We review recent attempts to understand the experimentally observed doping limitations in wide gap II-VI compounds. These attempts can be divided into three groups: ab initio density functional calculations, thermodynamical considerations based on the mass action law, and a pragmatic model that assumes a pinning of the Fermi level with respect to the vacuum level. These approaches give many important hints on the nature of compensation, showing that limited solubilities, the formation of complexes involving intrinsic and extrinsic defects, and Fermi level pinning are important factors. The latter is also important for the formation of Ohmic contacts to p-ZnSe, where diffusing nitrogen leads to an enhanced resistivity of the p-ZnSe underneath the contact. direct c 1999 Elsevier Science B.V. All rights reserved.
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