High electron mobility of Al_xGa_(1-x)N evaluated by unfolding the DFT band structure

摘要

We calculate the alloy-disorder-limited electron mobility of Al_xGa_(1-x)N from first principles. Al_xGa_(1-x)N is a technologically important ultra-wide-bandgap alloy with promise in light emitting diodes and high-power transistors. Alloying introduces statistical disorder, which causes electrons to scatter between different crystal-momentum states, leading to a reduction in mobility for intermediate alloy compositions. The corresponding lifetime, which appears as an energy broadening in the band structure, can be evaluated by unfolding the band structure from the supercell basis to the primitive-cell basis. We fit the first-principles band broadening with a model scattering potential 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. We also find the lowest alloy-scattering electron mobility (total electron mobility) across the entire composition range to be 186 cm~2/Vs (136 cm~2/Vs), which is comparable to the highest electron mobility predicted in the competitor system, β-(Al_xGa_(1-x))_2O_3. Our results elucidate the intrinsic limits imposed by alloy disorder on electron transport in Al_xGa_(1-x)N.