Stimulated emission in nanocrystalline silicon superlattices

We studied the conditions under which optical gain is measured in nanocrystalline silicon (nc-Si) using the variable stripe length method. Waveguide samples have been produced by magnetron sputtering of alternating layers of Si and SiO2, followed by high temperature annealing. No optical gain was observed under continuous wave pumping conditions. Under high intensity pulsed excitation, a superlinear fast (10 ns) recombination component yielding an optical gain up to 50 cm−1 has been independently measured in two different laboratories. A control experiment confirmed that the presence of nc-Si is necessary to achieve gain in our structures.