Question

The potential barrier, in the depletion layer, is due to:
(A) Electrons
(B) Holes
(C) Ions
(D) Forbidden band

Answer 1

We need to define a depletion layer. The depletion region is so named because it is formed from a conducting region by removal of all free charge carriers, leaving none to carry a current. State the carriers of change, which are depleted in the layer.

Complete step by step solution:
In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region, space charge region or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have been diffused away, or have been forced away by an electric field. The only elements left in the depletion region are ionized donor or acceptor impurities.
The depletion region is so named because it is formed from a conducting region by removal of all free charge carriers, leaving none to carry a current.
The depletion layer is the region at the junction of a diode which is devoid of ions. Therefore the potential barrier in the depletion layer is due to ions.
The correct answer is Option A.

Note:
Electrons and holes diffuse from regions of higher concentrations to regions of lower concentrations, until they are uniformly distributed.
By definition, the N-type semiconductor has an excess of free electrons (in the conduction band) compared to the P-type semiconductor, and the P-type has an excess of holes (in the valence band) compared to the N-type.
Therefore, when N-doped and P-doped semiconductors are placed together to form a junction, free electrons in the N-side conduction band migrate (diffuse) into the P-side conduction band, and holes in the P-side valence band migrate into the N-side valence band.
Following transfer, the diffused electrons come into contact with holes and are eliminated by recombination in the P-side. Likewise, the diffused holes are recombined with free electrons so eliminated in the N-side. The net result is that the diffused electrons and holes are gone. As a result, majority charge carriers (free electrons for the N-type semiconductor, and holes for the P-type semiconductor) are depleted in the region around the junction interface, so this region is called the depletion region or depletion zone.
Due to the majority charge carrier diffusion described above, the depletion region is charged; the N-side of it is positively charged and the P-side of it is negatively charged. This creates an electric field that provides a force opposing the charge diffusion. When the electric field is sufficiently strong to cease further diffusion of holes and electrons, the depletion region reaches equilibrium. Integrating the electric field across the depletion region determines what is called the built-in voltage (also called the junction voltage or barrier voltage or contact potential).