Optical band gap of the filled tetrahedral semiconductor LiZnP

We report on the optical band gap of the filled tetrahedral (Nowotny-Juza) compound LiZnP [viewed as a zinc-blend-like (ZnP${)}^{\mathrm{-}}$ lattice partially filled with He-like ${\mathrm{Li}}^{+}$ interstitials]. The band-gap nature of LiZnP predicted theoretically by an ‘‘interstitial insertion rule’’ is confirmed to be direct with a forbidden gap of 2.04±0.01 eV at room temperature. The typical resistivity, Hall mobility, and electron concentration at room temperature are of the order of 10 Ω cm, 25 ${\mathrm{cm}}^2$/V sec, and ${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$, respectively. The empirical trend of band gaps between the filled tetrahedral and zinc-blende structures is discussed.