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Why fermi energy level is midway between conduction band and valence band in semiconductors?
Sarathy1991
To be exact EF should be at the valence band edge (EV) at 0K because no energy state above EV are occupied at 0K; however, for intrinsic semiconductors there are no states in the band gap anyway, so placing the EF anywhere in the band gap including conduction band edge does not add any states as being occupied. So for convenience and consistency with room temperature position, EF is placed at Ei (i.e. room temperature intrinsic Fermi level position).
Wiki User
∙ 14y ago
Wiki User
∙ 12y agoThe Fermi level moves to wherever it needs to be to assure that the overall
system is charge-neutral. In an n-type semiconductor, we introduce fixed
positive charges (donors), which must be balanced by mobile negative charges
(electrons). The excess electrons must reside in the conduction bands,
because the valence bands are full. To have excess electrons in the
conduction band, the Fermi level (electrochemical potential for electrons)
must lie near the conduction band. A similar argument can be made for
p-type doping
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Why does a semiconductor have fewer electrons than a conductor?
Valence electrons only are able to cross the energy gap in semiconductors since it is greater than that of conductors. That is why semiconductors have fewer free electrons than conductors.
What is the difference between conduction convection and thermal energy?
Conduction and convection are two ways in which thermal energy is transferred, the third way is by radiation.
According to band theory mg is an insulator while in practice it is a conductor why?
According to band theory , the energy gap between valence band and conduction band was high. But during heating the energy gap get decreased. this is the reason why the mg behaves as an conductor.
What is the name of two energy bands at which current is produced in silicon?
The two energy bands in which current is produced in Silicon (type of intrinsic semiconductor) are VALENCE BAND & CONDUCTION BAND
What is the transfer of energy when molecules bump into each other through contact?
The energy that is transferred when molecules bump into each other is called conduction. Conduction is the transfer of heat energy between substances that are in direct contact with each other.
Why in intrinsic semiconductors do you need to apply very high potential to transfer electrons from the valence band to the conduction band?
Semiconductors, in the absence of applied electric fields, act a lot like insulators. In these materials, the conduction band and the valence band do not overlap. That's why they insulate. And that's why you have to apply some serious voltage to them to shove the valence electrons across the gap between the valence and conduction bands of these semiconductor materials. Remember that in insulators, there is a "band gap" between the lowest Fermi energy level necessary to support conduction and the highest Fermi energy level of the valence electrons. Same with the semi's. In metals, the conduction band overlaps the valence band Fermi energy levels. Zap! Conductivity.
Do semiconductor material have a very high resistance at room temperature?
No. As temperature increases, resistance of semiconductors decrease. This is because semiconductors have a small energy gap between their valence band and conduction band (in the order of 1 eV). Electrons must exist in the conduction band in order for the material to conduct but electrons exist in the valence band naturally. The electrons gain thermal energy for surroundings and jumps the energy gap from valence band to conduction band and hence, the SC material more readily conducts. As temperature increases, electrons can gain more thermal energy, more electrons can enter the conduction band and hence, resistance decreases.
Why does a semiconductors ability to conduct electricity increase when temperature rises?
if we increase the temp so large no of electrons jumbs from valence energy band to conduction energy band .when there are alarge no of electrons in conduction band to the conduction increase means this simiconductor can conduct easyly. thanx Engr Bashir Khan.
What are conduction?
The quantum mechanical energy band where electrons reside in semiconductors that participate in electrical conduction.
What are conduction band?
The quantum mechanical energy band where electrons reside in semiconductors that participate in electrical conduction.
What is the difference between direct and indirect energy?
The band gap represents the minimum energy difference between the top of the valence band and the bottom of the conduction band, However, the top of the valence band and the bottom of the conduction band are not generally at the same value of the electron momentum. In a direct band gap semiconductor, the top of the valence band and the bottom of the conduction band occur at the same value of momentum.In an indirect band gap semiconductor, the maximum energy of the valence band occurs at a different value of momentum to the minimum in the conduction band energy
What makes silicon a semiconductor?
Elements have two bands. One is Valence band and other is Conduction band. Valence band contains electrons whereas the conduction band is empty. The energy gap between them is called the forbidden gap. In case of metals, this gap is very small or the bands overlap. Therefore, the electrons are able to jump from the valence band to the conduction band and hence metal are able to conduct electricity and they are generally conductors. In case of Non-Metals, the energy gap is very large and hence hence electrons are not able to move from valence band to conduction band. Hence they are insulators. But in case of elements like Silicon, Germanium this gap is between Metals and Non-Metals, hence few electrons are able to move from valence band to conduction band. Therefore they have some conductivity but it is low and hence they are called semiconductors.
What are the conditions for the fermi level to be exactly in the middle of the energy band gap of a semiconductor material?
For intrinsic semiconductors like silicon and germanium, the Fermi level is essentially halfway between the valence and conduction bands. You don't have to do anything; just keep the semiconductor intrinsic!
What is the difference between the resistance of conductor and insulator?
Conductors allow most, if not all, electricity to pass through it. This is due to "wandering electrons" that aren't tightly bound to the nucleus of the conductor itself.Resistors conduct some, but not all electricity to pass. It somewhat resists it, hence resistors.Insulators do not allow electricity to pass through it due to the electrons being so tightly bound to the nucleus.
What are valence band?
The quantum mechanical energy band where electrons reside in semiconductors that participate in interatomic bonding.
Why the breakdown voltage of silicon is 0.7V whereas for germanium it is 0.3V?
because germanium has lower energy gap between conduction and valence bands
Why conduction band and valence band partially filled?
No. Conduction band is basically the unfilled energy levels into which electrons can be excited to provide conductivity.
