Optical consequences of long-range order in wurtziteAlxGa1−xNalloys

The effect of 1:1 long range order on optical properties of ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ alloys is investigated by means of first-principles calculations combined with large-scale atomistic empirical-pseudopotential simulations. We propose an intra-band mechanism of ordering-induced band gap reduction for different optical polarization. The scaling of band gap reductions with order parameter is analyzed. Our simulations of inhomogeneous ordering suggest that coexistence of ordered and random domains may explain the large magnitude of the observed redshifts upon ordering.