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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

Preparation of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (In 2 O 3 ), is often challenged by the presence of a distinct surface electron accumulation layer. We investigated the material properties and electrical transport characteristics of platinum contact/indium oxide heterojunctions to define routines for the preparation of high-performance Schottky diodes on n-type oxide semiconductors. Combining the evaluation of different Pt deposition methods, such as electron-beam evaporation and (reactive) sputtering in an (O and) Ar atmosphere, with oxygen plasma interface treatments, we identify key parameters to obtain Schottky-type contacts with high electronic barrier height and high rectification ratio. Different photoelectron spectroscopy approaches are compared to characterize the chemical properties of the contact layers and the interface region toward In 2 O 3 , to analyze charge transfer and plasma oxidation processes as well as to evaluate the precision and limits of different methodologies to determine heterointerface energy barriers. An oxygen-plasma-induced passivation of the semiconductor surface, which induces electron depletion and generates an intrinsic interface energy barrier, is found to be not sufficient to generate rectifying platinum contacts. The dissolution of the functional interface oxide layer within the Pt film results in an energy barrier of ∼0.5 eV, which is too low for an In 2 O 3 electron concentration of ∼10 18 cm −3 . A reactive sputter process in an Ar and O atmosphere is required to fabricate rectifying contacts that are composed of platinum oxide (PtO x ). Combining oxygen plasma interface oxidation of the semiconductor surface with reactive sputtering of PtO x layers results in the generation of a high Schottky barrier of ∼0.9 eV and a rectification ratio of up to 10 6 . An additional oxygen plasma treatment after contact deposition further reduced the reverse leakage current, likely by eliminating a surface conduction path between the coplanar Ohmic and Schottky contacts. We conclude that processes that allow us to increase the oxygen content in the interface and contact region are essential for fabrication of device-quality-rectifying contacts on various oxide semiconductors.

The interaction of ozone, oxygen, and water molecules with the (111) surface of indium oxide grown by plasma‐assisted molecular beam epitaxy is investigated. In order to characterize the adsorption and charge transfer mechanisms taking place at ozone‐sensitive In2O3 films and to determine the effect of humidity, we study the chemical and electronic surface properties using photoelectron spectroscopy. Clean surfaces are prepared by vacuum annealing and subsequently exposed to O3, O2, or H2O in serial adsorption sequences. After ozone and oxygen interaction, the same adsorbate species are detected and both molecules reduce the surface electron density, resulting in a decrease of film conductance. However, the quantitative changes of adsorbate coverage, band bending, surface electron concentration, and work function indicate a much higher reactivity of the surface with ozone. In contrast, if the surface is exposed to water, the resulting adsorbates have a different spectroscopic signature and do not significantly alter surface band bending and electron concentration. The effects of ozone/oxygen interaction are weakened if the surface was pre‐exposed to water. These results indicate that water adsorbates occupy surface sites that are consequently not available for ozone interaction and that humidity influences the device sensitivity but not its selectivity toward oxidizing gases.

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