Synthesis of Superhard Thin Films and Coatings Based on Light Elements

摘要

Superhard dielectric and optoelectronic materials in the Si-C-Al-N si-B-O-N and Zr-B/Ga-N systems were prepared as thin films via novel CVD and MBE routes. SiC and AlN, normally insoluble in each other below 2000 deg C are combined to form single phase SiCAlN by gas source MBE of SiH3CN and Al atoms at 75000. The growth of epitaxial material takes place on 6H SiC and Si(111). Commensurate heteroepitaxy between Si(111) and SiCAIN is facilitated by the presence of a crystalline (Si-O-Al-N) oxide at the Si interface. The bandgap of SiCAlN is 3.2 eV and average hardness is 25 Gpa. Superhard metal borides such as ZrB2 and ternary analogs have been grown as perfectly epitaxial layers on Si(111). These materials in turn are used as totally reflective and lattice- matched buffer layers for integration of light emitting nitrides (GaN and AlGaN) with Si. UHV-CVD growth of single-phase Ge(1-x-y)Si(x) SN(y) semiconductors is conducted for the first time on Si(1OO). These materials exhibit tunable band gaps and possess lattice constants above and below that of Ge. The fabrication of Ge(1-x-y)Si(x)Sn(y) makes it possible to decouple strain and band gap engineering to achieve unique structures that lead to novel photonic devices based entirely on group IV materials (covering a wide range of operating wavelengths in the IR). Growth of random Ge(1-x)Sn(x) alloys and related ordered structures has been achieved directly on Si(100). Optical characterizations show a Ge like band structure. The band gaps and critical point energies are reduced monotonically with Sn content indicating that band gap engineering has been obtained in this system.