Non-equilibrium phase transitions in crystalline semiconductors under swift heavy ion irradiation

• Applicant: Professor Dr. Werner Wesch
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2004 to 2007
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5438441

Swift heavy ion beams are a useful tool for a separate study of the effect of high local electronic energy deposition on structural and property modifications in solids. In most insulators and metals the high electronic excitation due to swift heavy ion irradiation is known to result in amorphous track formation around the ion trajectories. This effect is commonly explained in the framework of a thermal spike model assuming melting of the material followed by fast cooling and re-solidification. In the technologically relevant semiconductors the situation is much less clear. Especially the lack of sufficiently reliable experimental data up to now prevents the final understanding of the processes as well as a theoretical description free of contradictions. It is therefore the main goal of the proposed research to contribute to a further clarification of the physical processes, particularly to proof the possible existence of a melt phase in semiconductors under swift heavy ion irradiation. For this purpose, the damage evolution and annealing in swift heavy ion irradiated semiconductors (Si, GaAs, InP) of different doping type and concentration will be studied as a function of the electronic energy deposition, the ion mass and ion velocity, and the charge state of the impinging ions at different irradiation temperatures. The experiments will be accompanied by model simulations in the framework of the thermal spike model enabling, in connection with the experimental data, conclusions about the phase transitions occurring under high electronic excitation. Apart from the basic aspect, the practical relevance of the research with regard to the realisation of deeply buried modified layers, the synthesis of nanostructures and swift ion induced device failure in super-high energy particle accelerators and space applications is obvious.

• DFG Programme: Research Grants