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Statistical properties of the Magnesium acceptor in GaN

The selection of the acceptor dopants for the nitride semiconductors is rather reduced, and only Magnesium is known to produce reliable p-type conductivity. The energy level of Mg is deep, therefore, large concentrations of Mg-acceptors are needed, as a rule, well over 10^19cm^-3. Typical free carrier concentrations are in the low 10^17cm^-3 range, and only in few cases concentrations slightly above 10^18cm^-3 have been reported. In spite of numerous experimental results, the energy level of Magnesium is not known precisely. Experimental values are spanned from below 100meV to above 200meV. Reported degrees of compensation differ, depending on the growth condition and post-growth treatment. Interpretations of the Hall constant measurements versus temperature in the literature are sometimes vague and, in addition, frequently perplexed by the appearance of two conductive layers and/or impurity band conduction at lower temperatures. Here, we analyze experimentally and theoretically the dependence of the free carrier concentration on temperature [p(T)]. The ambiguities and proper interpretation of experimental results are examined in detail. Recently determined effective hole mass is used in the analysis [B.Santic, Semic.Sci.Techn.18(2003)219]. The value for the ionization energy of Mg acceptor is resolved. The review of literature data is presented as well. The role of the degeneracy factor ('g'-value) for Mg-level in the statistics is examined and shown to play a significant role, enabling an indirect link to the microstructure of Mg dopant.

Semiconductors; GaN; Mg; doping

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