Direct-gap germanium-tin multiple-quantum-well electro-optical devices on silicon or germanium substrates

A semiconductor optical device comprising:

• (a) an active region made up of a multiple quantum well stack having in-plane tensile strained germanium-tin alloy quantum wells and germanium-tin alloy barriers, said quantum well stack having given lattice constants, and wherein the quantum wells have an atomic percentage of tin of 5% to 15%, enabling a direct bandgap to exist between the n=1 conduction subband and the n=1 valence subband of the multiple quantum wells of said stack and wherein said barriers have an atomic percentage of tin of 3% to 6% more than the percentage of tin in the quantum wells and are compressively strained in-plane for producing symmetric strain for the quantum well stack to enable a thick high quality stack to be formed;
• (b) a doped relaxed SiGeSn graded composition lower buffer portion positioned below the stack, grown upon and contacting a substrate selected from the group consisting of Si and Ge;
• (c) a doped relaxed GeSn composition upper buffer portion positioned above the stack, and wherein said upper and lower buffer layers each have a zincblend lattice constant that is halfway between the lattice constant of the wells and the lattice constant of the barriers;
• and
• (d) a first electrode coupled to said upper buffer layer portion and a second electrode coupled to said lower buffer layer portion.