S. Adachi
Hokkaido University
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Publication
Featured researches published by S. Adachi.
IEEE Journal of Solid-state Circuits | 2006
Nana Akahane; Shigetoshi Sugawa; S. Adachi; Kazuya Mori; Toshiyuki Ishiuchi; Koichi Mizobuchi
In a CMOS image sensor featuring a lateral overflow integration capacitor in a pixel, which integrates the overflowed charges from a fully depleted photodiode during the same exposure, the sensitivity in nonsaturated signal and the linearity in saturated overflow signal have been improved by introducing a new pixel circuit and its operation. The floating diffusion capacitance of the CMOS image sensor is as small as that of a four transistors type CMOS image sensor because the lateral overflow integration capacitor is located next to the reset switch. A 1/3-inch VGA format (640/sup H//spl times/480/sup V/ pixels), 7.5/spl times/7.5 /spl mu/m/sup 2/ pixel color CMOS image sensor fabricated through 0.35-/spl mu/m two-poly three-metal CMOS process results in a 100 dB dynamic range characteristic, with improved sensitivity and linearity.
international solid-state circuits conference | 2006
Nana Akahane; R. Ryuzaki; S. Adachi; Koichi Mizobuchi; Shigetoshi Sugawa
A 2.6times2.6mm<sup>2</sup> image sensor fabricated in 0.35mum 2P3M CMOS contains 64times64 pixels with 20times20mum<sup>2</sup> pixel size and has an extended dynamic range of over 200dB. This DR is equivalent to the incident light ranging from about 10<sup>-2</sup> to 10<sup>8</sup> lx with the lens iris fixed
Applied Physics Letters | 2011
S. Ohno; S. Adachi; R. Kaji; Shunichi Muto; Hirotaka Sasakura
We have investigated the optical anisotropy in individual self-assembled quantum dots. The linear polarization analysis of the positive trion photoluminescence reveals the effect of the strain-induced valence band mixing since the positive trion has the spin-paired holes and therefore exchange interaction has no influence. Meanwhile, the neutral exciton indicates the complex polarization states due to both the in-plain asymmetries of the dot shape and the strain distributions. The experimental and theoretical polarization analysis has been performed for tens of InAlAs quantum dots and the correlation between the important parameters was investigated.
Applied Physics Letters | 2007
T. Ishiguro; Yasunori Toda; S. Adachi
The authors studied the exciton spin relaxation of bulk GaN by creating spin polarization gratings using degenerate four-wave mixing spectroscopy. The spectrally resolved analysis achieved with this technique facilitated the direct evaluation of spin polarizations in the individual excitons (A and B excitons). The spin polarizations for each exciton decay very quickly (τs∼1ps) at low temperatures. Moreover the τs is faster than the dephasing time T2 throughout the measured temperature range, suggesting the existence of fast intrinsic spin relaxation processes, which can be attributed to a large exchange constant characterized in GaN.
Optics Communications | 2000
S. Adachi; Yoshihiro Takagi; Jun Takeda; Keith A. Nelson
We have developed the optical sampling four-wave mixing technique applicable to measurements of the ultrafast dynamical processes in liquid and solid materials. The method is examined to reveal the exciton dynamical processes in GaAs quantum wells at low temperatures. By using the optical sampling principle, this new spectroscopic tool provides well timing-controlled two-color light pulses for excitation and detection, and also wide observable temporal range from sub-picoseconds to a few nanoseconds with femtosecond time resolution. Various transient processes such as phase relaxation, spin relaxation, and energy relaxation processes can therefore be observed rapidly in the common measurement system.
Review of Scientific Instruments | 1999
Yoshihiro Takagi; S. Adachi
We have developed a subpicosecond nondegenerate pump-probe spectrometer based on the optical sampling technique using a combination of asynchronous tunable femtosecond lasers. Owing to its simple instrumentation, time evolution of subpicosecond to nanosecond excited molecular processes in solution and of exciton relaxation processes in semiconductor multiple quantum wells has been detected on an oscilloscope by an effective time base magnification of 760 000 times. Fast acquisition of the temporal profiles and ease of wavelength scanning allowed compilation of time-resolved absorption and excitation spectra. A possible extention of the spectrometer with one of the light sources being a synchrotron radiation instead of the femtosecond laser is discussed.
Physical Review B | 2005
T. Yokoi; S. Adachi; Hirotaka Sasakura; Shunichi Muto; H. Z. Song; Tatsuya Usuki; S. Hirose
We report optical spectroscopic results of a single self-assembled
Applied Physics Letters | 2005
Shunichi Muto; S. Adachi; T. Yokoi; Hirotaka Sasakura; Ikuo Suemune
{\mathrm{In}}_{0.75}{\mathrm{Al}}_{0.25}\mathrm{As}∕{\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}
Optics Communications | 1995
S. Adachi; Shojiro Takeyama; Yoshihiro Takagi
quantum dot. The polarization-dependent shift of the Zeeman splitting in a single InAlAs quantum dot (QD) has been observed. The induced Overhauser field is estimated to be
Japanese Journal of Applied Physics | 2004
Hirotaka Sasakura; S. Adachi; Shunichi Muto; Hai Zhi Song; Toshiyuki Miyazawa; Tatsuya Usuki
\ensuremath{\sim}0.16\phantom{\rule{0.3em}{0ex}}\mathrm{T}