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.
We report on the realization of high-Q/V
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,
defined from the superposition of two one-dimensional lattices with a non-integer ratio
between their 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
have been realized with measured
Q-factors in the 1 × 106 range, as evidenced by resonant scattering. The
generality of the proposed designs and their easy implementation and scalability make
these results particularly interesting for realizing highly performing photonic nanocavities on
different material
platforms and operational wavelengths.
Isolated in-plane wires on Si(001) are promising nanostructures for quantum transport applications. They can be fabricated in a catalyst-free process by thermal annealing of self-organized Si1−xGex ...hut clusters. Here, we report on the influence of composition and small substrate miscuts on the unilateral wire growth during annealing at 570 °C. The addition of up to 20% of Si mainly affects the growth kinetics in the presence of energetically favorable sinks for diffusing Ge atoms, but does not significantly change the wire base width. For the investigated substrate miscuts of <0.12°, we find geometry-induced wire tapering, but no strong influence on the wire lengths. Miscuts <0.02° lead to almost perfect quantum wires terminated by virtually step-free {105} and {001} facets over lengths of several 100 nm. Generally, the investigated Si1−xGex wires are metastable: Annealing at ≥600 °C under otherwise identical conditions leads to the well-known coexistence of Si1−xGex pyramids and domes.
The almost completely immiscible PbTe/CdTe heterostructure has recently become a prototype system for self-organized quantum dot formation based on solid-state phase separation. Here, we study by ...real-time transmission electron microscopy the topological transformations of two-dimensional PbTe-epilayers into, first, a quasi-one-dimensional percolation network and subsequently into zero-dimensional quantum dots. Finally, the dot size distribution coarsens by Ostwald ripening. The whole transformation sequence occurs during all stages in the fully coherent solid state by bulk diffusion. A model based on the numerical solution of the Cahn-Hilliard equation reproduces all relevant morphological and dynamic aspects of the experiments, demonstrating that this standard continuum approach applies to coherent solids down to nanometer dimensions. As the Cahn-Hilliard equation does not depend on atomistic details, the observed morphological transformations are general features of the model. To confirm the topological nature of the observed shape transitions, we developed a parameter-free geometric model. This, together with the Cahn-Hilliard approach, is in qualitative agreement with the experiments.
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