Techniques are described for forming a waveguide photodetector. In one example, a method of forming a waveguide photodetector includes forming a waveguide on a substrate, e.g., silicon on insulator, depositing a first oxide coating over the waveguide and on the SOI substrate, creating a seed window through the first oxide coating to a bulk silicon layer of the SOI substrate, depositing a photodetector material into the seed window and on top of the first oxide coating over the waveguide, depositing a second oxide coating over the photodetector material and over the first oxide coating deposited over the waveguide and on the SOI substrate, and applying thermal energy to liquefy the photodetector material.