Microscopic origin of the phenomenological equilibrium "doping limit rule'' in n-type III-V semiconductors

The highest equilibrium free-carrier doping concentration possible in a giv en material is limited by the "pinning energy" which shows a remarkable uni versal alignment in each class of semiconductors. Our first-principles tota l energy calculations reveal that equilibrium n-type doping is ultimately l imited by the spontaneous formation of close-shell acceptor defects: the (3 -)-charged cation vacancy in AlN, GaN, InP, and GaAs and the (1-)-charged D X center in AlAs, AlP, and GaP. This explains the alignment of the pinning energies and predicts the maximum equilibrium doping levels in different ma terials.