Intrinsic excitonic photoluminescence and band-gap engineering of wide-gap p-type oxychalcogenide epitaxial films of LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) semiconductor alloys

The optical spectroscopic properties of layered oxychalcogenide semiconductors LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) on epitaxial films were thoroughly investigated near the fundamental energy band edges. Free exciton emissions were observed for all the films between 300 and ~30 K. In addition, a sharp emission line, which was attributed to bound excitons, appeared below ~80 K. The free exciton energy showed a nonmonotonic relationship with lattice constant and was dependent on lanthanide and chalcogen ion substitutions. These results imply that the exciton was confined to the (Cu2Ch2)2– layer. Anionic and cationic substitutions tune the emission energy at 300 K from 3.21 to 2.89 eV and provide a way to engineer the electronic structure in light-emitting devices

Intrinsic excitonic photoluminescence and band-gap engineering of wide-gap p-type oxychalcogenide epitaxial films of LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) semiconductor alloys

The optical spectroscopic properties of layered oxychalcogenide semiconductors LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) on epitaxial films were thoroughly investigated near the fundamental energy band edges. Free exciton emissions were observed for all the films between 300 and ~30 K. In addition, a sharp emission line, which was attributed to bound excitons, appeared below ~80 K. The free exciton energy showed a nonmonotonic relationship with lattice constant and was dependent on lanthanide and chalcogen ion substitutions. These results imply that the exciton was confined to the (Cu2Ch2)2– layer. Anionic and cationic substitutions tune the emission energy at 300 K from 3.21 to 2.89 eV and provide a way to engineer the electronic structure in light-emitting devices

Preparation and crystal structure analysis of CeCuOS

A single phase of CeCuOS was prepared by sulfurization of starting materials, CeO2+Cu2S, and subsequent post-annealing in evacuated silica tubes. The crystal structure of the CeCuOS single phase was examined by the Rietveld analysis. The shrinkage of the unit cell volume for CeCuOS was obviously observed in the series of LnCuOS (Ln=La∼Nd) oxysulfides. The examination of interatomic distances revealed that Ce-S distances in CeCuOS are shorter than those predicted from the lanthanide contraction and this short Ce-S bond length is responsible for the unit-cell-volume shrinkage of CeCuOS. The origin of the shrinkage is discussed in the viewpoints of the Ce valence and interatomic distances along with the results of magnetic measurements

Optoelectronic properties and electronic structure of YCuOSe

YCuOSe was prepared by solid-state reaction, and its wide gap semiconducting properties were examined. The single phase of YCuOSe was obtained in a limited temperature range around 750 °C and decomposed into Y2O2Se and Cu2Se at higher temperatures. The obtained YCuOSe sample showed a p-type semiconducting behavior with the electrical conductivity of 1.4×10−1 S cm−1 at room temperature. The band gap of YCuOSe was estimated to be 2.58 eV, which is much smaller than that of LaCuOSe (2.82 eV). The electronic structure of YCuOSe was investigated by ultraviolet photoemission spectroscopy and energy band calculations to understand the differences in the electronic structures between LnCuOSe (Ln=La,Y). It was found that the Cu–Cu distance rather than the Cu–Se distance influences the electronic structures, and the smaller band gap of YCuOSe is attributed to the downshift of the Cu 4s energy level due to the smaller Cu–Cu distance and the consequent larger Cu–Cu interaction in YCuOSe

Intrinsic excitonic photoluminescence and band-gap engineering of wide-gap p-type oxychalcogenide epitaxial films of LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) semiconductor alloys

The optical spectroscopic properties of layered oxychalcogenide semiconductors LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) on epitaxial films were thoroughly investigated near the fundamental energy band edges. Free exciton emissions were observed for all the films between 300 and ~30 K. In addition, a sharp emission line, which was attributed to bound excitons, appeared below ~80 K. The free exciton energy showed a nonmonotonic relationship with lattice constant and was dependent on lanthanide and chalcogen ion substitutions. These results imply that the exciton was confined to the (Cu2Ch2)2– layer. Anionic and cationic substitutions tune the emission energy at 300 K from 3.21 to 2.89 eV and provide a way to engineer the electronic structure in light-emitting devices

Optoelectronic properties and electronic structure of YCuOSe

YCuOSe was prepared by solid-state reaction, and its wide gap semiconducting properties were examined. The single phase of YCuOSe was obtained in a limited temperature range around 750 °C and decomposed into Y2O2Se and Cu2Se at higher temperatures. The obtained YCuOSe sample showed a p-type semiconducting behavior with the electrical conductivity of 1.4×10−1 S cm−1 at room temperature. The band gap of YCuOSe was estimated to be 2.58 eV, which is much smaller than that of LaCuOSe (2.82 eV). The electronic structure of YCuOSe was investigated by ultraviolet photoemission spectroscopy and energy band calculations to understand the differences in the electronic structures between LnCuOSe (Ln=La,Y). It was found that the Cu–Cu distance rather than the Cu–Se distance influences the electronic structures, and the smaller band gap of YCuOSe is attributed to the downshift of the Cu 4s energy level due to the smaller Cu–Cu distance and the consequent larger Cu–Cu interaction in YCuOSe