Natural nanostructures in ionic semiconductors

Nanostructures naturally formed in oxide semiconductor crystals are discussed in relation to their electronic structure and properties. Three different crystals are studied: (i) layered oxychalcogenides LnCuOCh (Ln=lanthanide, Ch=chalcogen), (ii) homologous series layered oxides RMO3(ZnO)m (R=In, Lu etc., M=In, Ga etc., <f>m</f>=integer), and (iii) nanoporous crystal 12CaO7 <f>·</f> Al2O3 (C12A7). Coexistence of moderately large mobility, intense photoluminescence arising from room-temperature exciton and high-density hole is explained by a natural modulation doping structure in LnCuOCh. C12A7 exhibits different properties by replacing free O2- ions anions clathrated in its subnanometer-sized cages with O-, H-, and electron. The electronic structures of the clathrated anions were investigated by ab initio calculations and discussed in terms of possible quantum structures and applications. [Copyright &y& Elsevier]