Abstract
Ge and its alloys are attractive candidates for a laser compatible with silicon integrated circuits. Dilute germanium carbide (Ge1−xCx) 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 Ge1−xCx 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.
Highlights
Ge and its alloys have kindled great interest for faster field effect and tunneling transistors, and even more interest as the possible “holy grail” CMOS-compatible laser [1,2,3,4,5,6]
A time study showed that slowly stirring for 8–12 h leads to almost complete conversion with 95% yield at a 2.2 mmolar scale, and 85% yield at a five-fold scale
It is important to note that C clusters can act as Frank-Read sources, which would generate large dislocation networks, but analysis of the TEM shows no signs of dislocations
Summary
Ge and its alloys have kindled great interest for faster field effect and tunneling transistors, and even more interest as the possible “holy grail” CMOS-compatible laser [1,2,3,4,5,6]. Tensile Ge and optically pumped Ge1−x Snx lasers have been demonstrated, but these showed very high thresholds due to adverse band structures [3,4,6]. Dilute germanium carbide (Ge1−x Cx ) with x ≈ 0.01 has recently been predicted to show a strongly direct bandgap and favorable band alignments, with optical emission expected to rival that of III–V semiconductors [7]. C atoms are much smaller and more electronegative than their Ge host, analogous to N in GaAs. C atoms are much smaller and more electronegative than their Ge host, analogous to N in GaAs This has unusual effects on the band structure of the alloy. The virtual crystal approximation fails to predict semiconductor properties such as bandgap and band alignment. Available online: https://www.pfeiffervacuum.com/en/know-how/introduction-to-vacuum-technology/fundamentals/conductance/ (accessed on 21 November 2016).
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