From rolled-up Si microtubes to SiOx/Si optical ring resonators

We present a fabrication technique to realize SiO"x/Si optical ring resonators based on rolled-up Si microtubes. The strain gradient inside a partially strain-relaxed Si film on a relaxed Ge buffer is employed to roll up the released Si or SiO"x/Si layers into microtubes by selectively etching away the Ge relaxed buffer. After annealing the SiO"x/Si tubes at 850^oC, the hybrid microtubes emit light in the visible spectral range at room temperature. Optical resonant modes are observed in the freestanding hybrid tubes and are found to sensitively depend on the structural uniformity. Finally, we demonstrate positioning of freestanding SiO"x/Si tubes on a Si substrate by using standard lithographic techniques.