On the mechanism of highly efficient p-type conduction of Mg-doped ultra-wide-bandgap AlN nanostructures

Free hole concentrations up to ∼6 × 1017 cm−3 were measured in Mg-doped AlN nanowires at room-temperature, which is several orders of magnitude larger than that of previously reported AlN epilayers. Detailed studies suggest that such unusually high carrier concentrations stem from the efficient hole hopping conduction in the Mg impurity band, driven by the significantly enhanced Mg-dopant incorporation in nearly defect-free AlN nanostructures. Distinct signatures of hole hopping conduction in the Mg impurity band are observed experimentally, including a relatively small activation energy for electrical conductivity and an increase in hole mobility with increasing temperature.