Q. What is a diode ?
A. The diode consists of two electrodes one is cathode and another is anode. The cathode emits electrons and the anode will attracts the emitted electrons when it is supplied by positive potential
Q. What is energy gap ?
A. The gap between conduction band and the valency band is called Energy Gap.To move the electrons from the valency band to conduction band the supplied external voltage must be equal to energy gap.
Q. What is valency band ?
A. The range of energy which is possessed by valency electrons is known as valency band.Here the electrons which are situated at outer most orbits are called valency electrons.The valency band consists of valency electrons which are having highest energy.
Q. What is conduction band ?
A. The range of energies possessed by a conducting electrons is known as conduction band.the conduction electrons are responsible for the conduction of current in a conducting material. So , these electrons are called as conduction electrons.
Q. How many types of solid materials are there and what are those materials?
A. Based on the energy gap the solid materials are classified into 3 types they are : conductors , insulators and semiconductors.
Q. What is a conductor ?
A. Those substances whose atoms have their outermost orbits incomplete are known as conductors(ex:Sodium , 1s2 2s2 2p6 3s1 ).In these conductors the valency electrons are very closely bounded to the nucleus and hence they can easily move from valency band to conduction band.so, the energy gap is very less or zero.
Q. What is insulator ?
A. Those substances which have more and more energy gap between valency and conduction band they are called insulators.In these materials the valency electrons are very lightly bounded to nucleus.
Q. What are Semi conductors ?
A. Those substances which have conductivity and resistivity properties in between conductors and insulators are called semi conductors.(ex : Si , Ge).Energy gap of these semiconductors lies between 0.5 to 1.1 eV.(For Ge it is 0.5 – 0.7eV ).
Q. How many types of semi conductors are there ?
A. Two types of semi conductors are there :
(1) Intrinsic or pure semiconductors.
(2) Extrinsic or impure semiconductors.
Q. What is an intrinsic semi conductor ?
A. Intrinsic semi conductor is a pure semiconductor.In these semi conductors if the temperature increases then the conductivity is also increases.At higher temperatures due to collisions some electrons absorb energy and raises to conduction band then in their places in valency band holes are created.
** In intrinsic semiconductor number of holes are equal to number of electrons.
Q. What is Fermi energy level ?
A. The average energy of charge carriers is calculated by Fermi energy level.
In pure semi conductors Fermi energy level is at the center of the valency and conduction bands.
In P-type semi conductors Fermi energy level is near to the valency band.
In N-type semi conductors Fermi energy level is near to the conduction band.