Electronic structure and optical spectra of the semimetal ScAs and of the indirect-band-gap semiconductors ScN and GdN

Local (spin) density functional calculations for ScN and GdN are complement ed with estimated quasiparticle corrections and calculations of the optical response to evaluate whether these materials are semimetals as suggested b y some transport measurements or semiconductors as suggested by optical mea surements. The quasiparticle corrections are estimated by assuming that gap corrections are inversely proportional to the dielectric constant and usin g experimentally known results on the quasiparticle d-band shift in ErxSc1- xAs. Results for the optical response functions and band structures are pre sented for ScAs, ScN, and GdN. The conclusion is that whereas ScAs is a sem imetal, ScN and GdN are both narrow gap (0.9 and 0.7-0.85 eV, respectively) indirect gap (T-X) semiconductors, with first direct gap at X at 2.0 and 1 .1-1.2 eV, respectively. Due to the strong exchange interaction of 4f elect rons with the d bands, GdN is predicted to have a magnetic-field-induced re dshift of both the indirect and direct absorption edges of about 0.3 eV.