The electric field sweeps free carriers out of this region and hence it is called depletion region as it is depleted of free carriers.

Digital electronics deals with logical operations. The variables are called logical variables

Electric field is strong enough to break (or) rep tune the covalent bonds in the lattice and there by generating electron - hole pairs. This effect is called Zener effect.

The process in which alternating voltage or alternating current is converted direct voltage or direct current is called rectification.

If the positive terminal of the external voltage source is connected to the p-side and the negative terminal to the n-side, it is called forward bias.

The internal repulsion of the depletion layer stops further diffusion of free electrons across the junction. This difference in potential across the depletion layer is called barrier potential.

The energy gap between the valance band and conduction band is called forbidden energy gap

(i) De Morgan's First theorem states that the complement of the sum of two inputs is equal to the product of its complements.
\(\overline{\mathrm{A}+\mathrm{B}}=\overline{\mathrm{A}} \cdot \overline{\mathrm{B}}\)
(ii) The second theorem states that the complement of the product of two inputs is equal to the sum of its complements.
\(\overline{\mathrm{A} \cdot \mathrm{B}}=\overline{\mathrm{A}}+\overline{\mathrm{B}}\)

(i) If the portion of the output fed to the input is in phase with the input, then the magnitude of the input signal increases
(ii) It is necessary for sustained oscillations.

The leakage current is the current that the diode will leak when a reverse bias is applied to it.

When a PN junction diode is forward biased, the depletion region decreases and the diode conduct once after the barrier potential is crossed, when it is reverse biased the depletion region increases and the diode does not conduct sci it is called as unidirectional device.

The process of adding impurities to the instrinsic semiconductor is called doping.

S.No Intrinsic semiconductor Extrinsic semiconductor (i)  A semiconductor in its pure form without impurity is called an intrinsic
semiconductor. When small amount of impurity is doped in pure semiconductors it becomes extrinsic semiconductors.
  (ii) The number of free electrons in conduction band is almost equal to number of holes in valence band. The number of free electrons and holes is never equal. (iii) Electrical conductivity is a function of temperature along. Its electrical conductivity depends upon the temperature as well as on the quantity of impurity atoms doped the structure.

(i) In NPN transistor, a positive voltage is given to the collector terminal to produce a current flow from the collector to the emitter.
(ii) In a PNP transistor, a positive voltage is given to the emitter terminal to produce current flow from the emitter to collector.
(iii) To operate the transistor in the active region, emitter-base must be forward biased and collector base must be reverse biased.

A solar cell, also known as photovoltaic cell, works on the principle of photovoltaic effect Accordingly, the p-n junction of the solar cell generates emf when solar radiation falls on it. The construction details and cross-sectional view are shown in Figure.

(i) In a solar cell, electron-hole pairs are generated due to the absorption of light near the junction.
(ii) Then the charge carriers are separated due to the electric field of the depletion region.
(iii) Electrons move towards n-type Silicon and holes move towards p-type Silicon layer.
(iv) The electrons reaching the n-side are collected by the front contact and holes reaching p-side are collected by the back electrical contact. Thus a potential difference is developed across solar cell.
(v) When an external load is connected to the solar cell, photocurrent flows through the load.
(vi) Many solar cells are connected together either in series or in parallel combination to form solar panel.
(vii) Many solar panels are connected with each other to form solar arrays.
(viii) For high power applications, solar panels and solar arrays are used.
Applications:
(i) Solar cells are widely used in calculators, watches, toys, portable power supplies, etc.
(ii) Solar cells are used in satellites and space applications.
(iii) Solar panels are used for commercial production of electricity.