Low Energy Ion-Induced Crystallization of Ge in c-Al/a-Ge Bilayer Thin Films at Low Temperatures of 125 C

The fabrication of polycrystalline Ge films at relatively low temperatures is of great importance for their applications in advanced microelectronic and solar cell devices. In this paper, we present the crystallization of Ge in a c-Al/a-Ge bilayer system at a temperature of 125 degrees C (lowest ever) using low energy ion beam irradiation followed by post-thermal annealing. The c-Al/a-Ge bilayer thin films are irradiated with 500 keV Kr+ and Xe+ ions at different fluences and then postannealed at a fixed temperature of 200 degrees C. The postannealing of the samples at a fixed temperature of 200 degrees C leads to the formation of polycrystalline Ge, and the crystallinity is observed to increase with increasing ion fluence. The crystallinity is found to be better in the samples irradiated by Xe+ ions as compared to the Kr+ ions. It is also observed that the thermal annealing of ion-irradiated samples yields better crystallinity than that of the samples that are annealed without irradiation. A temperature-dependent Raman measurement on samples irradiated with a fluence of 1 x 10(16) ions cm(-2) reveals the crystallization of Ge at 125 degrees C. The concepts of layer exchange and irradiation-enhanced kinetics are invoked to explain the crystallization of Ge via different characterization techniques and by using the transport of ions in matter computer simulation code. The presented paper demonstrates the development of polycrystalline Ge at a relatively low temperature using a unique technique of ion irradiation, which may be realized for high performance advanced devices in the future.