Illustrate the polarity of Barrier potential.

The  free  electrons  which  cross  over  the  junction  recombine  with  the holes of p-type and uncover some of the negative acceptor ions as shown in fig. 13(b) This establishes a negative charge on the p-side of the junction. This process of diffusion continues till a sufficient number of donor and acceptor impurity ions are uncovered and establish  a  requisite  potential  difference  (i.e.  nearly  0.3  V  in  case  the  pn  junction  is formed of germanium semiconductor and 0.7 V for silicon pn junction). Afterwards, further diffusion is prevented because now positive charge  on n-side repels holes to cross from p-type to n-type and negative charge on p-side repels free electrons to enter from n-type to p-type. Hence a potential difference created across the junction acts as a barrier that restricts further movement  of charge  carriers  i.e.  holes  and  electrons.   This  is known as a Junction Barrier or Potential Barrier V_o