Microwear mechanism of monocrystalline germanium

Germanium (Ge), as a higher mobility material, presents great merits for future semiconductor field-effect transistor devices. Extremely smooth Ge surface is required for high-performance devices, which depends on mechanical surface planarization. However, the defects generated during surface manufacturing usually degrade device performance, which are desired to be minimized to improve the performance and service life of Ge-based products. In this paper, when a light normal load was applied on monocrystalline Ge surface by an atomic force microscope (AFM), the pile-up was generated in the scratched area under line-scan mode by a diamond tip. The formation of the pile-up intensely depends on the contact pressure, and the threshold is about 10.7 GPa, which is close to the microhardness of Ge. Unlike the formation of anodized hillock, the amorphization of Ge was found to be the main contributor to the pile-up induced by the scratch, rather than the oxidation. Based on chemical composition and microstructure detections, it suggests that the pile-up is constructed by thin oxide layer (possibly GeOx (x≤2)) on the surface, thick amorphous layer in the middle and deformed Ge (lattice dislocations excluding amorphization) at the bottom. These findings provide a fundamental understanding of the light-load machining process on monocrystalline Ge surface. •For the first time, friction-induced hillocks were created on Ge(100) surface.•Threshold pressure for the hillock formation is corresponding to Ge hardness.•The amorphization was found to be the main contributor to the hillocks.