Advertisements
Advertisements
Question
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?
Solution
An electron jumps from the valence band to the conduction band only when it has gained sufficient energy. The thermal collisions sometimes do not provide sufficient energy to the electron to jump. Also, energy is lost in the form of heat because of the collision of the carriers with other charge carriers and atoms. Because of all these losses, only few electrons are left with sufficient energy to jump from the valence band to the conduction band. So, the population of electron in the conduction band does not keep on increasing with time.
APPEARS IN
RELATED QUESTIONS
Distinguish between a conductor and a semi conductor on the basis of energy band diagram
Draw separate energy band diagram for conductors, semiconductors and insulators and
label each of them.
Draw energy band diagrams of an n-type and p-type semiconductor at temperature T > 0 K. Mark the donor and acceptor energy levels with their energies.
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?
Electric conduction in a semiconductor takes place due to
An electric field is applied to a semiconductor. Let the number of charge carries be nand the average drift speed by v. If the temperature is increased,
Let np and ne be the number of holes and conduction electrons in an intrinsic semiconductor.
In a pure semiconductor, the number of conduction election 6 × 1019 per cubic metre. How many holes are there in a sample of size 1 cm × 1 mm?
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.)
Estimate the proportion of boron impurity which will increase the conductivity of a pure silicon sample by a factor of 100. Assume that each boron atom creates a hole and the concentration of holes in pure silicon at the same temperature is 7 × 1015 holes per cubic metre. Density of silicon 5 × 1028 atoms per cubic metre.
With reference to Semiconductor Physics,
Draw a labelled energy band diagram for a semiconductor.
What is forbidden band?
A window air conditioner is placed on a table inside a well-insulated apartment, plugged in and turned on. What happens to the average temperature of the apartment?
Two radioactive substances A and B have decay constants 3λ and λ respectively. At t = 0 they have the same number of nuclei. The ratio of the number of nuclei of A to those of B will be `1/"e"` after a time interval:
If the lattice constant of this semiconductor is decreased, then which of the following is correct?
In a common-base circuit calculate the change in the base current if that in the emitter current is αmA and a = 0.98
In a semiconductor, the forbidden energy gap between the valence, band and the conduction band is of the order of
Hole are majority charge carrier in
Which one of the following elements will require the highest energy to take out an electron from them?
Pb, Ge, C and Si
