Investigations of the electronic and electrical properties of Si twinning-superlattices in Si-based semiconductor structures on step-free Si(111)-mesas

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The proposed research project is aimed at the investigation of epitaxy and properties of Si layers with modified crystal structure, so-called twinning superlattices. Si twinning superlattices with different periodicity will be prepared by the controlled incorporation of twinning stacking faults in Si layers grown by molecular beam epitaxy (MBE) on Si(111). The forgoing Investigations showed, however, that the superlattices are not homogeneous across larger areas. The evaluation of electrical and electronic properties of the superlattices is therefore difficult, what at present hardly allows general conclusions. The main source of inhomogeneity are steps present at the surface. The presence of steps results in the formation of incoherent twin boundaries during the preparation of the twinning superlattices, what prevents the formation of a regular superlattice structure. The problem could be overcome by preparation of the Si layers on step-free surfaces. In the proposed project therefore Si(111) substrates will be structured by mesas. The remaining steps on the mesas will be removed subsequently via step-flow growth process using Si MBE.On such step-free mesas Si layers with modified crystal structure will be grown and characterized regarding their structural, electrical and electronic properties in dependence on the structural modification. The investigations focus on the specific impact of structural modification on the electrical and electronic properties of different Si based semiconductor structures. Furthermore, comparative studies with respect to Si layers with modified crystal structure prepared on step-free as well as stepped surfaces give the opportunity to study not only the specific impact of coherent twin boundaries but also of incoherent twin boundaries, for example, with regard to the carrier transport process. Since there is a large interest in a deeper understanding of properties of these defects for a lot of applications, such as Si-based electronic and optoelectronics, it will be also a subject within the proposed project.