acceptorimpure

An acceptor impurity, or acceptor dopant, is a foreign atom introduced into a semiconductor that creates an acceptor energy level within the material's band gap. Such impurities tend to accept electrons from the valence band, producing holes that act as mobile positive charge carriers. As a result, materials doped with acceptors exhibit p-type conductivity, where holes are the majority carriers.

Mechanism: When a trivalent dopant substitutes a tetravalent host atom (for example boron in silicon), the dopant has one fewer valence electron than the lattice. An electron from the valence band can occupy the acceptor level, leaving behind a hole in the valence band. The ionized acceptor usually carries a negative charge and is compensated by the hole. The energy required to ionize the acceptor is called the acceptor binding energy or activation energy, and shallow acceptors have small energies, making them ionize at room temperature.

Examples and materials: In silicon, common acceptors are boron, aluminum, and gallium. In GaAs, zinc and carbon can act as acceptors. In wider-bandgap semiconductors, other elements become acceptors with varying ionization energies. The exact ionization energy depends on the crystal and dopant.

Impact and uses: Acceptors are used to create p-type layers in diodes and transistors, form p-n junctions, and enable p-type optoelectronic devices. Their concentration determines the hole density and effective mobility, and high concentrations can lead to compensation if donors are present. Not all implanted impurities become electrically active; some remain as neutral centers or form complexes.