A comparison of zinc oxide thin-film transistors on silicon oxide and silicon nitride gate dielectrics

P-type CuI semiconductor films were deposited on the quartz substrates by vacuum evaporation technique, and their morphology, chemical stoichiometry, structure and photoluminescence (PL) characteristics were investigated. The results indicated that, by iodine annealing, the 422 nm emission of the film was improved, whereas the 720 nm emission was reduced, and a (111) preferred orientation in the film was kept unchanged. Through analyzing the time-dependent PL spectrum and the conductivity of the iodine annealed CuI film, the origin of the 422 nm emission was proposed to be related to the copper vacancy. This mechanism was further confirmed by the luminescence characteristics of the film deposited on Cu substrate.

The x-ray excited luminescence spectra of different quality CuI crystals were measured. The prevailing blue luminescence and the unusual red luminescence were found at the same time. The relative intensity of these two luminescence peaks was different because of the change of defect concentration in crystals. By comparing the spectra of CuI crystals before and after annealing in vacuum, air or iodine vapors, the origin of the red luminescence in the as-grown crystals was ascribed to the presence of iodine vacancy, as confirmed by the energy dispersive x-ray analysis.

The polaron introduced by the oxygen vacancy (Vo) dominates many surface adsorption processes and chemical reactions on reduced oxide surfaces. Based on IR spectra and DFT calculations of NO and CO adsorption, we gave two scenarios of polaron-involved molecular adsorption on reduced TiO2(110) surfaces. For NO adsorption, the subsurface polaron electron transfers to a Ti:3d-NO:2p hybrid orbital mainly on NO, leading to the large redshifts of vibration frequencies of NO. For CO adsorption, the polaron only transfers to a Ti:3d state of the surface Ti5c cation underneath CO, and thus only a weak shift of vibration frequency of CO was observed. These scenarios are determined by the energy-level matching between the polaron state and the LUMO of adsorbed molecules, which plays a crucial role in polaron-adsorbate interaction and related catalytic reactions on reduced oxide surfaces.