Fabrication of locally defined Ge:Mn-Hybridstructures with self organized processes during pulsed laser annealing

• Applicant: Dr. Danilo Bürger
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Experimental Condensed Matter Physics ; Synthesis and Properties of Functional Materials ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2013 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 233957617

The research proposal is related to the fabrication and characterization of self-organized Ge:Mn hybrid structures. Those hybrid structures are formed due to the Mullins-Sekerka instability during melting of the surface of a germanium-manganese (Ge-Mn)-alloy by pulsed laser irradiation. The occurrence of an Mullins-Sekerka instability is rather unlikely during melting with short pulses of excimer lasers. We used a solid-state laser with pulse lengths between 300 ns and 1200 ns and fabricated a percolating, ferromagnetic, manganese-rich, amorphous Ge:Mn nanonet with nanowire diameters below 10 nm embedded in manganese-poor, crystalline germanium.Above a critical Mn concentration, the manganese is not completely incorporated into the crystalline germanium during recrystallization of the molten Ge-Mn alloy and accumulates in the liquid phase of the Ge-Mn alloy. In the Mn-rich area the melting temperature of the Ge-Mn alloy locally decreases. If the local temperature in the liquid phase of the Ge-Mn alloy due to the specific laser pulse length lies below its local melting temperature, a constitutional supercooled melt is fabricated. The recrystallization of such a supercooled liquid is highly instable which is the main requirement to fabricate Ge:Mn hybrid structures. In the next step ordered Ge:Mn hybrid structures will be created by forming a periodic Mn distribution before pulsed laser treatment and by selective chemical etching of manganese-rich regions of the Ge-Mn alloy after pulsed laser treatment. The structured germanium surface reveals the same structure size as the etched manganese-rich regions of the Ge-Mn alloy. Such structure sizes < 10 nm cannot be fabricated by conventional optical lithography and are important for the nanoimprint lithography.Moreover, we have shown that the magnetization and anomalous Hall effect of percolating Ge:Mn nanonets are strongly correlated. This specific property has only been known from the well known diluted ferromagnetic semiconductor GaAs:Mn. Therefore, the fabrication of percolating ferromagnetic nanonets represents a new approach in spintronics for the combination of magnetic and semiconducting properties for information processing. The presented proposal is related to research work on nanoimprint-lithography and on transport of spinpolarized charge carriers in magnetic nanostructures.

• DFG Programme: Research Grants