NAKANO and TANEMURA Laboratory, Dept. of Electrical Engineering

Current Research Projects 2017 (Japanese)

1. Monolithically Integrated Photonic Circuits with Novel Functions
Y. Nakano, T. Tanemura, M. Sugiyama, S. Ghosh, E. Kato, M. A. Kazi, M. Fukuda, R. Tang, J. Zhang, R. Kobayashi, Y. Kosugi, K. Suga, K. Okawa, Y. Kono, T. Suganuma, S. Onoduka, M. Ogasawara, R. Tanomura, T. Fukuya, and Y. Nakano

 Monolithically integrated semiconductor optical devices and circuits are expected to play key roles in advanced optical communication, optical information processing, and optical sensing applications, since they could provide complicated functions and higher performances that cannot be obtained with discrete devices. We are developing and fabricating monolithically integrated photonic circuits with new functions by utilizing compound semiconductors as good materials for active devices, supplemented by silicon as a material with superior manufacturability. In succession from the previous year, we are studying a group of photonic integrated circuits capable of controlling polarization states, such as an asymmetric optical waveguide polarization converter, a polarization combiner/splitter circuit, a polarization analyzer circuit, an arbitrary polarization synthesizer, and a Stokes vector modulation circuit, as well as a group of circuits manipulating optical mode and wavefront, such as a 2 dimensional beam scanner circuit based on an optical phased array and integrated optical amplifiers, an arbitrary unitary conversion optical circuit, and a surface normal electro-optic polymer modulator. Their application to imaging (such as LIDAR) is also investigated.

2. Next Generation Semiconductor Lasers and Semiconductor Light Sources
Y. Nakano, T. Tanemura, M. Sugiyama, R. Taylor, E. Kato, Y. Xiao, P. Zhou, H. Machiya, K. Feng, M. Watanabe, J. Zhang, and T. Kitatani

 We are investigating next generation semiconductor lasers that should contribute to optical communication, optical information processing, and optical sensing applications. We are also studying semiconductor micro/nano light emitters with low power consumption for optical interconnect applications between or inside racks and chips. Last year we succeeded in low temperature current injection losing and room temperature optical pumping losing of capsule-shaped micro metallic cavity lasers. In this fiscal year, we are aiming at room temperature current injection continuous wave losing of such micro lasers, and are analyzing, designing, and fabricating coupling structures to output waveguides. In parallel, we are researching metal-organic vapor phase epitaxy (MOVPE) technologies for integrating distributed feedback (DFB)/distributed Bragg reflector (DBR) lasers, electro-absorption modulators, and passive optical devices in an array form.

3. Ultra-high Efficiency Solar Cells by Compound Semiconductor Quantum Structures
Y. Nakano, M. Sugiyama, K. Watanabe, T. Tanemura, H. Sodabanlu, E. Kato, W. Yanwachirakul, K. Toprasartpong, H. Xu, S. Saito, and M. Asami

We are studying and developing photovoltaic cells with ultra-high efficiencies toward 50%, based on compound semiconductor quantum micro structures grown by metal organic vapor phase epitaxy (MOVPE). More specifically, high efficiency cells of multiple junction tandem and intermediate band types are being investigated. In this fiscal year, ultra-high speed growth techniques, doping technologies for low resistance tunnel junctions, low barrier cell structures utilizing InGaAsN, carrier transport phenomena in quantum well cells, InGaAs/GaAsP middle cell optimization for 4 junction tandem cells, middle cell application of wire-on-well structures, and observation of intermediate bands in wire-on-well structures are being researched.

4. Low Cost and High Efficiency Solar Power Systems Development
Y. Nakano, J. F. Gillemores, M. Sugiyama, K. Watanabe, T. Tanemura, A. Dellamare, D. Yamashita, T. Nakata, A. Reddy, H. H. Huang, and B. Thomas

 We are studying novel high efficiency and low cost structures of solar cells utilizing epitaxial lift-off and wafer bonding technologies, highly-efficient solar power modules, and their applications to power generation systems. The subject includes the light management in ultra-high efficiency solar cells as well as cell characterization technologies. In succession from last year, we are investigating process techniques for making high efficiency solar cells into thin films, surface activation bonding, low cost light concentrating modules, and airborne solar power generation using thin film cells and balloons.

5. Heterogenious MOVPE and Optical Device Applications
Y. Nakano, M. Sugiyama, T. Tanemura, E. Kato, T. Watanabe, B. Kim, and T. Okada

We study III-V and III-nitride compound semiconductor crystal growth technologies on heterogenious materials such as silicon, sapphire, and aluminum nitride (AlN) by metal-organic vapor phase epitaxy (MOVPE), and their applications to optical devices. In previous years, we have been researching high-quality GaN/InGaN growth on silicon and monolithic white light emitting diodes using growth on AlN. This year we are focusing on InGaAs growth on silicon and its application to infrared image sensors, as well as on GaAsP growth on silicon and its application to multiple junction solar cells.

6. Photo-Electro-Chemistry and Renewable Energy Storage
Y. Nakano, M. Sugiyama, K. Fujii, M. Sato, F. Khan, H. Hashiba, Y. Imazeki, and H. Maruyama

In order to solve the problem of renewable energy being unevenly distributed in time and space, we are studying large-scale low-cost storage technologies for renewable energy. More specifically, we investigate energy storage by efficient hydrogen generation in electrochemical water splitting directly driven by the highly-efficient solar cells, as well as fuel and hydrocarbon raw material generation through direct reduction of carbon dioxide by the photovoltage. Specific research subjects are, as in the last year, III-nitride electrodes, catalysts for water splitting and carbon dioxide reduction, and high efficiency reduction chambers.

7. Sustainable Global Energy System Based on Sunlight Energy
Y. Nakano, G. Mogi, M. Sugiyama, and K. Watanabe

 Under the presidential endowed chair of "sustainable global energy system based on sunlight energy (global solar plus initiative, GS+I)", we work towards eternally sustainable global energy system that should replace current fossil fuel system by harvesting and storing the sunlight energy in large scale in low latitude desert areas where sunlight energy resource is abundant, by utilizing the energy locally for the time being, and by transporting, circulating, and utilizing it all over the world in the future. A large scale concentrator solar power generation demonstration in a desert area is being planned.