Kanna Aoki

Demonstration of high-Q (>8600) three-dimensional photonic crystal nanocavity embedding quantum dots

The authors report on an experimental demonstration of coupling of quantum dots with a point-defect nanocavity in woodpile three-dimensional (3D) photonic crystal (PhC) with the highest quality (Q) factor among those for 3D PhC cavities. The Q factor of more than 8600 was achieved by stacking 25 layers using a micromanipulation technique. The size of the square-shaped defect cavity was optimized to tune the cavity mode to the midgap frequency of the complete photonic bandgap to achieve high Q.

Effects of rapid thermal annealing on the emission properties of highly uniform self-assembled InAs∕GaAs quantum dots emitting at 1.3μm

The authors report the effects of rapid thermal annealing (RTA) on the emission properties of highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3μm grown on GaAs substrate by metal organic chemical vapor deposition. Postgrowth RTA experiments were performed under N2 flow at temperatures ranging from 600to900°C for 30s using GaAs proximity capping. Surprisingly, in spite of the capping, large blueshifts in the emission peak (up to about 380meV at 850°C) were observed (even at low annealing temperatures) along with enhanced integrated photoluminescence (PL) intensities. Moreover, pronounced peak broadenings occurred at low annealing temperatures (<700°C), indicating that RTA does not always cause peak narrowing, as is typically observed with traditional QDs with large inhomogeneous PL linewidths. The mechanism behind the large peak blueshift was studied and found to be attributed to the as-grown QDs with large size, which cause a larger dot-barrier interface and greater strain in and near ...

Practical approach for a rod-connected diamond photonic crystal operating at optical wavelengths

Production of a rod-connected diamond (RCD) photonic crystal structure in a semiconductor material is proposed. Periodic shifting of only one building block can create a complicated three-dimensional network, with a RCD structure exhibiting a full bandgap as wide as 0.20 on a gap/midgap (Δω/ωM) basis. A point defect cavity in the structure sustains single-mode resonance throughout the operative range because of its low symmetry. The resonant mode’s highest quality factor (Q-factor) was calculated as 1.5×104 for a crystal of 11.5ax×4.25ay×12az for ai (i=x,y,z) representing three axes’ period lengths.

Arrayed 3D Photonic Crystals for Optical Communication Wavelengths

Only summary form given. An array of 3D photonic crystals for infrared wavelengths of 1.3-1.6 mum is assembled on a chip by micromanipulation. Each of the crystals possesses a different structure with various in-plane period, number of layers, and defect sizes. Photoluminescence measurements showed that emissions from an active layer were suppressed in the regions of photonic bandgaps, whereas sharp emission originates from point defects were clearly observed. Emission wavelengths and their quality factors changed through the differences in crystal geometries.

Fabrication of Rod-Connected Diamond Structures at Optical Wavelengths by Micromanipulation

A rod-connected diamond structure is known to exhibit the largest full photonic bandgap. However, its seemingly intricate structure turned off researchers motivation for fabrication. In this paper, we propose a novel fabrication technology for optical rod-connected diamond photonic crystals by uniting angled dry etching method with micromanipulation. Although, diamond structures have been found to be a good candidate for a full photonic-bandgap structure, there are no cases of their accurate creation with semiconductor materials at optical wavelengths. The main reason researchers give up synthesizing the structures is their cross-linked networks. Because conventional integrated circuit fabrication techniques have been developed intensively for one-dimensional processing, experimentalists react in a negative way to structures having nonvertical frameworks. Thus, theorists have been trying to deform diamond structures to suit the convenience of experimentalists. Unfortunately, those alternative structures are often more difficult to fabricate and accompanied by a reduction of bandgaps. A few structures, such as Yablonovite, woodpile, and MIT structures- have been successfully realized for optical wavelengths using microelectronic fabrication technology. However, the Yablonovite and MIT structures seem to be technologically demanding; thus, succeeding reports have not appeared. Also, their maximum gap/midgap ratios (Deltaomega/omegaM) respectively diminish to 2-3% and 23% from the best value of 30% for a strict diamond structure (i.e., a dielectric-rod-connected diamond structure). The woodpile structures simpler formation (cross stack of rods) is rather stimulating for experimentalists, and various approaches have been proposed for this structure. However, deviation from the strict diamond structure diminishes the maximum Deltaomega/omegaM to 18%. Not only dielectric-rod-connected diamond structures, but their inversed structures made of air rods in dielectric background also show a large Deltaomega/omegaM, as large as 28%. We have recently realized that air-rod-connected diamond structures in dielectric materials can be relatively easily obtained by combining angled dry etching with micromanipulation. In our approach, a diamond structure is initially sliced into four planes orthogonal to the (100) direction. Each slab has openings aligned into a square lattice on a surface. Angled holes are etched twice through these openings by inductively coupled plasma reactive-ion etching (ICP-RIE) so that the neighboring rods join at the rear surface. Then each plate is assembled into 3D structures by micromanipulation. We used to use polystyrene microspheres and matching holes prepared on a plate for automatic alignment. With this alignment technique, plates are automatically placed into proper positions with a structural error of within 50 nm, and a series of assemblies can be completed within one hour. In this study, we employed a combination of square columns etched on a wafer and matching notches prepared around plates for more rapid assembly. This method reduces operating time to 15 minutes while retaining the structural errors within 50 nm. Air-rod-connected diamond photonic crystals obtainable by the proposed procedure are expected to exhibit a maximum Deltaomega/omegaM of 20% for a refractive index of the dielectric material of 3.4. The reduction of the gap seems to be caused by parts of rods sticking out from a circular joint. However, a 20% complete gap is still higher than that of the woodpile structure, and sufficient for the utilization of photonic crystals in various devices. Also, the techniques of angled dry etching and refined micromanipulation open up the possibility of designing new structures, waveguides, or defects, and high achieving productivity. These are inevitable features for the mass production of functional photonic crystal devices

Formation of self-assembled InAs/GaAs quantum dots with an ultranarrow photoluminescence linewidth of /spl sim/11 meV by rapid thermal annealing

We report the effects of rapid thermal annealing on emission properties of highly uniform self-assembled InAs/GaAs quantum dots grown by metalorganic chemical vapor deposition and demonstrate an ultranarrow linewidth of /spl sim/11 meV by the annealing.