Reflectivity of the ternary compound Ga(1-x)AlxSb from 2 to 5.5 eV

The reflectivity of the ternary compound Ga (1-x) Al x Sb has been measured on single-crystalline layers from 2 to 5.5 eV for 0<or=x<or=0.73. The variation of the energies E 1 , E 1 + Delta 1 , E' 0 , E' 0 + Delta ' 0 and E 2 with the composition x is reported. A parabolic variation is found for E 1 , E 1 - Delta 1 and Delta 1 , whereas the E 2 transition varies linearly with x. As for the variation of E 1 , the experimental bowing is compared to that calculated by the dielectric two-band method in the virtual crystal approximation, to which a term due to the effects of aperiodicity is added.