Patent ID: 7405465

Claim:
A semiconductor device comprising a layerstack, the layerstack comprising: a first layer of deposited heavily n-doped semiconductor material above a substrate, the first layer at least about 50 angstroms thick; a second layer of semiconductor material which is not heavily n-doped, wherein the semiconductor material of the second layer is a silicon-germanium alloy that is at least 10 at % germanium, the second layer at least about 100 angstroms thick, wherein the second layer is above and in contact with the first layer; and a third layer of deposited semiconductor material which is not heavily n-doped above and in contact with the second layer, wherein the semiconductor material of the third layer is silicon or a silicon-germanium alloy that is less than 10 at % germanium, wherein the first, second, and third layers reside in a semiconductor device.