A p-type crystal is formed when Ge or SI crystal is doped with an impurity which is:

Explanation

A p-type crystal is formed when a semiconductor crystal, such as Germanium (Ge) or Silicon (Si), is doped with an impurity that has one less valence electron than the atoms of the crystal. This impurity is known as a "trivalent" impurity. When a trivalent impurity is added to the crystal lattice, it replaces some of the original atoms, creating "holes" or vacant spaces in the crystal's valence band. These holes act as positive charge carriers. The trivalent impurity donates one of its valence electrons to the crystal, creating a positively charged "dopant" ion and leaving behind a vacant spot in the crystal structure. This addition of trivalent impurities effectively increases the concentration of positively charged holes in the crystal lattice, creating a surplus of positive charge carriers and hence leading to the formation of a p-type semiconductor.