The refractive index near the fundamental absorption edge in AlxGa1-xAs ternary compound semiconductors

The real part of the complex refractive index is calculated for photon energies over the region from 1.2 to 1.8 eV for Al_xGa _1-xAs compounds as a function of x. No singularity is predicted. Rather, a change in the functional form of the refractive index, n occurs as the photon energy passes through the bandgap energy, G, leading to a local maximum or, more accurately, a plateau region in n as a function of frequency, which is observed experimentally. The effect of a finite-spin orbit-splitting energy and the effect of higher conduction bands are included. Theoretical and experimental results are compared for Al_xGa _1-xAs over a range of mole fractions from x=0 to x=0.198