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Abstract: The electrical and structural properties of HfO2 films on Si1−x Ge x substrates with various Ge concentrations (x =0.1, 0.2, 0.3) were investigated. The behavior of Ge in the interfacial layer (IL) and its effects on the electrical and structural properties after post-annealing were studied in detail. The Ge of the substrate degrades the interfacial properties by interfacial reaction during HfO2 ALD. It also plays an important role in reducing the capacitance equivalent thickness and hysteresis after post-annealing. The improvements in the electrical properties originated from IL thinning due to a drive-out of Ge from the IL and the increase in permittivity of the HfO2 layer due to Hf-Ge-oxide formation. [Copyright &y& Elsevier]