Physics 2 Marks Questions

(i) In the forward biased state of P-N junction, the width of the depletion layer decreases.
(ii) The depletion layer width increases in the reverse biased state of the P-N junction.

(i) In forward bias the thickness of the depletion layer decreases.
(ii) In reverse bias condition the thickness of the depletion layer increases.

Effect of temperature on semiconductors : When the temperature of semiconductors is increased, more electrons get excited by thermal energy and transition from valence band to conduction band. Hence more quantity holes are produced in. In this way, by increasing the temperature, conductivity increases due to increase in the number of charge carriers. The resistance temperature coefficient of semiconductors is negative. Semiconductors behave like insulators at absolute zero temperature.

When an external electric field is applied on a semiconductor, the charge carriers produce two types of currents :
(1) Drain current : This current flows from the external electric field of charge carriers. It arises as a result of movement along.
(2) Diffusion current : This current arises due to the movement of free charge carriers in a semiconductor from high concentration region to low concentration region.

Following are the examples of elemental semiconductor and compound semiconductor :
(i) Elemental semiconductors : Si and Ge
(ii) Compound semiconductors :
• Inorganic : CdS, GaAs, CdSe, InP etc.
• Organic anthracenes, doped phthalocyanates etc.
• Organic polymers : polypyrrole, polyaniline, polythiophene etc.