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Charge carrier transport properties of Mg-doped Al0.6Ga0.4N grown by molecular beam epitaxy

We have studied the charge carrier transport properties of Mg-doped AlGaN epilayers with Al composition ∼60% grown by plasma-assisted molecular beam epitaxy. At room temperature, free hole concentration up to 8.7 × 1017 cm−3 was measured, and hole mobility values in the range of 10–17 cm2 V−1 s−1 can be reliably achieved. Significantly, a minimum resistivity of 0.7 Ω cm was measured, and its dependence on the Mg dopant incorporation was identified. Detailed temperature-dependent charge carrier transport studies further revealed that the hole concentration exhibited a negligible dependence on temperature near room temperature, but increases drastically for temperatures above 300 °C, suggesting the importance of impurity band conduction at room temperature.