I have a p-n junction diode(For simplifying,consider it as a stack of array of spherical atoms arranged in a cuboid of length L).Now divide the cuboid into 2 half cuboid each of length L/2 and this partition wil be p-n junction .Consider the event when depletion region is already formed.Now the atoms just touching the junction on one side will be positively charged(n region) and the other side will be negatively charged(p region).Suppose we have 2 or 3 layers of such atom each in both region.

Now my doubt is what we mean by width of depletion region? I know how an electric field is set up between two plates of charges but this condition is somewhat different as in each region we have something like,say, a rectangular box of positive charged atoms and similarly a box of negatives.I am unable to think of depletion width and so unable to visualize the extent of electric field in depletion region.Someone please help.