As); tin, silicon, germanium (substituting Ga) p-type: beryllium, zinc, chromium (substituting Ga); silicon, germanium, carbon (substituting As) Gallium phosphide n-type: tellurium, selenium, sulfur (substituting phosphorus) p-type: zinc, magnesium (substituting Ga); tin (substituting P) isoelectric: nitrogen (substituting P) is added to enable luminescence in older green LEDs (GaP has indirect band gap) Gallium nitride, Indium gallium nitride, Aluminium gallium nitride n-type: silicon (substituting Ga), germanium (substituting Ga, better lattice match), carbon (substituting Ga, naturally embedding into MOVPE-grown layers in low concentration) p-type: magnesium (substituting Ga) - challenging due to relatively high ionisation energy above the valence band edge, strong diffusion of interstitial Mg, hydrogen complexes passivating of Mg acceptors and by Mg self-compensation at higher concentrations) Cadmium telluride n-type: indium, aluminium (substituting Cd); chlorine (substituting Te) p-type: phosphorus (substituting Te); lithium, sodium (substituting Cd) Cadmium sulfide n-type: gallium (substituting Cd); iodine, fluorine (substituting S) p-type: lithium, sodium (substituting Cd) Compensation In most cases many types of impurities will be present in the resultant doped semiconductor. If an equal number of donors and acceptors are present in the semiconductor, the extra core electrons provided by the former will be used to satisfy the broken bonds due to the latter, so that doping produces no free carriers of either type. This phenomenon is known as compensation, and occurs at the p-n junction in the vast majority of semiconductor devices. Partial compensation, where donors outnumber acceptors or vice versa, allows device makers to repeatedly reverse (invert) the type of a certain layer under the surface of a bulk semiconductor by diffusing or implanting successively higher doses of dopants, so-called counterdoping. Most modern semiconductor devices are made by successive selective counterdoping steps to create the necessary P and N type areas under the surface of bulk silicon. This is an alternative to successively growing such layers by epitaxy. Although compensation can be used to increase or decrease the number of donors or acceptors, the electron and hole mobility is always decreased by compensation because mobility is affected by the sum of the donor and acceptor ions. Doping in conductive polymers Conductive polymers can be doped by adding chemical reactants to oxidize, or sometimes reduce, the system so that electrons are pushed into the conducting orbitals within the already potentially conducting system. There are two primary methods of doping a conductive polymer, both of which use an oxidation-reduction (i.e., redox) process. Chemical doping involves exposing a