A germanium metal-semiconductor-metal (MSM) photodetector is fabricated by growing crystalline germanium from an amorphous silicon seed, supported by an amorphous substrate, at a temperature of about 450° C. In this fabrication, crystalline Ge is grown via selective deposition in geometrically confined channels, where amorphous silicon is disposed as the growth seed. Ge growth extends from the growth seed along the channels to a lithographically defined trench. The Ge emerging out of the channels includes crystalline grains that coalesce to fill the trench, forming a Ge strip that can be used as the active area of a photodetector. One or more Schottky contacts can be formed by a thin tunneling layer (e.g., Al2O3) deposited on the Ge strip and metal contracts formed on the tunneling layer.