S. Adachi

A sensitivity and linearity improvement of a 100-dB dynamic range CMOS image sensor using a lateral overflow integration capacitor

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.

A 200dB Dynamic Range Iris-less CMOS Image Sensor with Lateral Overflow Integration Capacitor using Hybrid Voltage and Current Readout Operation

A 2.6times2.6mm² image sensor fabricated in 0.35mum 2P3M CMOS contains 64times64 pixels with 20times20mum² pixel size and has an extended dynamic range of over 200dB. This DR is equivalent to the incident light ranging from about 10^-2 to 10⁸ lx with the lens iris fixed

Optical anisotropy and photoluminescence polarization in single InAlAs quantum dots

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.

Exciton spin relaxation in GaN observed by spin grating experiment

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.

Optical sampling four-wave-mixing experiment for exciton relaxation processes

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.

SUBPICOSECOND OPTICAL SAMPLING SPECTROMETER USING ASYNCHRONOUS TUNABLE MODE-LOCKED LASERS

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.

Polarization-dependent shift in excitonic Zeeman splitting of self-assembled In0.75Al0.25As /Al0.3Ga0.7As quantum dots

We report optical spectroscopic results of a single self-assembled

Photon-spin qubit-conversion based on Overhauser shift of Zeeman energies in quantum dots

{\mathrm{In}}_{0.75}{\mathrm{Al}}_{0.25}\mathrm{As}∕{\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}

Dual wavelength optical sampling technique for ultrafast transient bleaching spectroscopy

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

Spin Depolarization via Tunneling Effects in Asymmetric Double Quantum Dot Structure

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