Advertisements
Advertisements
प्रश्न
When an electron goes from the valence band to the conduction band in silicon, its energy is increased by 1.1 eV. The average energy exchanged in a thermal collision is of the order of kT which is only 0.026 eV at room temperature. How is a thermal collision able to take some to the electrons from the valence band to the conduction band?
उत्तर
Fermi level: it is the energy level occupied by the highest energy electron.
In an extrinsic semiconductor for example in n-type semiconductor, fermi level lies close to the conduction band so it needs a very small amount of energy to excite the electron from fermi level to conduction band. This energy is comparable to the thermal excitation energy. So even at room temperature,these semiconductors can conduct.For a p-type semiconductor, fermi level lies close to valence bane because here conduction takes place majorly via holes.So by the thermal excitation,a bond is broken and an electron hole pair is created.Out of this,hole comes to the valence band for conduction or equivalently an electron goes to the conduction band. In an intrinsic semiconductor, no impurity is doped so fermi level lies at the centre of band gap. Here only few electrons get sufficient energy via repeated thermal collisions to jump from the fermi level to the conduction band.Hence the conductivity of intrinsic semiconductor is less as compared to extrinsic semiconductor.
APPEARS IN
संबंधित प्रश्न
Distinguish between a conductor and a semi conductor on the basis of energy band diagram
Draw the necessary energy band diagrams to distinguish between conductors, semiconductors and insulators.
How does the change in temperature affect the behaviour of these materials ? Explain briefly.
Draw separate energy band diagram for conductors, semiconductors and insulators and
label each of them.
There are energy bands in a solid. Do we have really continuous energy variation in a band ro do we have very closely spaced but still discrete energy levels?
In semiconductors, thermal collisions are responsible for taking a valence electron to the conduction band. Why does the number of conduction electrons not go on increasing with time as thermal collisions continuously take place?
What is the resistance of an intrinsic semiconductor at 0 K?
When an impurity is doped into an intrinsic semiconductor, the conductivity of the semiconductor
An incomplete sentence about transistors is given below:
The emitter−..... junction is __ and the collector−..... junction is __. The appropriate words for the dotted empty positions are, respectively,
The impurity atoms with which pure silicon may be doped to make it a p-type semiconductor are those of
(a) phosphorus
(b) boron
(c) antimony
(d) aluminium.
Suppose the energy liberated in the recombination of a hole-electron pair is converted into electromagnetic radiation. If the maximum wavelength emitted is 820 nm, what is the band gap?
(Use Planck constant h = 4.14 × 10-15 eV-s, Boltzmann constant k = 8·62 × 10-5 eV/K.)
Find the maximum wavelength of electromagnetic radiation which can create a hole-electron pair in germanium. The band gap in germanium is 0.65 eV.
(Use Planck constant h = 4.14 × 10-15 eV-s, Boltzmann constant k = 8·62 × 10-5 eV/K.)
Let ΔE denote the energy gap between the valence band and the conduction band. The population of conduction electrons (and of the holes) is roughly proportional to e−ΔE/2kT. Find the ratio of the concentration of conduction electrons in diamond to the in silicon at room temperature 300 K. ΔE for silicon is 1.1 eV and for diamond is 6.1 eV. How many conduction electrons are likely to be in one cubic metre of diamond?
The energy of a hydrogen atom in the ground state is −13.6 eV. The energy of a He+ ion in the first excited state will be:
A hole in a. p – type semiconductor is
In a common base configuration Ie = 1 mA α = 0.95 the value of base current is
The reaction between α and β parameter of a transistor is given by
Hole are majority charge carrier in
Three photo diodes D1, D2 and D3 are made of semiconductors having band gaps of 2.5 eV, 2 eV and 3 eV, respectively. Which 0 ones will be able to detect light of wavelength 6000 Å?
- Assertion (A): In insulators, the forbidden gap is very large.
- Reason (R): The valence electrons in an atom of an insulator are very tightly bound to the nucleus.
Which one of the following elements will require the highest energy to take out an electron from them?
Pb, Ge, C and Si
