Question

(i) How does potential barrier of a semiconductor vary with temperature? 

(ii) What is LED? Name the two materials used in making LED, whose light falls in the visible region. Why LED is a better choice than a bulb in torch?

Answer 1

(i). The barrier potential of a semi- conductor increases with rise in temperature.

The barrier potential (V_B)of a semi-conductor is directly proportional to temperature in kelvin(T). 

The relation between V_B and T K in terms of the hole concentration on either side of the junction is given by :

V_B = \(\frac{K_BT}{q}log_e(P_p/p_n)\)

Where KB = Boltzmann constant, 

P_p = hole concentration in P-side 

P_n = hole concentration in n- side.

(ii). LED stands for light emitting diode. It is a heavily doped p-n junction diode which under forward bias emits spontaneous radiation, due to recombination of minority carriers on either side of the junction with majority carriers there. 

I -V characteristics of LED :

The following materials are used in making LEDs whose light falls in the visible region : 

(a) Gallium- phosphide(Gap)- giving red or green light 

(b) Gallium- arsenide-phosphide (GaAsp) - giving red or yellow light. 

LEDs are better than conventional bulb as the torch because LED is handy and light. It gives intense light and consumes less power.