Mg-doped superlattices consisting of uniformly doped AlxGa1−xN and GaN layers are analyzed by Hall-effect measurements. Acceptor activation energies of 70 meV and 58 meV are obtained for superlattice structures with an Al mole fraction ofx = 0.10 and 0.20 in the barrier layers, respectively. These energies are significantly lower than the activation energy measured for Mg-doped GaN thin films. At room temperature, the doped superlattices have free hole concentrations of 2 × 1018 cm−3 and 4 × 1018 cm−3 forx = 0.10 and 0.20, respectively. The increase in hole concentration with Al content of the superlattice is consistent with theory. The room temperature conductivity measured for the superlattice structures are 0.27 S/cm and 0.64 S/cm for an Al mole fraction ofx = 0.10 and 0.20, respectively.
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We use εr = 9.0 and εr = 8.5 for the relative dielectric constant for GaN and AlN, respectively. These values are compiled in Reference 1.
The experimental effective hole mass in AlxGa1.xN is unknown at this time. Although, Katsuragawa et al. in Reference 7 reported no significant change in the activation energy of Mg in AlxGa1.xN indicating no significant change in the hole mass. See, for instance, Gil, Group III Nitride Semiconductor Compounds (Clarendon Press, Oxford, 1998)
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Goepfert, I.D., Schubert, E.F., Osinsky, A. et al. Efficient Acceptor Activation in AlxGa1−xN/GaN Doped Superlattices. MRS Online Proceedings Library 595, 385 (1999). https://doi.org/10.1557/PROC-595-F99W3.85