Electron hole
In physics, chemistry, and electronic engineering, an electron hole (often simply called a hole) is a quasiparticle which is the lack of an electron at a position where one could exist in an atom or atomic lattice. Since in a normal atom or crystal lattice the negative charge of the electrons is balanced by the positive charge of the atomic nuclei, the absence of an electron leaves a net positive charge at the hole's location. Holes in a metal or semiconductor crystal lattice can move through the lattice as electrons can, and act similarly to positively-charged particles. They play an important role in the operation of semiconductor devices such as transistors, diodes and integrated circuits. If an electron is excited into a higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy (and other x-ray techniques), in computational chemistry, and to explain the low electron-electron scattering-rate in crystals (metals, semiconductors). Although they act like elementary particles, holes are not actually particles, but rather quasiparticles; they are different from the positron, which is the antiparticle of the electron. Solids are made of only three kinds of particles: electrons, protons, and neutrons, a quasiparticle is none of these. (See also Dirac sea.) In crystals, electronic band structure calculations lead to an effective mass for the electrons that is typically negative at the top of a band. The negative mass is an unintuitive concept, and in these situations, a more familiar picture is found by considering a positive charge with a positive mass. (Wikipedia).
