Role of hydrogen in hydrogen-induced layer exfoliation of germanium

Abstract

The role of hydrogen in the exfoliation of Ge is studied using cross-sectional transmission electron microscopy, atomic force microscopy, and multiple-internal transmission mode Fourier-transform infrared absorption spectroscopy and compared with the mechanism in silicon. A qualitative model for the physical and chemical action of hydrogen in the exfoliation of these materials is presented, in which H-implantation creates damage states that store hydrogen and create nucleation sites for the formation of micro-cracks. These micro-cracks are chemically stabilized by hydrogen passivation, and upon annealing serve as collection points for molecular hydrogen. Upon further heating, the molecular hydrogen trapped in these cracks exerts pressure on the internal surfaces causing the cracks to extend and coalesce. When this process occurs in the presence of a handle substrate that provides rigidity to the thin film, the coalescence of these cracks leads to cooperative thin film exfoliation. In addition to clarifying the mechanism of H-induced exfoliation of single-crystal thin Ge films, the vibrational study helps to identify the states of hydrogen in heavily damaged Ge. Such information has practical importance for the optimization of H-induced layer transfer as a technological tool for materials integration with these materials systems.