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Physics and application of single quantum dot transistors

Self-assembled semiconductor quantum dots (QDs) are often called “artificial atoms” and manifest novel physics that originate from quantized electron orbitals and spins. In 2005, we discovered a remarkable feature that, when a single InAs QD is touched by 2 metal electrodes with a nanogap, it behaves as a single electron transistor (SET) (M. Jung, K. Hirakawa, et al., Appl. Phys. Lett., 86, 033106 (2005)). We are working on novel physics and device applications of such semiconductor quantum dot/metal electrode junctions. Particularly, we are making efforts on terahertz dynamics ... Read more

• Terahertz intersublevel transition spectroscopy of single InAs quantum dots
• Control of electronic states in quantum dots by using ionic liquid gating
• Terahertz photon-assisted tunneling in quantum dots
• Site- and shape-controlled growth of InAs quantum dots
• Probing manybody quantum states in single InAs quantum dots: terahertz and tunneling spectroscopy
• Obervation of single-electron terahertz photovoltaic effect in quantum dots

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Atomic-scale nanofabrication and single molecule transistors

Molecules are the smallest structures that can perform functions. We are working on atomic-scale nanofabrication technologies to make contact to single molecules. In particular, we have clarified the elementary process of a phenomenon called “electromigration”, which is used to fabricate nanogap electrodes by the electrical break junction method, and improved the fabrication yield of single molecule transistors dramatically. Furthermore, we are exploring new paradigm for electronics that utilize novel functions of single molecule devices. Topics Physics of electromigration in... Read more

• Physics of electromigration in atomic-scale metal nanocontacts
• Electron transport in single C60 molecule transistors with ferromagnetic Ni electrodes
• Nanomechanical rotation of molecules in single H2TPP molecule transistors

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Electronic properties and device application of quantum nanostructures in the THz range

Semiconductor superlattice, proposed in 1970 by Esaki and Tsu, is a one-dimensional man-made periodic structure, which usually consists of a stack of two different semiconducting materials. It is known that a system with a periodic potential has a remarkable feature that electrons perform oscillatory motion when accelerated by dc electric fields (Bloch oscillation). Bloch oscillator is a device concept that utilizes such an oscillatory electron motion for realizing ultra-high frequency oscillators. We work on the dynamics of Bloch oscillating electron in semiconductor superlattices by using... Read more

• Bloch oscillation and THz gain in semiconductor superlattices
• Analysis of carrier dynamics in THz quantum cascade lasers by using non-equilibrium Green’s function approach

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Generation/detection of THz/infrared radiations and its application to spectroscopy

Recent progress in femtosecond laser technologies has developed various kinds of THz technologies. We have been working on novel ultrafast spectroscopy technique called time-domain THz spectroscopy, which serves as an “oscilloscope” in the THz frequency range. Another important subject is the development of THz detectors. We are investigating various schemes for sensitive THz detection. Furthermore, we work on THz/infrared spectroscopy of proteins for applications in food science. Topics High-sensitivity THz detection using MEMS Novel THz detection devices using quantum nanostructures Dr... Read more

• High-sensitivity THz detection using MEMS

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