Consequences of plasma oxidation and vacuum annealing on the chemical properties and electron accumulation of In2O3 surfaces

Abstract

The influence of oxygen plasma treatments on the surface chemistry and electronic properties of unintentionally doped and Mg-doped In2O3(111) films grown by plasma-assisted molecular beam epitaxy or metal-organic chemical vapor deposition is studied by photoelectron spectroscopy. We evaluate the impact of semiconductor processing technology relevant treatments by an inductively coupled oxygen plasma on the electronic surface properties. In order to determine the underlying reaction processes and chemical changes during film surface - oxygen plasma interaction and to identify reasons for the induced electron depletion, in situ characterization was performed implementing a dielectric barrier discharge oxygen plasma as well as vacuum annealing. The strong depletion of the initial surface electron accumulation layer is identified to be caused by adsorption of reactive oxygen species, which induce an electron transfer from the semiconductor to localized adsorbate states. The chemical modification is found to be restricted to the topmost surface and adsorbate layers. The change in band bending mainly depends on the amount of attached oxygen adatoms and the film bulk electron concentration as confirmed by calculations of the influence of surface state density on the electron concentration and band edge profile using coupled Schroedinger-Poisson calculations. During plasma oxidation, hydrocarbon surface impurities are effectively removed and surface defect states, attributed to oxygen vacancies, vanish. The recurring surface electron accumulation after subsequent vacuum annealing can be consequently explained by surface oxygen vacancies

Towards Understanding the Cross‐Sensitivity of In2O3 Based Ozone Sensors: Effects of O3, O2 and H2O Adsorption at In2O3(111) Surfaces

“…The application of In 2 O 3 as gas sensor is mainly influenced by surface band bending and the distribution of charge carriers. In 2 O 3 exhibits a surface electron accumulation layer (SEAL) after exposure to ambient conditions, which can be depleted by adsorption of reactive oxygen species already shown for the oxygen plasma modified In 2 O 3 surface . This accumulation layer is also observed for other semiconducting oxides like molecular beam epitaxy (MBE) grown single crystalline SnO 2 films or polycrystalline SnO 2 in the absence of oxygen in the surrounding atmosphere .…”

“…The effect of vacuum annealing is extensively discussed in Ref. and we only summarize the most important results in the next paragraph.…”

“…In addition, two different carbon species can be observed at the untreated surface: the large component located at a binding energy of 284.8 eV belongs to hydrocarbon contaminations, the smaller second component at a binding energy of 289.3 eV is caused by carbonate adsorption . These adsorbates were desorbed from the surface by thermal annealing in vacuum at 500 °C, without a significant change of surface band bending and SEAL concentration …”

“…Band structure parameters by Feneberg et al were implemented according to the approach described in detail in Ref. .…”

The Itinerant 2D Electron Gas of the Indium Oxide (111) Surface: Implications for Carbon‐ and Energy‐Conversion Applications

“…the stability of the 2DEG spectral intensity. These observations are accompanied by a shift to lower binding energies of the O 1s (“i” in Figure e), the In 4d (Figure f), and the C 1s core level (Figure g), and a simultaneous decrease in the spectral intensity of the O 1s high binding energy shoulder (“ii” in Figure e,c)—a convolution of adsorbed OH, CO, and O species . Similarly, in this time, the In and O core level intensity increase, while the C 1s intensity decreases (Figure c) (attributed to surface cleaning by the photon beam).…”