Investigation on the electronic state of In-doped ZnO nanocrystals by hard X-ray photoemission spectroscopy

ZnO:In nanocrystals (NCs) with various In contents were synthesized by using a mixed source vapor transportation method. The morphological variation and electronic structure of ZnO:In NCs were studied by bulk sensitive hard X-ray photoemission spectroscopy (HX-PES). ZnO:In NCs are classified into ZnO-like hexagonal and In2O3-like cubic groups, based on the crystal structure, and we have estimated the In content for the phase transformation to be as high as 35 atomic% (atm.%). A filled electronic state in the conduction band was observed from the ZnO-like group, which is regarded as a metallic state, due to an increase of extrinsic carrier density.