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

透明半导体氧化物β-Ga2O_3和In_2O_3是当今研究和技术关注的一类宽带隙半导体。虽然在过去的几十年里只以多晶或非晶态薄膜的形式使用，但最近的研究结果表明，具有可控电学性质的块状单晶和晶体外延薄膜作为半导体在透明微电子、光电子、短波长光子学和传感器器件中的应用具有巨大的潜力。在这个研究项目中，我们将研究β-Ga2O和In_2O_3大块单晶明确定义的表面的结构特性。对不同分子气体吸附引起的表面化学计量比变化和表面修饰以及在β-Ga2O_3和In_2O_3表面分别覆盖Ga和In薄膜所引起的重构进行了讨论。特别是，我们将研究不同分子物种如CO_2、CH_4、H_2、H_2O、CH_3OH和C_2H_6O在β-Ga_2O_3和In_2O_3上的吸附行为，这些分子物种对β-Ga_2O_3和In_2O_3的吸附较少。结构和吸附性质的研究将结合快速原子衍射(FAD)技术和LEED、AES等标准表面分析技术，对原子表面结构进行实验分析，即原子表面结构的松弛、重构、终止、缺陷、台阶以及清洁和被吸附覆盖的表面的形貌。这些结构研究对于改进外延异质结构的MOCVD等生长过程，以及在定义明确的表面结构上的分子电子学领域的发展具有重要意义。在传感器应用的表面工程和多相光催化的框架下，对吸附和解吸行为的详细了解是必不可少的。为了确定吸附和脱附过程中表面电位的变化，我们将测量电导率和噪声。特别是，在单晶片和外延薄膜上，我们将研究不同分子物种的热/电性质及其对吸附和脱附行为的依赖关系。这些输运研究的动力来自于外延异质结构、新型电子器件以及对表面作为电导型气体传感器的吸附层的基本理解所提供的良好的高质量表面所提供的机会。

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.