In recent years new fields of research in quantum electronics have been arisen, because of the continuous miniaturization of electronics towards nanoscale. Nanostructures allow to introduce new functionalities which enables the development of novel quantum devices. Furthermore, scientists can engineer the material properties of nanostructures over orders of magnitude, e.g. electrical, optical or magnetic properties. Quantum dots are a very important kind of nanostructures, because of there need for quantum computation, quantum cryptography, logic gates, lasers and solar cells. Now, there are many methods of synthesis available, but it is still a challenge to connect them electrically. One possibility for fabrication of wired quantum dots is a material substitution reaction at a semiconductor nanowire with metallic contacts. Within the scope of this diploma thesis this method of synthesis was studied in order to form nanowires consisting of ultrashort germanium (Ge) segments embedded between monocrystalline aluminium (Al). In order to fabricate these wired germanium quantum dots, germanium nanowires were connected by aluminium contact pads first. Then axial Al-Ge-Al nanowire heterostructures were realized by a thermally activated substitution reaction. During this thermal treatment all structures are heated simultaneously. Because of statistical uncertainties of the substitution reaction the variation in germanium segment lengths is huge. As a result, the yield of nanowire heterostructures with ultrashort germanium segments is very low. The aim of this diploma thesis was to research on alternative methods of heating up the structures separately in order to fabricate quantum dots with target-oriented size. First, Joule heating effects on nanowires due to impressed currents were investigated. In order to monitor the progress of the process the experiments were executed in a scanning electron microscope. The second alternative method under investigation was heating the nanowires with laser light. Here the observation takes place with Raman spectroscopy. The results of Joule heating of Al-Ge-Al nanowire heterostructures shows that the reduction of the segment length is limited at long segments and could lead to a complete substitution at short segments. The method of heating Al-Ge-Al nanowire heterostructures with laser light seams to be an appropriate method of synthesis for wired germanium quantum dots.