Question

Why are charge carriers absent in the depletion region?

Answer 1

Depletion region is a region observed in any semiconductor be it conductive or doped where the conductive species interact in such a manner that they diffuse towards each other adjoining the conducting and valence band of the semiconductor.

Complete answer:
A semiconductor conducts electricity using the interaction between electron holes (positive charge carrier) and free electrons (negative charge carriers) present on different sides of the semiconductor. Any typical semiconductor would contain the above-mentioned carriers which allow the transition/movement of electrons which in turn is responsible for its conductive properties.
In the case of a doped semiconductor, it is even more clear to observe this because there is a segregation/division of an N-type (conducts using free electrons and is negatively charged) and a P-type semiconductor (conducts using electron holes or electron voids and is positively charged). The diffused.
The depletion layer is formed when the holes and free electrons diffuse against each other, thereby forming a layer consisting of electron holes filled with free electrons. This is a repeated cycle as electrons travel via this region. Since both types of charge carriers interact in this region, they nullify/cancel out each other’s charges, thus making this layer almost chargeless or neutral. These carriers are hence, occupied or absent since they combine with each other losing their charge carrying identity.
This is the reason why charge carriers are found to be absent in the depletion region of a semiconductor.

Note: The above-mentioned case of nullifying of charges is only applicable when both the N-type and P-type parts of the semiconductors are equally conductive. If either of them is stronger than their counterpart, they would outweigh the number of carriers than the other causing a minute presence of charge carriers in the depletion region which could go undetected at times.