Strain in Si or Ge from the edge forces of epitaxial nanostructures

The introduction of strain in semiconductors is a well-known technique exploited in microelectronics to increase their mobility and thus to enhance the performance of silicon-based electronic devices. Moreover, tensile strain is one feasible route towards converting Ge into an efficient light emitter. Here we show how the application of local strain via nanopatterning opens a wider parameter space for strain engineering in semiconductors of the Si/Ge material system. The general approach relies on the top-down fabrication of SiGe stressors realized by electron-beam lithography (EBL) and reactive-ion etching (RIE). Specifically, compressive strain can be locally applied to pure Si and tensile strain can be applied to pure Ge. Raman spectroscopy is used to investigate the strain induced in Si or Ge bulk like substrates. Furthermore, the realization of stressors on micro-bridges demonstrates higher achievable strain level if compared to the attached bulk-like case. The strain enhancement is due to the high sharing of elastic energy in between the nanostructures and the bridges. The SiGe stressor approach hence presents a CMOS compatible alternative for strain creation in Si, Ge and SiGe

Selective growth of fully relaxed GeSn nano-islands by nanoheteroepitaxy on patterned Si(001)

In this letter, we explore in detail the potential of nanoheteroepitaxy to controllably fabricate high quality GeSn nano-structures and to further improve the crystallinity of GeSn alloys directly grown on Si(001). The GeSn was grown by molecular beam epitaxy at relatively high temperatures up to 750 degrees C on pre-patterned Si nano-pillars embedded in a SiO2 matrix. The best compromise between selective GeSn growth and homogenous Sn incorporation of 1.4% was achieved at a growth temperature of 600 degrees C. X-ray diffraction measurements confirmed that our growth approach results in both fully relaxed GeSn nano-islands and negligible Si interdiffusion into the core of the nanostructures. Detailed transmission electron microscopy characterizations show that only the small GeSn/Si interface area reveals defects, such as stacking faults. Importantly, the main part of the GeSn islands is defect-free and of high crystalline quality. The latter was further demonstrated by photoluminescence measurements where a clear redshift of the direct CC-CV transition was observed with increasing Sn content