Addition of trivalent impurity to a semiconductor creates many:
Addition of trivalent impurity to a semiconductor creates many holes. A trivalent element has three electrons in its valence shell. It shares three electrons with three neighboring silicon atoms in the lattice, the fourth silicon atom demands an electron but the trivalent atom has no more electron to share. This creates a void in the lattice which we call it has a hole. Since the electron is deficient, the hole readily accepts an electron, this makes it a P-type (Positive type) extrinsic semiconductor.