Conducting micro-and nanotubes and free-standing flexible helical microcoils have been fabricated from strained Ge x Si 1−x /Si heterolayers. The fabrication technique was based on self-rolling of a thin highly strained epitaxial Ge x Si 1−x /Si bifilm detached from the substrate by selective etching of a sacrificial layer in a roll-shaped tube. The obtained tube diameters varied from 10 nm to 13 µm, depending on the thickness and lattice mismatch of the GeSi/Si bilayer. GeSi/Si tubes and helical coils, up to 70 nm in diameter, exhibit good conducting properties and high mechanical strength.

We report an investigation of GeSn-based p-i-n photodiodes with an active GeSn layer that is almost fully strained. The results show that (a) the response of the Ge/GeSn/Ge heterojunction photodiodes is stronger than that of the reference Ge-based photodiodes at photon energies above the 0.8 eV direct bandgap of bulk Ge (<1.55 μm), and (b) the optical response extends to lower energy regions (1.55–1.80 μm wavelengths) as characterized by the strained GeSn bandgap. A cusp-like spectral characteristic is observed for samples with high Sn contents, which is attributed to the significant strain-induced energy splitting of heavy and light hole bands. This work represents a step forward in developing GeSn-based infrared photodetectors.

We report the observation of mid-infrared room-temperature electroluminescence from a p-i-n Ge/Ge0.922Sn0.078/Ge double heterostructure diode. The device structure is grown using low-temperature molecular beam epitaxy. Emission spectra under various injection current densities in the range of 318 A/cm2–490 A/cm2 show two distinct profiles peaked at 0.545 eV (2.275 μm) and 0.573 eV (2.164 μm), corresponding to indirect and direct bandgaps of the Ge0.922Sn0.078 active layer, respectively. This work represents a step forward towards the goal of an efficient direct-bandgap GeSn light-emitting device on a Si substrate by incorporating higher Sn content of 7.8% in a diode structure that operates at lower current densities.

We report an investigation on GeSn p-i-n waveguide photodetectors grown on a Ge-buffered Si wafer. In comparison with a reference Ge detector, the GeSn detector shows an enhanced responsivity in the measured energy range, mainly attributed to the smaller bandgap caused by Sn-alloying. Analysis of the quantum efficiency indicates that increasing the Sn content in the active layers can significantly shorten the required device length to achieve the maximum efficiency. The present investigation demonstrates the planar photodetectors desired for monolithic integration with electronic devices.