Built‐in Nanostructures in Transparent Oxides for Novel Photonic and Electronic Functions Materials

We review distinct photonic/electronic properties originating from built‐in nanostructures in transparent oxide‐based materials, emphasizing potential of nanostructures hidden in crystal structure. Materials focused on are oxychalcogenides LaCuOCh (Ch = chalcogen ion) and homologous oxides InGaO 3 (ZnO) m (m = integer) having naturally formed multi‐quantum well structures and 12CaO· 7Al 2 O 3 (C12A7) with a unique nanoporous structure. Novel functions and devices arising from the built‐in nanostructure are: (1) modulation doping of positive holes and room‐temperature stable exciton in LaCuOCh, (2) high‐performance transparent field‐effect transistor fabricated in InGaO 3 (ZnO) 5 epitaxial thin films, and (3) conversion of insulator to persistent electronic conductor by carrier doping in 12CaO·7Al 2 O 3 (C12A7).