Surface states, surface potentials, and segregation at surfaces of tin-dopedIn2O3

Abstract

Surfaces of In 2 O 3 and tin-doped In 2 O 3 (ITO) were investigated using photoelectron spectroscopy. Parts of the measurements were carried out directly after thin film preparation by magnetron sputtering without breaking vacuum. In addition samples were measured during exposure to oxidizing and reducing gases at pressures of up to 100 Pa using synchrotron radiation from the BESSY II storage ring. Reproducible changes of binding energies with temperature and atmosphere are observed, which are attributed to changes of the surface Fermi level position. We present evidence that the Fermi edge emission observed at ITO surfaces is due to metallic surface states rather than to filled conduction band states. The observed variation of the Fermi level position at the ITO surface with experimental conditions is accompanied by a large apparent variation of the core level to valence band maximum binding energy difference as a result of core-hole screening by the free carriers in the surface states. In addition segregation of Sn to the surface is driven by the surface potential gradient. At elevated temperatures the surface Sn concentration reproducibly changes with exposure to different environments and shows a correlation with the Fermi level position.

Fabrication of fully transparent nanowire transistors for transparent and flexible electronics

“…Because oxygen vacancies act as donor states 31,32 , this should increase nanowire conductivity. Although the ITO and IZO microstructures and chemical bonding states are more complex, the basic crystal structures are sufficiently similar to those of In 2 O 3 and ZnO to reasonably expect that the In 2 O 3 and ZnO nanowire work functions will increase similarly upon ozone treatment 30,33 . Thus, the source/drain-nanowire contact should not significantly change with ozone treatment.…”

“…Compared with asfabricated devices, S was reduced from 600 mV dec 21 to 160 mV dec 21 , along with improvement in I on /I off ($1 Â 10 6 ), and a shift in V T from 21.16 V to 20.27 V. The improvement in S is due to change in terms of a reduction in the interfacial trap states and in fixed surface charge states 25 . Ozone treatment not only removes defects and contamination from the nanowire surface, but also changes the work function 29,30 . Ozone is also expected to increase the density of oxygen vacancies near the nanowire surface.…”

Limits for n-type doping in In2O3 and SnO2: A theoretical approach by first-principles calculations using hybrid-functional methodology

“…For example, the formation energy of the double negative oxygen interstitial in In 2 O 3 is ϳ1 eV in the oxidizing limit and for the Fermi energy at the CBM. Since the oxidizing limit is unrealistic at elevated temperatures and the Fermi energy is generally below the CBM for undoped and oxidized In 2 O 3 samples, [40][41][42] we can exclude the occurrence of intrinsic acceptor defects under any experimentally accessible conditions. As can be seen in the left part of Fig.…”

Photoelectronic characterization of heterointerfaces.

“…7, 14, [72][73][74][75][76] Interfacial modifications and/or the presence of adventitious species have been shown to dramatically affect performance of organic electronic devices. 4,5,32 In organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs) charge injection barriers can be present due to energy level offsets, and also due to the presence of undesirable chemical species at the interface.…”

“…37,75,76,[78][79][80][81] Surface roughness, adsorption of adventitious species, and/or a measurement which is still too bulk-sensitive can confound these attempts to evaluate the ITO surface. Additionally, these studies have evaluated the bare ITO surface, without an actual interface with an organic material.…”