In this study, we investigate directly bonded germanium-silicon interfaces to facilitate the development of high quality germanium silicon integration for Avalanche photodiode application. Angle resolved x-ray photoelectron spectroscopy data is presented which provides the chemical composition of the germanium surfaces as a function of the surface passivation. The hetero-structure is characterized by measuring forward and reverse current and comparing the measured results to TCAD simulation. The physical structure of hetero-junction is supported by high resolution transmission electron microscopy. © 2011 Materials Research Society.