If a trivalent impurity (for instance, Boron, Aluminium) is incorporated into an intrinsic semiconductor then it will, in turn, produce a more significant amount of holes on the valence band. Such types of semiconductors are called P-type semiconductors. When a trivalent impurity is introduced in a semiconductor, one of its three valence electrons makes covalent bonds with three neigh... https://www.campuscomponent.com/blogs/post/difference-between-p-type-and-n-type-semiconductors