Grain-Boundary-Aligned Ge Thin Films Formed by Au-Induced Lateral Crystallization with a Multilayer Structure

Abstract

Recent advances in research on polycrystalline Ge thin films have led to the realization of high-speed thin-film transistors that outperform Si. In this study, we investigated metal-induced lateral crystallization (MILC) of Ge, which is a proven grain-boundary control technique for Si thin-film transistors. MILC regions appeared at a low temperature (375 °C) by patterning Au patterns on densified amorphous Ge layers and annealing; however, the growth length was the order of submicrons. We prepared a trilayered amorphous Ge layer in which the deposition temperature and thickness of each layer were modulated to increase the growth velocity and suppress spontaneous nucleation. Machine learning analyses efficiently optimized the parameters of the three layers, which expanded the MILC length by more than 10 times (approximately 10 μm). Evaluation of the crosssectional microstructure revealed that the resulting Ge layer was free of Au contamination and of high quality despite the low synthesis temperature. Furthermore, we found that the type of interlayer influenced the MILC length; the GeO 2 interlayer enabled grain-boundary-aligned Ge crystals of sufficient length, even on plastic films. The technology developed in this study to control Ge grain boundaries at low temperatures will open up the possibility of high-speed thin-film transistors useful for advanced flexible devices.