Electrical and photonic functions originating from low-dimensional structures in wide-gap semiconductors LnCuOCh (Ln = lanthanide, Ch = chalcogen): A review

Abstract

This article reviews novel electrical and optical properties found for epitaxial thin films of wide-gap semiconductors, LnCuOCh (Ln = lanthanide, Ch = chalcogen). This material series has a two-dimensional crystal structure composed of alternately stacked (Ln2O2)2+ and (Cu2Ch2)2- layers. Distinctive properties such as high hole mobility, degenerate p-type conduction, room temperature exciton, and large optical nonlinearity were found and these are attributed to two-dimensional electronic structure arising from the layered structure, i.e., a narrow-gaped and hole-conductive (Cu2Ch2)2- layer is sandwiched by wide-gaped insulating (Lu2O2) 2+ layers. In particular, the wide-gap p-type metallic conduction was the first demonstration among any class of wide-gap materials including GaN: Mg. Realization of epitaxial thin films for these materials by reactive solid-phase epitaxy led to these discoveries which make LnCuOCh promising materials for optoelectronic devices utilizing the high p-type conductivity and/or the room temperature exciton.