Tunable band structure in diamond–cubic tin–germanium alloys grown on silicon substrates

Novel chemical methods based on deuterium-stabilized Sn hydrides and ultra-high-vacuum chemical vapor deposition were used to grow SnxGe1−x alloys directly on silicon. Device-quality, strain-free films with a Sn-fraction as high as x=0.2 were obtained. The optical properties provide evidence for a well-defined Ge-like band structure. In particular, the direct band gap E0 is reduced to a value as low as 0.41 eV for Sn0.14Ge0.86. The growth of these high-optical quality infrared materials creates entirely new opportunities for band gap engineering on Si.