Gas Source Techniques for Molecular Beam Epitaxy of Highly Mismatched Ge Alloys

Abstract

Ge and its alloys are attractive candidates for a laser compatible with silicon integrated circuits. Dilute germanium carbide (Ge_1−xC_x) offers a particularly interesting prospect. By using a precursor gas with a Ge₄C core, C can be preferentially incorporated in substitutional sites, suppressing interstitial and C cluster defects. We present a method of reproducible and upscalable gas synthesis of tetrakis(germyl)methane, or (H₃Ge)₄C, followed by the design of a hybrid gas/solid-source molecular beam epitaxy system and subsequent growth of defect-free Ge_1−xC_x by molecular beam epitaxy (MBE). Secondary ion mass spectroscopy, transmission electron microscopy and contactless electroreflectance confirm the presence of carbon with very high crystal quality resulting in a decrease in the direct bandgap energy. This technique has broad applicability to growth of highly mismatched alloys by MBE.