most probably u want to know why depletion region penetrates more into lightly doped side.

u know in depletion region there are two sides, N-side contains positive and P-side contains negative ions. and an important fact is that the number of ions will be equal in both sides.

now consider the situation of lightly doped semiconductor- there will be less carriers in a particular area than a highly doped semiconductor. so in order to have equal number of ions in the depletion region of the lightly doped site, the region has to penetrate more in the lightly doped semiconductor.

if i am wrong in predicting your question then sorry......