Integration of near-infrared light source/detector on Si chips has long been expected to achieve on-chip and/or chip-to-chip optical interconnectivity. However, the indirect band gap of group-IV semiconductor such as Si and Ge remains a challenge especially for photoemission. Although the direct band gap in Si is 3.1 eV above the indirect band gap and the solid solubility limit of Sn in Si is extremely low (0.1%), the Si_1-xSn_x alloys must have a direct band gap for a sufficiently high Sn content, as for Ge_1-xSn_x. From a device perspective, an experimental demonstration of the band gap is desired. However, the relevant optical property for Si_1-xSn_xhas to date not been obtained.

Under such a background, the present paper reports our recent progress in advanced low-temperature crystallizations for Si_1-xSn_x (x: 0–0.4) thin films on various substrates (insulators, Si, Ge, InP, etc.). Composition analyses indicate that approximately 20% of the Sn atoms are substituted into the polycrystalline (or epitaxial) thin films grown on an insulator (or Ge(001)) after annealing at 220 ^oC for 5 h. By using InP(001) substrates, the Sn content could raise up to about 40%. Comparison of the band gap with the calculated values and new applications, such as Si_1-xSn_x-source tunnel field effect transistors and thermoelectric generator, will be discussed.

Acknowledgments

This work was partially supported by Grants-in-Aid for Scientific Research (S) (Grant No. 26220605) and Young Scientists (A) (Grant No. 17H04919) from JSPS in Japan and PRESTO (Grant No. JPMJPR15R2) from JST in Japan.