Electronic structure of filled tetrahedral semiconductors

We discuss the susceptibility of zinc-blende semiconductors to band-structure modification by insertion of small atoms at their tetrahedral interstitial sites. GaP is found to become an indirect-gap semiconductor with two He atoms present at its interstitial sites; Si does not. Analysis of the factors controlling these filling-induced electronic modifications allows us to predict that LiZnP [viewed as a zinc-blende-like (ZnP${)}^{\mathrm{-}}$ lattice partially filled with He-like ${\mathrm{Li}}^{+}$ interstitials], as well as other members of the Nowotny-Juza compounds $A^{\mathrm{I}{B}^{\mathrm{II}{O}^{\mathrm{V}}}}$, are likely to be a novel group of direct-gap semiconductors.