Draw the energy band diagrams of a tunnel diode for different biasing conditions.

Band  Diagrams  of  a  Tunnel  diode:   The  energy  band  diagram  for  a  heavily  doped unbiased P-N junction is shown in fig. 10(a) Note that the depletion region is very narrow and  the  filled  levels  on  the  N-side  are  exactly  opposite  those  on  the  P-side.   In  this condition,  no  tunneling  occurs,  as  there  are  no  empty  lower  energy  levels  to  which electrons from either side might cross the depletion region. It's also to be noted that conduction and valence bands on p- side are (negatively) higher than those on the n side, this is because of the formation of depletion region and barrier potential as a result of electrons  crossed  from  n-region  to  the  p-region.  N-region  has  lost  negative charge and p-region has gained them.