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

提出的研究项目旨在研究具有修饰晶体结构的Si层的外延和性能，即所谓的孪生超晶格。通过分子束外延（MBE）在Si（111）上生长的Si层中控制加入孪晶层错，可以制备出具有不同周期的Si孪晶超晶格。然而，上述研究表明，超晶格在更大的区域内不是均匀的。因此，评价超晶格的电学和电子学性质是困难的，目前很难得出一般的结论。不均匀性的主要来源是地表的台阶。在制备孪晶超晶格的过程中，台阶的存在导致了非相干孪晶边界的形成，从而阻碍了规则超晶格结构的形成。这个问题可以通过在无阶梯表面上制备硅层来克服。因此，在提议的项目中，Si（111）衬底将由台面构成。平台上的剩余台阶随后将通过使用Si MBE的阶梯流生长过程去除。在这种无台阶平台上，将生长出具有改性晶体结构的硅层，并对其结构、电学和电子性能进行表征。研究的重点是结构修饰对不同硅基半导体结构的电气和电子性能的具体影响。此外，对在无阶梯表面和阶梯表面制备的改性晶体结构的Si层进行比较研究，不仅可以研究相干孪晶界的具体影响，还可以研究非相干孪晶界的具体影响，例如，对载流子输运过程的影响。由于在诸如硅基电子和光电子等许多应用中对这些缺陷的性质有更深入的了解，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.