Hsiang-Szu Chang

Self-assembled free-standing colloidal crystals

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.

Single photon emission from an InGaAs quantum dot precisely positioned on a nanoplane

This work demonstrates single photon emissions from a site-controlled quantum dot (QD) grown on a self-constructed nanoplane. The size of the nanoplane on the micron-sized multifacet structure is accurately controlled by a low surface reducing rate (∼16nm∕min). Single QD spectral lines were resolved and identified. The antibunching behavior reveals that single photons are emitted from the positioned QD.

Optical properties of indium nitride nanorods prepared by chemical-beam epitaxy

The optical properties of indium nitride nanorods grown by chemical-beam epitaxy are investigated by photoluminescence (PL) and Raman spectroscopy. The PL peaks show a blue shift from 0.69 to 0.79 eV, which is associated with a decrease in the size of the nanorods from 40 to 5 nm. Judging from the Raman spectra and transmission electron diffraction of these nanorods, it can be concluded that the quantum size effect is the most likely factor causing the PL shift, rather than the strain or Moss–Burstein effects.

Growth of low density InGaAs quantum dots for single photon sources by metal?organic chemical vapour deposition

We report the preparation of low density self-assembled InGaAs on GaAs grown by metal–organic chemical vapour deposition for single photon sources. Through using a set of optimized growth parameters, including the arsine partial pressure, total coverage of quantum dots, and growth temperature, high optical quality quantum dots with density as low as 5 × 106 cm−2 have been obtained. Using local optical excitation through a sub-micron aperture of a single quantum dot, its spectral lines associated with the exciton, biexciton, multi-exciton, and charged exciton have been resolved and identified. Photon correlation measurements show that the single quantum dot can successfully emit antibunched photons.

High extractive single-photon emissions from InGaAs quantum dots on a GaAs pyramid-like multifaceted structure.

This work investigates the single-photon emissions from self-assembled InGaAs quantum dots that are grown on an apex plane of a GaAs pyramid-like multifaceted structure. The number of QDs on a multifaceted structure is estimated by scanning electron microscopy. Single-exciton emissions from individual quantum dots are examined by micro-photoluminescence and by making photon correlation measurements. This experiment demonstrates the improvement of the single-photon extraction efficiency as quantum dots are grown on a reduced apex plane of a multifaceted structure.

Enhancing luminescence efficiency of InAs quantum dots at 1.5μm using a carrier blocking layer

The authors report an effective way to enhance the optical efficiency of InAs quantum dots (QDs) on GaAs emitting at the wavelength of 1.5μm. It is found that the loss of holes from QDs to their proximity via the high indium composition InGaAs overgrown layer, which is necessary for achieving long wavelength emission, is the origin of photoluminescence intensity degradation at high temperature. Inserting a 4nm thick Al0.45Ga0.55As layer, acting as a carrier blocking layer, into the GaAs capping matrix can improve the room temperature photoluminescence peak intensity by five and two times for the ground and first excited states, respectively.

Photoluminescence of self-assembled InAs quantum dots embedded in photonic crystal nanocavities with shifted air holes

This study investigates the photoluminescence for self-assembled InAs quantum dots embedded in photonic crystal nanocavities as two of the air holes nearest the H1 cavity were shifted. A rapid decrease of resonant wavelength and quality factor for the cavity modes, in which the electric field patterns extended in the shifting direction, were found as the shift increased from 0.2 to 0.4 lattice constants. This phenomenon is interpreted as being caused by the formation of two point defects between the nearest and second nearest air holes.

Single Photon Emission From an InGaAs Quantum Dot Precisely Positioned on a Nano-Plane

This work demonstrates single photon emissions from a site-controlled quantum dot (QD) grown on a self-constructed nano plane. The size of the nano plane on the micron-sized multi-facet structure is accurately controlled by a low surface reducing rate (~16 nm/min). Single QD spectral lines were resolved and identified. The anti-bunching behavior reveals that single photons are emitted from the positioned QD.

Low‐density quantum dots embedded in photonic‐crystal nanocavities for single‐photon generations

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 photonic band gap, yielding a single‐mode spontaneous emission coupling efficiency as high as β=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.

Single photon sources based on single InGaAs quantum dots

In this report, we present the fabrication of single photon source based on InGaAs QD grown by metal-organic chemical vapor deposition. To enhance the performance of QD single-photon emitters through the Purcell effect, QD is incorporated into an optical cavity. High efficiency single photon source by coupling single QD into a photonic crystal nano-cavity is realized