Patent ID: 8119904

Claim:
A method for fabricating a multi-junction photovoltaic device, the method comprising: forming a dielectric layer on a silicon substrate; forming channels within the dielectric layer, wherein the channels extend through the dielectric layer exposing an upper portion of the silicon substrate; after forming the channels, epitaxially growing, a silicon-germanium material from Si and Ge deposition sources up from the silicon substrate through the channels; grading up the silicon-germanium material; after a given amount of silicon-germanium material has been deposited on a top surface of the dielectric layer, forming a pure germanium layer on the silicon-germanium material that has been graded up, the pure germanium layer transitioning into the silicon-germanium material; recrystallizing at least the pure germanium layer, where a crystalline orientation of the silicon substrate is used as a re-crystallization template for at least the pure germanium layer; forming a first photovoltaic sub-cell comprising a first plurality of doped semiconductor layers on the pure germanium layer; and forming at least a second photovoltaic sub-cell comprising a second plurality of doped semiconductor layers on the first photovoltaic sub-cell that is on the pure germanium layer.