Draw and discuss volt-ampere characteristics of a tunnel diode.

Ans:  Volt-ampere characteristics of a tunnel diode: The V-I characteristics of a tunnel diode are shown in fig. (a) Forward bias produces immediate conduction as soon as forward bias is applied, significant current is produced.  Current attains quickly its peak value I_p, when applied forward bias attains a value of  V_p volts. Current variation in the vicinity  of  origin  is  because of quantum  mechanical  tunneling  of  electrons  through  narrow space  charge  region  of  the  junction.  With  further  increase  in  forward  voltage,  diode current starts decreasing till it attains its minimum value, called valley current Iv corresponding to valley voltage Vv. Hence from peak point A to valley point B the diode current falls with increase in voltage resulting in negative resistance in this region. ACTUALLY this portion A B of the characteristic constitutes the most useful property of diode. In  this  region  diode,  rather than absorbing  power,  produces  power.   So  tunnel diode can be used as a very high frequency oscillator. For voltages higher than valley voltage V_v current starts increasing as in any normal diode.