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In any semiconductor (doped or not) vibrations of the atoms in the crystal can sometimes knock electrons out of the atom's valence band into the conduction band. When this happens the electron now in the conduction band is added to the population of electrons in the semiconductor, while the void it left behind in the valence band is added to the population of holes in the semiconductor. As the vibrations that cause this generation of electron and hole pairs are usually thermal (although there are other causes too) they are usually called thermally generated electrons and holes.
Since the electron and hole pair are in close proximity when formed, many of them recombine before they could be separated by an electric field in the crystal or by simple diffusion.
There is of course a somewhat more complicated (but also more correct) explanation using Quantum Mechanics, but the above is sufficient to understand it at the first approximationlevel.
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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 can't the potential barrier of a diode be used as a voltage source?
The potential barrier of a diode is caused by the movement of electrons to create holes. The electrons and holes create a potential barrier, but as this voltage will not supply current, it cannot be used as a voltage source.
Do both holes and electrons be regarded as the current producer?
No. They don't produce current, they only transport it.
Why intrinsic semiconductors are not used in practice for manufacturing of electronics devices?
The main reason semiconductor materials are so useful is that the behavior of a semiconductor can be easily manipulated by the addition of impurities, known as doping. Semiconductor conductivity can be controlled by introduction of an electric or magnetic field, by exposure to light or heat, or by mechanical deformation of a doped mono-crystalline grid; thus, semiconductors can make excellent sensors. Current conduction in a semiconductor occurs via mobile or "free"electrons and holes. collectively known as charge carriers. Doping a semiconductor such as silicon with a small amount of impurity atoms, such as phosphorus or boron. greatly increases the number of free electrons or holes within the semiconductor. It can be make in very small size and the electronics device are small in size that why the semiconductors are used in electronic devices. The above explains HOW semi conductors work. The reason for WHY they are used is, what's the alternative? The only alternative is thermionic valves (tubes). Tubes fell out of favour for many reasons. They run hot Made of glass and delicate, Heavy Large Consume lots of power Need high voltages. Semi conductors are the opposite of all of these.
Why TCR is negative for semiconductor and positive for metal?
Resistance decreases as more carriers are thermally generated with increased temperatures in a semiconductor. In metals there are plenty of carriers so the increase is negligible compared to the increased scattering off the lattice and impurities as temperature increases and therefore resistance increases with temperature.
What is avalanche break down?
When applied voltage is higher in reverse bias condition thermally generated electrons will rupture the bonds and increase the minority carriers
If a pure Si crystal has a million free electrons inside it how many holes does it have.what happens to the no of free electrons and holes if the ambient temperature increases?
If the crystal is pure Si (no dopants or impurities) then the number of free electrons in the conduction band will be equal to the number of holes in the valence band. Each electron leaves behind a hole when it is thermally excited into the conduction band. If the ambient temp. increases, there will be more thermal energy available which will increase both the number electrons and the number of holes.
How does a trans resistor work?
Wherever there is resistance or conductance and a current generated through interaction of electrons and holes there will be amplification. Trans-resistor is basically transfer of resistance.
Is iorn conductive?
Iron (Fe) is electrically and thermally conductive.Iron is a metal element. It has free electrons. So it is a good conductor of heat and electricity.
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.
What is the number of free electrons and holes in a pure semiconductor at 0k?
There are no free electrons and holes in a pure semiconductor at 0k.
How are electrons generated in a gas filled tube?
As this relates to EE, the electrons are already in there.
What happens to high energy electrons generated during Krebs cycle?
The cells do with all those high-energy electrons in carriers like NADH? in the presence of oxygen, those electrons can be used to generated huge amounts of ATP.
What is produced as electrons move from one carrier to the next?
the ATP generated
The machine that measures electric currents generated by neurons is called?
Electrons
How is electricity mostly generated?
it is because of passing of electrons in a wire or medium
What is the formula for mobility of electrons and holes?
E=uVd
