RBSE Class 12 Physics Notes Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits

These comprehensive RBSE Class 12 Physics Notes Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits will give a brief overview of all the concepts.

RBSE Class 12 Physics Chapter 14 Notes Semiconductor Electronics: Materials, Devices and Simple Circuits

Solids:
On the relative value of σ and ρ, the solids can be divided into following categories :
(i) Metals are those materials which have low resistivity (ρ) and high conductivity (σ).
Value of ρ is between 10^-2 to 10^-8 Ωm
Value of σ is between 10² to 10⁸ Sm^-1

(ii) Insulators are those materials which have high value of ρ and low value of σ.
Value of ρ is between 10¹¹ to 10¹⁹ Ωm.
Value of σ is between 10^-11 to 10^-19 Sm^-1

(iii) Semiconductors are those materials which have values of ρ and σ intermediate to metals and insulators.
Value of ρ is between 10^-5 to 10^-6 Ωm
Value of σ is between 10⁵ to 10^-6 Sm^-1

Energy band in solids:
In single free atom, electrons have defined energy level, but a solid crystal contains about 1023 atoms/ cm3. So each atom is in the electrostatic field of neighbouring atoms and due to interaction between the atoms, the modification of energy level takes place. This broadening of energy level is called energy band.

Fermi Energy:
Fermi Energy is the maximum possible energy possessed by free electrons of a material at 0 K.

Intrinsic semiconductor:
Intrinsic semiconductor is a pure semiconductor which is free of every impurity. At 0 K it is an insulator. On increasing its temperature, some covalent bonds break away and release the electrons. The minimum energy required to break a covalent bond is 0.7 eV for Ge and 1.1 eV for Si. These electrons move to conduction band leaving behind empty space or vacancy left in the bond called a hole. The number density of electron and hole is equal
i.e. n_e = n_h = n_i
where n_i is the number density of intrinsic carriers (electrons and holes) in a pure semiconductor.

Doping:
It is the process of addition of a desired impurity in an intrinsic semiconductor to modify its properties. The impurity atom is called dopant. And a doped semiconductor is called extrinsic semi-conductor.

Extrinsic semiconductor:
A doped semi-conductor with a suitable impurity to increase its conductivity is called extrinsic semiconductor. Extrinsic semiconductors are of two types.

• n-type semiconductors are those extrinsic semiconductors in which pentavalent impurity (i.e. atoms having 5 valence electrons) like Sb or As is added to the pure semiconductor (intrinsic semi-conductor) to produce excess of elements (majority carriers).
• p-type semiconductors are those extrinsic semiconductors in which trivalent impurity (i.e. atoms having 3 valence electrons) like In or Ga is added to the pure (intrinsic) semiconductor to produce excess of hole (majority carriers).

Electrical conductivity of extrinsic semiconductor is given by
σ = \(\frac{1}{\rho}\) = e (n_eμ_e + n_hμ_h)
where μ_e = \(\frac{v_e}{\mathrm{E}}\) and μ_h = \(\frac{v_h}{\mathrm{E}}\) is called the mobility of electrons and holes respectively and ng and nh is the number density of electrons and holes respectively.

Energy Gap:
The energy gap E_g in a semiconductor depends upon the temperature of the semiconductor.
At room temperature (300 K)
For Ge, E_g = 0.72 eV
and for Si, E_g = 1.1 eV.