Question

explain :

1} why is the current in the reverse bias almost independent of the applied potential upto a critical voltage ?

2} why does the reverse current show a sudden increase at the critical voltage ?

Answer 1

(i) In reverse bias of p-n junction diode the small current is due to minority carrier and hence
resistance is also very high so very large increase in voltage leads to a very-very small increase in
reverse bias currents so we conclude that in reverse bias reverse current almost independent of
applied potential upto a critical voltage because after this critical voltage current increase suddenly

(ii) In reverse bias reverse current through junction diode is due to minority carries. As reverse bias
voltage is increased electric field at function becomes significant. When reverse bias voltage becomes
equal to zener voltage, electric field strength across function becomes high. Electric field across
function is sufficient to pull valance electron from the host atom on p-side & accelerate them towards
n-side. The movement of these electrons across the function account for high current which is observed
at break down reverse voltage.