In semiconductors, holes are the absence of an electron in an atom, rather than a physical particle. They can move from atom to atom in semiconducting materials as electrons leave their positions. Holes are formed when electrons in atoms move out of the valence band (the outermost shell of the atom that is completely filled with electrons) into the conduction band (the area in an atom where electrons can escape easily), which happens everywhere in a semiconductor. Holes can be thought of as localized regions of positive charge. Doping with an electron acceptor, an atom which may accept an electron, creates a deficiency of electrons, the same as an excess of holes. Both electrons and holes are vital to the creation of current in semiconductors, and under the influence of some external voltage, both electrons and holes can move through a semiconducting material. Holes play an important role in the operation of semiconductor devices such as transistors, diodes, and integrated circuits.