Adsorption and desorption processes on beta-Ga2O3 and In2O3 surfaces studied via structural and thermo-/electrical investigations

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The transparent semiconducting oxides beta-Ga2O3 and In2O3 represent a class of wide band-gap semiconductors which attract much attention in research and technology today. While used in the last decades in the form of polycrystalline or amorphous films only, recent results show that bulk single crystals and crystalline epitaxial films with controlled electrical properties have great potential for use as semiconductors with applications in transparent micro-electronics, opto-electronics, short wavelength photonics and in sensor devices. Within this research project we will investigate the structural properties of well-defined surfaces of beta-Ga2O3 and In2O3 bulk single crystals. Reconstructions related to the variation of surface stoichiometry and modifications induced by the adsorption of different molecular gases as well as by the coverage with thin films of gallium and indium on beta-Ga2O3 and In2O3 surfaces, respectively, will be addressed. In particular, we will study the adsorption behaviours of different molecular species such as CO2, CH4, H2, H2O, CH3OH and C2H6O on beta-Ga2O3 and In2O3, which are less well understood. The investigations of the structural and adsorption properties will be performed by the combination of fast atom diffraction (FAD) technique and standard surface analytics like LEED and AES to analyze experimentally the atomic surface structure, i.e. the relaxation, reconstruction, termination, defects, steps and the morphology of the clean and adsorbate-covered surfaces. These structural investigations are relevant to improve growth processes such as MOCVD for epitaxial heterostructures and to the development in the field of molecular electronics on well-defined surface structures. In the framework of surface engineering for sensor applications and the heterogeneous photocatalysis the detailed knowledge of the adsorption and desorption behaviors is essentially. In order to determine the change of surface potential during adsorption and desorption processes, we will measure the electrical conductivity and noise. In particular, on thin single crystalline flakes and epitaxial films we will study the thermo-/electrical properties and their dependence on adsorption and desorption behaviors of different molecular species. These transport investigations are motivated by the opportunities which are given by the well-defined high-quality surfaces of beta-Ga2O3 and In2O3 for epitaxial heterostructures, novel electronic devices as well as a fundamental understanding of the role of surfaces as adsorption layers for conductometric gas sensors.