Local structure around Zn and Ga in solution‐processed In–Ga–Zn–O and implications for electronic properties

Abstract

International audienceWe study by X-ray absorption spectroscopy the local structure around Zn and Ga in solution-processed In-Ga-Zn-O thin films as a function of thermal annealing. Zn and Ga environments are amorphous up to 450 degrees C. At 200 degrees C and 450 degrees C, the Ga atoms are in a beta-Ga2O3 like structure, mostly tetrahedral gallium oxide phase. Above 300 degrees C, the Zn atoms are in a tetrahedral ZnO phase for atoms inside the nanoclusters. The observed formation of the inorganic structure above 300 degrees C may be correlated to the rise of the mobility for IGZO TFTs. The Zn atoms localized at the nanocluster boundary are undercoordinated with O. Such ZnO cluster boundary could be responsible for electronic defect levels. Such defect levels were put in evidence in the upper half of the band gap. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

In operando x-ray imaging of nanoscale devices: Composition, valence, and internal electrical fields

“…3A , where the absorption edge of metallic Ga is shifted to lower energies compared to the absorption edge of the gallium oxides or GaAs ( 6 , 27 ). The features on the high-energy side of the absorption edge can be used to tentatively identify the coordination number of the absorbing Ga atom by comparison to known coordinations ( 28 ). The first peak at 10,372 eV is most pronounced in GaAs and is attributed to a tetrahedral coordination, whereas the peak at 10,376 eV is more pronounced in the β-Ga 2 O 3 phase and attributed to octahedrally coordinated Ga. Because each Ga atom in the material absorbs x-rays incoherently, a measured XANES spectrum corresponds to the linear combination of the spectra of all configurations present in the given excitation volume.…”

Local Structure Properties of Hydrogenated and Nonhydrogenated Amorphous In–Ga–Zn–O Thin Films Using XAFS and High-Energy XRD

“…However, the observed absorption edges at around 9660 eV for the a-IGZO films are well matched to that of the reference. Indeed, all of these XANES spectra exhibit shoulders at around 9661 eV and peaks at around 9667 eV . The peak maximum located around 9667 eV is attributed to the 1s → 4p transition, which corresponds to Zn 2+ in tetrahedral symmetry .…”

Hot electrons in a nanowire hard X-ray detector

“…There are several works on Ga K-edge XANES measurements that investigate spectral energy shifts in the X-ray absorption edge 32 – 34 . In particular, XANES edges for Ga-based materials with different ligands and coordination states of three, four, and six were reported, and edge energies were found to increase with increasing coordination 33 , 35 .…”