RRB Technician Grade 1 Model Paper 4

Concept:The space charge region, also known as the depletion region, is completely depleted of mobile charge carriers.Explanation:At a p-n junction, free electrons from the $n$-side diffuse into the $p$-side and recombine with holes there.Similarly, holes from the $p$-side diffuse into the $n$-side and recombine with free electrons there.This diffusion and recombination leaves behind immobile charged ions near the junction.On the $n$-side, positively charged donor ions are left behind.On the $p$-side, negatively charged acceptor ions are left behind.These fixed ions form the space charge region, which is also called the depletion region.Since the free electrons and holes have recombined, this region contains no mobile carriers.Thus, only immobile ions exist in this region.Answer:Option A: The space charge region around a p-n junction does not contain mobile carriers.