Fabrication of Nanostructures: Quantum Dots and Photonic Crystals

In order to create nanosystems which enable us to manipulate individual electrons or photons, we develop fabrication technologies for nanostructures such as quantum dots (QDs) or photonic crystals (PhCs) by employing metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or electron beam lithography. Recently, we have succeeded in fabricating state-of-the-art InAs/GaAs QDs for telecommunications and quantum information device applications, as well as III-nitride nanostructures (QDs and nanowires). In addition, we also develop fabrication technologies for 3D PhCs. The world’s highest Q factor (~ 38,500) in a 3D PhC nanocavity and successful lasing from the cavity have been achieved.

(a) Photoluminescence of InAs quantum dot on 1.3μm band
(b) InGaAs/GaAs nanowire array on GaAs substrate
(c) Low density GaAs nanowires on Si substrate

(left) GaN quantum dot on site controlled GaN/AlGaN nanowires
(right) AlN 1D photonic crystal nanocavity

3D photonic crystal and weak coupling regime

Studies on Optoelectronic Properties of Nanostructures, Basic Research on Quantum Information Devices

Electronic/optical properties of QDs or PhCs are experimentally investigated by using sophisticated spectroscopic techniques including a single QD spectroscopy system we developed in-house, which produces world-leading achievements continuously. In this regard, we have successfully observed the relaxation of coupled quantum states. The physics in a coupled QD-photonic crystal nanocavity system has also been studied. In addition, we promote basic research on quantum information devices. We have realized high-performance single photon sources operating at 1.55 mm telecom band, established a quantum key distribution system, and demonstrated secure key distribution over 50 km distance. In addition, a number of results have also been achieved; i.e., single photon LEDs, single photon generation at 200 K from III-nitride QDs, and realization of coherent control of QD excitons.

(a) Density matrix of 2 photon from self-assembled quantum dot
(b) STEM Image of section of nanowire - quantum dot structure and its auto-/cross correlation

(left) exiton - biexiton luminescence
(right) Exprimetal result and theorical calculation of exiton spectrum

Luminescence spectrum of Quantum dot - Photonic crystal combination system

Development of Nano Optoelectronic Devices and LSI-Photonics Fusion Technologies

Our research is directed toward advanced nano-photonic devices incorporating QDs or PhCs. In particular, by working in close collaboration with industry, we have developed high-quality QD lasers as well as QD-based green lasers. Also, high-quality PhC nanocavity-based single QD lasers and QD-embedded 3D PhC nanocavities have been successfully fabricated. In addition, next-generation photonics-electronics convergence system technologies featuring high-efficiency light sources on silicon substrates are also under development. Among them, we have realized telecom-band 1.3 mm QD lasers on silicon substrates by employing wafer bonding techniques.

(left) The structure of Quantum dot Fabry-Perot laser
(right) Property of current - optical output

(left) Quantum Dot - Phtonic Crystal nanolaser on Silicon substrate
(right) Fabry-Perot Quantum dot laser

Green Electronics and Photonics

For the purpose of realizing a green information society, we are focusing on research and development of high-efficiency energy conversion devices and flexible electronics devices. Especially, fabrication technologies for high-performance QD solar cells have been developed by using sophisticated crystal growth techniques, and the possibility of ultrahigh efficiency (75 %) multilevel intermediate band solar cells has been theoretically predicted. Also, we develop fabrication technologies of organic transistors for flexible electronics applications. Outstanding results have been achieved, including low-voltage-operating / high-speed organic CMOS circuits.

(left) Light switching by using cavity mode and quantum dot
(right) The change of luminescence spectrum by cavity stark effect

Inkjet printed organic transistor

(left) Quantum Dot Solar Cell with 4 intermidiate band
(right) Flexible Quantum Dot Solar Cell