Molekularstrahlepitaxie von Zn1-XMnXSe-basierten semimagnetischen Halbleiter-Heterostrukturen sowie Untersuchungen zu ihren strukturellen, elektrischen und optischen Eigenschaften (English shop)

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This work addresses the fabrication of Zn1−xMnxSe-based semimagnetic II-VI semiconductor heterostructures by means of molecular beam epitaxy and investigations of their structural, electrical and optical properties. A first objective of the work was the controlled fabrication of Zn1−xMnxSe bulk layers and their characterization. The use of an excess supply of selenium proved favourable for the growth quality. While experimenting with RHEED oscillations to determine the growth rate of Zn1−xMnxSe, it was noticed that thin MnSe films also exhibited very pronounced RHEED oscillations at a low Mn flux and hence a high excess of Se. Since the MnSe film thickness could be determined very precisely in this way, and the layer systems consisting of ZnSe and MnSe were characterized by high-quality two-dimensional growth, the investigation of ZnSe/MnSe superlattices was worthwhile. Initially, owing to the exact control of the ratio of the numbers of ZnSe and MnSe monolayers, they were used to verify the composition determinations of Zn1−xMnxSe samples by means of EDX, PIXE and Rutherford backscattering, since measurement methods that average over a large number of lattice constants in the sample do not distinguish between a superlattice and an alloy semiconductor with the same proportions of the components. A further method of composition determination is X-ray diffractometry, provided that the composition dependence of the lattice constant and of the elastic constants is known. In order to determine this relationship as precisely as possible, Zn1−xMnxSe samples were fabricated over a wide composition range within the framework of this work and investigated crystallographically. It turned out that epitaxial growth in the zinc blende structure is still possible even for very high manganese contents, and likewise for MnSe, although in both cases the wurtzite structure is the thermodynamically more stable form. The defect density increases strongly with the manganese content, while it remains very low for x < 0.05, the range of interest for spin aligners.