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

快速重离子束是研究高局部电子能量沉积对固体结构和性能变化影响的有效工具。在大多数绝缘体和金属中，由于快速重离子辐照引起的高电子激发会导致在离子轨迹周围形成无定形轨道。这种效应通常用热尖峰模型的框架来解释，假设材料熔化，然后快速冷却和再凝固。在技术相关的半导体领域，情况就不那么明朗了。特别是到目前为止，缺乏足够可靠的实验数据，阻碍了对过程的最终理解，也阻碍了一个没有矛盾的理论描述。因此，拟议研究的主要目标是有助于进一步澄清物理过程，特别是证明在快速重离子照射下半导体中可能存在熔化相。为此，我们将研究不同掺杂类型和浓度的快速重离子辐照半导体（Si, GaAs, InP）的损伤演化和退火过程与电子能量沉积、离子质量和离子速度以及不同辐照温度下撞击离子的电荷状态的关系。实验将伴随着热尖峰模型框架内的模型模拟，结合实验数据，得出在高电子激发下发生的相变的结论。除了基础方面，在实现深埋改性层、纳米结构的合成以及在超高能量粒子加速器和空间应用中快速离子诱导器件失效方面的研究具有明显的实际意义。

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.