containing all the silicon ... valence electrons of the impurity will form bond with the four valence electrons of the silicon atom and the fifth electron ...
2. Semiconducting principle can be utilised in the form of voltage regulator in zener diode where forward bias and reverse biasing action takes place
3. Rectifiers another class of semiconductors play a key role as an electronic device in the industry
4. Semiconducting materials are utilised in LED’s, Photodiodes as display devices.
