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In an intrinsic semiconductor, a few electrons get thermally excited and break from their valence bond to become a free electron. This leaves behind a vacancy in its place called 'hole'.
In a P-type semiconductor, B with 3 electrons replaces a Si atom with 4 electrons in the lattice. 3 covalent bonds are formed by B with 3 neighbouring Si. But there is a deficiency of one electron in B for bonding with the 4th Si. This deficiency/vacancy is called a hole.
When an electric potential difference is present, the electrons from adjacent valence bond moves into the vacancy near it while moving along the potential.
The following represents the movement of valence electron.
Terminology:
* represents valence electron
_ represents hole
A is -ve and B is +ve.
..I A * * * _ * * * B
.II A * * _ * * * * B
III A * _ * * * * * B
.IV A _ * * * * * * B
I- Hole is at the 4th position.
II- At first, the 3rd electron from left shifts right to fill the vacancy and leaves behind a vacancy in its place. The vacancy is at the 3rd position.
III- Next, the 2nd electron from left has shifted to the 3rd place and filled up that vacancy but leaves a vacancy at its place. The vacancy is at 2nd position.
IV- Now, the 1st electron from left moves to occupy the vacancy at the 2nd position creating another vacancy in its own place. The vacancy is at 1st position.
As the electrons moved right, the vacancy moved left. The vacancy is called a hole (just a shorter name for convenience). The movement of holes is really the movement of electron in the valence band. Therefore, the mobility of a hole is indirectly the mobility of valence electrons.
Mobility is the velocity acquired per unit electric field.
In the intrinsic and N type semiconductors, many free electrons are present i.e. electrons in conduction band which are free to move in the crystal as against valence electrons which can only move in the lattice points.
When an electric field is applied, both the valence electrons and the free electrons move in the same direction. The hole direction is opposite to that of valence electron but the mobility is the same, as explained earlier.
Even for the same electric field, valence electrons cannot move as freely as the free electrons because its movement is restricted. Therefore, the velocity of valence electrons is less compared to free electrons. In other words, the velocity of holes is less compared to free electrons. This means mobility is also less for a hole compared to free electron.
Thus, mobility of a free-electron (often abbreviated as 'electron') is greater than that of a hole (indirectly referring to valence electron).
Electrons can jump from valence shell to valence shell, or from hole to hole. Holes, which are actually atoms missing an electron in their valence shell, are locked in the lattice structure of the material that they are contained within. Holes are, in reality, a theoretical concept used to explain current flow - it is generally accepted by most main stream physicists today that current flow is electron flow - but the concept of hole flow allows some of the mathematics to be easier to deal with, i.e. without those nagging minus signs.
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Why mobility of holes is greater than mobility of electron?
electrons have less effective size than that of holes(which actually are not real)...formula says m(mobility)=drift velocity/electric field=et/m where t is relaxation time.. so mobility is inversely proportional to mass hence e has more mobility.
Why are germaninum diodes popular than silicon diodes?
because in Ge mobility of both electrons and holes is higher than the corresponding carriers in Si....and second reason -Ge can be refined and processed more easily..
Why are npn transistors used more often than pnp transistors?
The primary reason that NPN transistors are used more often than PNP transistors is that they usually operate faster (at higher frequencies) because the mobility of the current carriers in NPN transistors (electrons) is much higher than that of the current carriers in PNP transistors (holes).
Are the similarities between the UJT and BJT?
PNPOperates on minority charge carriers (holes).Slower than NPN because holes are less mobile than electrons.Slightly easier to manufacture than NPN.More sensitive to high temperature due to thermal hole generation.etc.NPNOperates on minority charge carriers (electrons).Faster than PNP because electrons are more mobile than holes.Slightly harder to manufacture than PNP.Less sensitive to high temperature.etc.
How do you Define the mobilty of charge carrier?
I am assuming the charge carries are electron and hole in an semiconductor. the mobility of charge carriers can be understood as the easy with which the carrier can move in a semiconductor. the mobility depends on many factors like the semiconductor material (because of the crystal structure), semiconductor specimen temperature, the effective mass of carrier, the applied electric field across the specimen. in general if we compare the mobility of electron with hole in a silicon semiconductor, the mobility values at room temperature is some thing around 1350 cm^2 per volt sec and 450 cm^2 per volt sec for electron and holes. that is mobility of electron is 2-3 time more than the holes in silicon.
Which has greater mobility in intrinsic semiconductor Electrons or holes?
The mobility of electrons is always greater than holes. Only the number of electrons and holes would be same in an intrinsic semiconductor.
Why mobility of holes is greater than mobility of electron?
electrons have less effective size than that of holes(which actually are not real)...formula says m(mobility)=drift velocity/electric field=et/m where t is relaxation time.. so mobility is inversely proportional to mass hence e has more mobility.
Why are germaninum diodes popular than silicon diodes?
because in Ge mobility of both electrons and holes is higher than the corresponding carriers in Si....and second reason -Ge can be refined and processed more easily..
Why npn transistor are more using than pnp transistor. Give two reasons?
1. NPN transistors current conductin is by electrons and conventional current flow will be in the opposite direction. 2. Majority charge carriers are electrons whose mobility is almost double than that of holes.
How does the energy of the core electrons compare with the energy of valence electrons?
The energy of the valence electrons is greater than the energy of the core electrons.
What is found with the neutrons and have a greater mass than electrons?
protons
Why mobility of electrone is larger than hole?
I may be wrong but...Holes don't exist - they are a nice way of describing electron movement but it's just a mathematical and descriptive term. Electrons do the actual moving Holes are just a way of talking baout electron movement.Electrons don't really exist either but that's getting a bit far into the physics.
What is the speed of electrons compara to holes?
Electrons typically move faster than holes in a semiconductor material. This is because electrons are negatively charged and can move freely through the material, while holes, which are essentially the absence of an electron, move more slowly as they are positively charged and rely on electron movement to migrate.
How many outer electrons do most nonmetals have?
Greater than 3
Why is collector region is greater than emitter region?
the collector is where we are getting the the holes or electrons from the emiiter through the base (wrt to the transistor we use). As the carriers are collected there,most heat is dissipited there. so it must be of large size
Which subatomic particle has a greater mass a proton or an electron?
A proton has a greater mass than an electron. Protons are about 1,836 times more massive than electrons.
Why does the n p n works better than the p n p in basic electronics .?
No. of electrons are more than holes
