Free-carrier absorption in nitrides from first principles

We have developed a computationally-tractable first-principles approach (based on density-functional and many-body perturbation theories) to treat the indirect absorption of light by free carriers in semiconductors and insulators and applied it to the technologically important class of group-III nitrides. Indirect absorption by free and impurity-bound carriers, mediated by electron-phonon, charged-defect, and alloy scattering, is an important loss mechanism which may explain the origin of the observed absorption loss in nitride laser devices. The electron-phonon interaction is calculated entirely from first principles, allowing us to validate the commonly used Fröhlich approximation. The formalism is quite general and can be applied to other cases where carrier-induced absorption is a concern, such as in transparent conducting oxides.