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In this letter, we present a fundamental study on the scalability and electrical properties of germanium oxynitride dielectrics for metal-oxide-semiconductor device applications. The nitrogen depth profile within the oxynitride dielectric layers was first monitored using angle-resolved x-ray photoemission spectroscopy and the dielectric permittivity variation was therefore identified. After thinning down the lower permittivity portion of these dielectrics, we successfully scaled down the capacitance-based equivalent SiO2 thickness, in Ge MOS capacitors, to 1.9 nm without suffering from gate leakage. We have also investigated the effects of thermal annealing on various capacitor electrical properties. For instance, we measured a flat-band voltage shift of as much as -0.8 V from the ideal value on as-deposited capacitors and the recovery of the theoretical value, with acceptably small amount of oxide fixed charge, after subsequent thermal annealing. Lastly, we have benchmarked the performance of these oxynitride insulators with the advanced high-κ dielectrics on Ge and discussed the impacts on future scaling.