Efficient coupling to integrated high-quality-factor cavities is crucial for the employment of germanium quantum dot (QD) emitters in future monolithic silicon-based optoelectronic platforms. We report on strongly enhanced emission from single Ge QDs into L3 photonic crystal resonator (PCR) modes based on precise positioning of these dots at the maximum of the respective mode field energy density. Perfect site control of Ge QDs grown on prepatterned silicon-on-insulator substrates was exploited to fabricate in one processing run almost 300 PCRs containing single QDs in systematically varying positions within the cavities. Extensive photoluminescence studies on this cavity chip enable a direct evaluation of the position-dependent coupling efficiency between single dots and selected cavity modes. The experimental results demonstrate the great potential of the approach allowing CMOS-compatible parallel fabrication of arrays of spatially matched dot/cavity systems for group-IV-based data transfer or quantum optical systems in the telecom regime.

We report on the design, fabrication and optical characterization of bichromatic photonic crystal cavities in thin silicon membranes, with resonances around 1.55 µm wavelength. The cavity designs are based on a recently proposed photonic crystal implementation of the Aubry-André-Harper bichromatic potential, which relies on the superposition of two one-dimensional lattices with noninteger ratio between the periodicity constants. In photonic crystal nanocavities, this confinement mechanism is such that optimized figures of merit can be straightforwardly achieved, in particular an ultra-high-Q factor and diffraction-limited mode volume. Several silicon membrane photonic crystal nanocavities with Q-factors in the 1 million range have been realized, as evidenced by resonant scattering. The generality of these designs and their easy implementation and scalability make these results particularly interesting for realizing highly performing photonic nanocavities on different materials platforms and operational wavelengths.

The revival of interest in Ge1−xSnx alloys with x ≥ 10% is mainly owed to the recent demonstration of optical gain in this group-IV heterosystem. Yet, Ge and Sn are immiscible over about 98% of the composition range, which renders epilayers based on this material system inherently metastable. Here, we address the temperature stability of pseudomorphic Ge1−xSnx films grown by molecular beam epitaxy. Both the growth temperature dependence and the influence of post-growth annealing steps were investigated. In either case we observe that the decomposition of epilayers with Sn concentrations of around 10% sets in above ≈230 °C, the eutectic temperature of the Ge/Sn system. Time-resolved in-situ annealing experiments in a scanning electron microscope reveal the crucial role of liquid Sn precipitates in this phase separation process. Driven by a gradient of the chemical potential, the Sn droplets move on the surface along preferential crystallographic directions, thereby taking up Sn and Ge from the strained Ge1−xSnx layer. While Sn-uptake increases the volume of the melt, single-crystalline Ge becomes re-deposited by a liquid-phase epitaxial process at the trailing edge of the droplet. This process makes phase separation of metastable GeSn layers particularly efficient at rather low temperatures.

We report on the fabrication and characterization of silicon-on-insulator (SOI) photonic crystal slabs (PCS) with commensurately embedded germanium quantum dot (QD) emitters for near-infrared light emission. Substrate pre-patterning defines preferential nucleation sites for the self-assembly of Ge QDs during epitaxial growth. Aligned two-dimensional photonic crystal slabs are then etched into the SOI layer. QD ordering enhances the photoluminescence output as compared to PCSs with randomly embedded QDs. Rigorously coupled wave analysis shows that coupling of the QD emitters to leaky modes of the PCS can be tuned via their location within the unit cell of the PCS.

Figure 14. Four fuzzy rules extracted from data for explanation modeling of cooling capacity termed as "KL_P_SCHACHT."