Alloy-Limited Electron Mobility of AlGaN Evaluated by Unfolding the DFT Band Structure*

Alloy scattering is the dominant scattering mechanism in the Al_xGa_1-xN alloy system. AlGaN is an ultrawide bandgap semiconductor with promise in deep-ultraviolet LEDs for disinfection and energy-efficient high-power transistors. In this work, we evaluate the intrinsic limit to the low-field electron mobility of AlGaN from first principles. We introduce a method to calculate the quantum scattering lifetime, which appears as an energy broadening in the band structure, by unfolding the band structure from the supercell basis to the primitive-cell basis. We fit a model scattering potential to the first-principles scattering rate data and evaluate the low-field electron mobility using the semiclassical Boltzmann transport equation in the relaxation-time approximation. Our calculated mobility is in agreement with experimental values. The lowest alloy-scattering electron mobility, across the entire composition range of AlGaN, is 186 cm²/Vs, which is comparable to the highest electron mobility predicted in the competitor system (Al_xGa_1-x)₂O₃. Our method can be extended, in the future, to alloys that exhibit preferential atomic ordering and to other types of defect scattering.