High-quality factor photonic crystal nanocavities probed with SiGe/Si self-assembled islands

We report on the experimental analysis at room temperature of high-quality factor (Q) two-dimensional photonic crystal nanocavities. SiGe/Si self-assembled islands are embedded as active internal sources inside the photonic crystal slab. In this work we focus on longitudinal nanocavities design, i.e. L3 and L4 type cavities. A tuning of the L3 quality factor is achieved by fine modification of hole position at the edges of the cavity. Quality factor values as large as 15 000, United by spectrometer resolution, are measured with the internal source method. We show that the measured quality factors are strongly affected by the optical pumping of the cavity. A variation by one order of magnitude of Q values is observed as a function of the pump power density. These investigations show that the external pumping of cavities required to probe the photonic crystal defect modes introduces by itself additional non negligible loss mechanisms in the cavity. It leads to severe limitations on the Q factors that can be measured experimentally. A strong luminescence signal enhancement by two orders of magnitude associated with the islands embedded in the nanocavities is observed.