Silicon germanium (SiGe) is a multi-functional material considered for quantum computing, neuromorphic devices and CMOS transistors. However, implementation of SiGe in nano-scale electronic devices necessitates suppression of surface states dominating on electronic properties. The absence of a stable and passive surface oxide for SiGe results formation of charge traps at the SiGe -oxide interface induced by GeO x . In an ideal ALD process in which oxide is grown layer-by-layer, the GeO x formation should be prevented with selective surface oxidation (i.e. formation of an SiO x interface) by controlling oxidant dose in first few ALD cycles of the oxide deposition on SiGe. However, in a real ALD process, the interface evolves during entire ALD oxide deposition due to diffusion of reactant species through the gate oxide. In this work, this diffusion process in non-ideal ALD is investigated and exploited: the diffusion through the oxide during ALD is utilized to passivate the interfacial defects by employing ozone as a secondary oxidant. Periodic ozone exposure during gate oxide ALD on SiGe is shown to reduce the integrated trap density (D it ) across the band gap by nearly an order of magnitude in Al 2 O 3 (< 6×10 10 cm -2 ) and in HfO 2 (< 3.9×10 11 cm -2 ) by forming a SiO x rich interface on SiGe. Depletion of Ge from the interfacial layer (IL) by enhancement of volatile GeO x formation and consequent desorption from the SiGe with ozone insertion during ALD growth process is confirmed by electron energy loss spectroscopy (STEM-EELS) and hypothesized to be the mechanism for reduction of the interfacial defects. In this work, the nanoscale mechanism for defect suppression at SiGe oxide interface is demonstrated which is engineering of diffusion species in ALD process due to facile diffusion of reactant species in non-ideal ALD.