Detectors based on such Ge(Sn) alloys of the formula Ge.sub.1-xSn.sub.x (e.g., 0<x<0.01) have increased responsivity while keeping alloy scattering to a minimum. Such small amounts of Sn are also useful for improving the performance of the recently demonstrated Ge-on-Si laser structures, since the addition of Sn monotonically reduces the separation between the direct and indirect minima in the conduction band of Ge. Thus, provided herein are Ge(Sn) alloys of the formula Ge.sub.1xSn.sub.x, wherein x is less than 0.01, wherein the alloy is optionally n-doped or p-doped; and assemblies and photodiodes comprising the same, and methods for their formation.
STATEMENT OF GOVERNMENT FUNDING
 The invention described herein was made in part with government support under grant number DOD AFOSR FA9550-06-01-0442 awarded by the United States Air Force (MURI program); grant number DE-FG36-08GO18003 awarded by the Department of Energy; and grant number DMR-0907600, awarded by the National Science Foundation. The United States Government has certain rights in the invention.