A CMOS compatible Ge avalanche photodiode is fabricated on Si by using a selective chemical-vapor deposition (CVD) epitaxial growth technique. At a temperature of 700°C, single crystal islands of As-doped Ge are grown in windows to the Si with sizes up to hundreds of μm2, to a layer thickness of approximately 1 μm, This is followed by a pure Ga and then a pure B (PureGaB) deposition for the creation of an ultrashallow p+-region that can be metallized by Al. The resulting p+n diodes have exceptionally good I-V characteristics with ideality factors of ~ 1.1 and reliably low saturation currents. The measurements show high sensitivity of the photodiodes to IR wavelengths above 1 μm in avalanche and Geiger modes.