We report a Ge growth technique on Si using thin SiGe buffer layers and also discuss photodiodes fabricated on the Ge for Si CMOS monolithic optical receiver applications. The effectiveness of thin SiGe buffer layers in terminating threading dislocations and reducing photodiode dark current for Ge epitaxially grown on Si (001) has been investigated for Ge photodiodes. The dark current of Ge on Si photodiodes can be reduced by over an order of magnitude by incorporating two different composition SiGe buffer layers. A backside-illuminated photodetector has been fabricated with the dark current as low as 3.6 mA/cm2 at 1 V reverse bias. To improve the speed of the photodiode, a device with thinner SiGe buffer layers was demonstrated and achieved 21.5 GHz bandwidth at 1.31 μm, resulting in a record high efficiency-bandwidth product of 12.9 GHz. copyright The Electrochemical Society.