1) Trivalent impurity is added to a pure semiconductor it is called P-type semiconductor. 2) Some trivalent impurities are gallium , indium ,boron, aluminium etc. These impurities provide large number of holes.threrefore they are called acceptor impurities. 3) Above diagram is of p-type of semiconductor .Consider a pure Germanium crystal , it has four valance electrons which forms covalent bonds. 4) When gallium is added out of four electrons of Ge only three forms the covalent bonds with creating one hole as shown above. 5) The current in it is predominantly by holes(positive charge)So they are called as majority carriers and electrons are called minority charge carriers.