Synthesis of silicon-based infrared semiconductors in the Ge-Sn system using molecular chemistry methods

Growth reactions based on a newly developed deuterium-stabilized Sn hydride [(Ph)SnD3] with Ge2H6 produce a new family of Ge-Sn semiconductors with tu nable band gaps and potential applications in high-speed, high-efficiency i nfrared optoelectronics. Metastable diamond-cubic films of Ge1-xSnx alloys are created by chemical vapor deposition at 350 degreesC on Si(100). These exhibit unprecedented thermal stability and superior crystallinity despite the 17% lattice mismatch between the constituent materials. The composition , crystal structure, electronic structure, and optical properties of these materials are characterized by Rutherford backscattering, high-resolution e lectron microscopy, and X-ray diffraction, as well as Raman, IR, and spectr oscopic ellipsometry. Electron diffraction reveals monocrystalline and perf ectly epitaxial layers with lattice constants intermediate between those of Ge and a-Sn. X-ray diffraction in the theta -2 theta mode shows well-defin ed peaks corresponding to random alloys, and in-plane rocking scans of the (004) reflection confirm a tightly aligned spread of the crystal mosaics. R BS ion-channeling including angular scans confirm that Sn occupies substitu tional lattice sites and also provide evidence of local ordering of the ele ments with increasing Sn concentration. The Raman spectra show bands corres ponding to Ge-Ge and Sn-Ge vibrations with frequencies consistent with rand om tetrahedral alloys. Resonance Raman and ellipsometry spectra indicate a band-gap reduction relative to Ge. The IR transmission spectra suggest that the band gap decreases monotonically with increasing Sn fraction. The synt hesis, characterization, and gas-phase electron diffraction structure of (P h)SnD3 are also reported.