The growth of a single-crystal alloy layer of germanium and silicon on a very high resistivity silicon substrate is a new and unexplored technique for optical waveguiding in the 1.3 to 1.6 micron infrared wavelength range. A related, but more speculative approach, is the epitaxial growth of crystalline tin- silicon alloys on silicon, which has never been done. SnSi would allow a lower percentage of tin in the alloy than the percentage of Ge in GeSi to achieve a given amount of refractive index increase. The advantages of these alloys as waveguides include very low waveguide propagation loss and compatibility with Si processing. In Phase I Spire Corporation will grow symmetric Si/GeSi/Si and Si/SnSi/Si waveguide structures using a double heteroepitaxy of crystalline GexSi(1-x) or SnxSi(1-x) on (100) silicon, followed by an epitaxial silicon layer on the alloy, and to perform optical waveguide tests on the material at a wavelength of 1.3 microns. The thickness of the alloy layer will be varied from 1 to 10 microns and x will be varied from 0.05-0.20. They hope to show from the waveguide tests that losses are low, and the TE0 mode is not cut off at submicron thickness. The general goals for Phase II are to build upon the Phase I results to develop active, guided-wave electro-optic devices.
