Advertisements
Advertisements
प्रश्न
With reference to semiconductor physics, answer the following question.
In which material “Forbidden band” is absent?
उत्तर
In the case of a conductor, there is no forbidden gap between the two bands; instead, they overlap. This permits unrestricted electron conduction at all energies, which is a characteristic of conductors.
APPEARS IN
संबंधित प्रश्न
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?
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?
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,
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,
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?
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.
A semiconducting material has a band gap of 1 eV. Acceptor impurities are doped into it which create acceptor levels 1 meV above the valence band. Assume that the transition from one energy level to the other is almost forbidden if kT is less than 1/50 of the energy gap. Also if kT is more than twice the gap, the upper levels have maximum population. The temperature of the semiconductor is increased from 0 K. The concentration of the holes increases with temperature and after a certain temperature it becomes approximately constant. As the temperature is further increased, the hole concentration again starts increasing at a certain temperature. Find the order of the temperature range in which the hole concentration remains approximately constant.
(Use Planck constant h = 4.14 × 10-15 eV-s, Boltzmann constant k = 8·62 × 10-5 eV/K.)
An n-type semiconductor is
In a common-base circuit calculate the change in the base current if that in the emitter current is αmA and a = 0.98
- 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.