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

拟议的研究项目的目的是调查外延和性质的硅层与修改晶体结构，所谓的孪生超晶格。利用分子束外延（MBE）技术在Si（111）衬底上生长了孪晶层错，通过控制孪晶层错的掺入，可以制备出不同周期的Si孪晶超晶格。然而，前面的研究表明，超晶格在更大的面积上并不均匀。因此，对超晶格的电学和电子性质的评估是困难的，目前很难得出一般性的结论。不均匀性的主要来源是表面存在的台阶。台阶的存在导致在制备孪晶超晶格期间形成非相干孪晶界，这阻止了规则超晶格结构的形成。 通过在无台阶表面上制备Si层可以克服这个问题。因此，在拟议的项目中，Si（111）衬底将由台面结构化。在这种无台阶的台面上生长出具有改性晶体结构的硅层，并根据结构改性来表征其结构、电学和电子特性。调查集中在不同的Si基半导体结构的电气和电子性能的结构修改的具体影响。 此外，比较研究相对于Si层的无台阶以及阶梯表面上制备的改性晶体结构提供了机会，不仅研究相干孪晶界的具体影响，而且非相干孪晶界，例如，关于载流子传输过程。由于人们对深入了解这些缺陷在许多应用中的特性有很大的兴趣，例如Si基电子和光电子学，因此它也将是拟议项目中的一个主题。

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.