Which of the following accounts for the presence of the potential barrier in the depletion layer?a.Electronsb.Holesc.Forbidden bandd.a.     Ions

The potential barrier in the depletion layer of a semiconductor diode is primarily due to the ions. When a diode is formed by joining a p-type and n-type semiconductor, the free electrons from the n-type region begin to recombine with the holes in the p-type region. This recombination results in the formation of a region devoid of charge carriers, known as the depletion region.

The ions left behind in the depletion region create an electric field, which opposes the movement of electrons from the n-type region to the p-type region, and holes in the opposite direction. This electric field, or potential barrier, must be overcome by an external voltage to allow current to flow through the diode.

So, the correct answer is d. Ions.