An efficient single-photon source based on low-density InGaAs quantum dots in a photonic-crystal nanocavity is demonstrated. The single-photon source features the effects of a photonic band gap, yielding a single-mode spontaneous emission coupling efficiency as high as beta = 92% and a linear polarization degree up to p = 95%. This appealing performance makes it well suited for practical implementation of polarization-encoded schemes in quantum cryptography.

We demonstrate the growth of indium nitride (InN) nanorods on sapphire by chemical-beam epitaxy without a catalyst. The nanorods are synthesized nearly unidirectionally along the ⟨001⟩ direction and the diameters varied in the range of 20–40nm with In∕N flow ratio. Single-crystalline wurtzite structure is verified by x-ray diffraction and transmission electron microscopy. Raman measurements show that these wurtzite InN nanorods have sharp peaks E2 (high) at 491cm−1 and A1 (LO) at 593cm−1.

The influence of SiO2 and Si3N4 dielectric matrices on the structural, phonon, luminescence and thermal properties of Ge quantum dots (QDs) has been experimentally investigated. Compared with the case of QDs in SiO2 layers, Si3N4 matrix imposes large interfacial surface energy on QDs and enhances their Ostwald ripening rate, appearing to be conducive for an improvement in crystallinity and a morphology change to a more perfectly spherical shape of Ge QDs. Quantum confinement induced electronic structure modulation for Ge QDs is observed to be strongly influenced not only by the QD size but also by the embedded matrix. Both matrix and surface effects offer additional mechanisms to QD itself for controlling the optical and thermal properties of the QDs.

Room-temperature electroluminescence at 1.3 and 1.5 μm from Ge/Si quantum-dot light-emitting diodes is reported. The devices were fabricated in a mesa-type structure, with a silicon oxide layer on the top for surface/sidewall passivation. Different passivation processes were employed. We found that the integrated electroluminescence intensities were relatively less sensitive to temperature, persisting at nearly the same intensity up to RT. The fabricated device shows an internal quantum efficiency of about 0.015% at RT. The improved emission property is attributed to the reduced nonradiative recombination centers due to the surface passivation and thermal treatment.

We propose a novel technique to fabricate a free-standing three-dimensional colloidal crystal by self-assembling the colloidal microspheres with controllable thickness from the air–liquid interface. Highly ordered three-dimensional colloidal crystals are formed by polymethylmethacrylate or polystyrene monodisperse microspheres. We also demonstrate the fabrication technique of the free-standing inversed opals by removing the microspheres using calcination. The free-standing colloidal crystal structures can be used for nano-photonic circuits, white-light LEDs or as a photocatalyst.