Question

In a p–n junction a potential barrier of 300 meV exists across the junction. A hole with a kinetic energy of 400 meV approaches the junction. The K.E of the hole when it crosses the junction (i) from p to n–side and (ii) from n to p–side will be

(1) 100 eV, 700 eV

(2) 100 eV, 100 eV

(3) 700 eV, 700 eV

(4) 700 eV, 100 eV

Answer 1

(1) 100 eV, 700 eV

The p–region is at a lower potential than n–region in depletion layer when hole crosses depletion layer from n– to p–side; it (hole) is accelelrated. Therefore 

K = Kinetic energy of hole

When hole crosses depletion layer from p– to n–side, it is retarded. Therefore 

K’ = Ke – |e| V 

= (400–300) meV = 100 meV

The correction choice is (1)