acceptor
/ ak-SEP-ter /
Picture again silicon's four-handed atoms, every hand clasped with a neighbor. This time drop in an atom with only three hands, like boron. It can hold three neighbors fine, but the fourth bond is left with a missing hand — an empty place where an electron ought to be.
An acceptor is an impurity atom that has one fewer outer electron than the host needs, so it readily accepts an electron from a nearby bond to complete itself. When it grabs that electron, the gap it leaves elsewhere is a hole — a vacancy that behaves like a positively charged particle free to move through the crystal. As neighboring electrons hop in to fill the gap, the hole effectively drifts in the opposite direction, carrying current.
Acceptors are how engineers add mobile holes on purpose, producing a p-type semiconductor (p for positive). The common confusion is to picture the hole as a literal floating positive object. It is not a particle in the usual sense; it is the collective effect of many electrons shuffling to fill an empty bond — a remarkably useful bookkeeping idea that turns out to be physically real in how it moves and responds to fields.
Boron is the classic acceptor in silicon: it has three outer electrons against silicon's four, so each boron atom leaves one bond short and creates a mobile hole. Doping silicon with boron makes it p-type.
Group-III atoms like boron each leave one empty bond — a hole — in silicon.
An acceptor, once it captures an electron, becomes a fixed negative ion in the lattice — yet the material stays neutral overall, because that negative ion is balanced by the positive hole it set free to move.