The electrical and physical properties of atomic-layer-deposited (ALD) HfO2 on strained and relaxed Si1-xGex after postdeposition annealing (PDA) were studied. The Ge atoms which diffused into HfO2 during ALD migrated toward the substrate during PDA. The Ge recession, densification of the film, and suppression of the Si diffusion into the film caused by the thicker interfacial layer at a higher Ge concentration play key roles in reducing the capacitance equivalent thickness (CET) after PDA. The suppression of the Si diffusion into HfO2 on relaxed Si1-xGex results in a further reduction of the CET. (c) 2007 The Electrochemical Society.