2, Structured Materials Industries, Inc., Piscataway, New Jersey, United States
Silicon Germanium Tin (SiGeSn) is an emerging class of group IV alloy that is opening new pathways for the development of integrated photonics on microelectronics platform. SiGeSn has several appealing features such as higher mobility compared to silicon, the ability to alter the band gap along with indirect-direct transitions and the ability to engineer the lattice constant independent of the band gap and grow it on various substrates. Thus, SiGeSn can lead towards promising near- and mid-infrared optoelectronic devices which will create plenty of opportunities in the fields of high performance computing networks and energy trapping and conversion. Semiconductor-on-insulator technology is of interest as its development can lead to devices such as high mobility transistors and higher frequency applications. Sapphire is one good choice for an insulator substrate as it has a transparency window up to 6 µm and it offers high-frequency parasitic capacitance, radiation hardness and reduction of latch-up in CMOS structures. Silicon dioxide is another popular choice for insulator because of its low dielectric loss and low loss tangent.
In this work, SiGeSn films were deposited on three different substrates i.e c-plane sapphire, 100 nm silicon dioxide coated silicon (100) and silicon (100). The films were deposited using plasma enhanced chemical vapor deposition (PECVD) technique, as it offers a cost effective and low temperature route for deposition of the films. The composition of the films was varied by varying the input precursor flow rates of Si, Ge and Sn. RBS analysis of the films revealed that Sn and Si concentrations through 10% and 25% respectively were realized. From XRD analysis, it was observed that the deposited films were polycrystalline in nature irrespective of the substrate used. Singular peaks were observed corresponding to the standard (111), (220), (311) and (004) Ge peaks which indicate that the deposited films were cubic in nature. It was observed that films deposited on sapphire mostly grew in the (111) orientation. For films deposited on silicon dioxide, growth took place majorly in the (111) and (220) orientation. For films deposited on silicon (100) substrate, the films adopted the (111) and (004) orientation substantially. It was also observed that the position of the XRD peaks change to a lower or higher angle depending on the Sn and Si concentrations present in the films. However, the peak position did not change for films with same composition grown on different substrates. This corroborates with the RBS analysis that the composition does not change with change in substrate. From Raman spectroscopy, peaks correlating with Ge-Ge, Ge-Sn, Si-Sn and Si-Ge bonds were observed for the films deposited on the various substrates. This confirms the formation of the ternary alloy in the deposited films. The peak positions either red shifted or blue shifted depending upon the film composition.