Yoko Sakurai

Temperature Dependence of Electron Tunneling between Two Dimensional Electron Gas and Si Quantum Dots

Quantum mechanical electron tunneling has potential applications in both science and technology, such as flash memories in modern LSI technologies and electron transport chains in biosystems. Although it is known that one-dimensional quantum electron tunneling lacks temperature dependence, the behavior of electron tunneling between different dimensional systems is still an open question. Here, we investigated the electron tunneling between a two-dimensional electron gas (2DEG) and zero-dimensional Si quantum dots and discovered an unexpected temperature dependence: At high temperature, the gate voltage necessary for electron injection from 2DEG to Si quantum dots becomes markedly small. This unusual tunneling behavior was phenomenologically explained by considering the geometrical matching of wave functions between different dimensional systems. We assumed that electron tunneling would occur within a finite experimental measurement time. Then, the observed electron tunneling is explained only by the contributions of wave packets below the quantum dot with a finite lifetime rather than the ordinary thermal excited states of 2DEG.

Collective Tunneling Model between Two‐Dimensional Electron Gas to Si‐Nano Dot

We study the temperature dependence of electron injection voltage in Si‐Nano‐Dot (Si‐NDs) Floating Gate MOS capacitor by using the collective tunneling model, which models the tunneling between two‐dimensional electron gas (2DEG) and the Si‐NDs. We clarify the temperature dependence by numerical calculation, which emulate the experiment in this system, and we obtained a new insight into the origin of the temperature dependence. We have revealed that the collective tunneling model can reproduce the temperature dependence of electron tunneling.

Collective Tunneling Model in Charge-Trap-Type Nonvolatile Memory Cell

A new tunneling model between an inversion layer and the trap sites for the charge-trap-type (CT-) nonvolatile memory (NVM) cell is proposed. By considering the geometrical mismatch between the inversion layer and the trap site of the CT-NVM cell, we can conclude that electron tunneling is induced by a rare event, which causes the localization of electrons in the inversion layer near the trap sites. In addition, we also reveal that the successive tunneling of electrons is triggered by this rare event tunneling by focusing on the temporal fluctuation of the electronic state in the inversion layer. On the basis of these phenomena, we propose the collective tunneling model in the charge injection of the CT-NVM cell, where the electrons tunnel to the trap sites collectively with a long waiting time. This insight is important in designing the CT-NVM cell. By using collective tunneling, the amount of injection charge can be controlled discretely by adjusting the charge injection time. This enables us to realize a multilevel charge trap cell.

Photoluminescence characterization in silicon nanowire fabricated by thermal oxidation of nano-scale Si fin structure

Low-temperature photoluminescence (PL) spectra of electron-hole systems in Si nanowires (NWs) prepared by thermal oxidization of Si fin structures were studied. Mapping of PL reveals that NWs with uniform width are formed over a large area. Annealing temperature dependence of PL peak intensities was maximized at 400 °C for each NW type, which are consistent with previous reports. Our results confirmed that the micro-PL demonstrated here is one of the important methods for characterizations of the interface defects in Si NWs.

Fast luminescence decay of electron-hole quasi-two dimensional systems in Si nanolayer

We have studied the photoluminescence (PL) spectra and PL decay profiles of electron-hole systems in high quality Si nanolayers. We have found that the PL lifetime decreases with decrease in the thickness of silicon nanolayers between 25.2 and 2.7 nm and with decrease in temperature between 5 and 70 K.

Collective Electron Tunneling Model in Si-Nano Dot Floating Gate MOS Structure

We study the sweep speed dependence of electron injection voltage in Si-Nano-Dots (Si-NDs) floating gate MOS Capacitor by using our collective tunneling model, which models the tunneling between two-dimensional electron gas (2DEG) and the Si-NDs. We clarify the sweep speed dependence of electron injection energy with a numerical calculation based on our collective tunneling model, that we developed to emulate the experiment in this system, and obtained a new insight into the origin of sweep speed dependence. We revealed that our model can reproduce the sweep speed dependence of electron tunneling. This insight is useful for designing future nano-electronic devices.

Photoluminescence Characteristics of Ultra-Thin Silicon-on-Insulator at Low Temperatures

We have investigated C-V and photoluminescence (PL) characteristics of ultra-thin silicon-on-insulator (SOI) samples. Thickness dependence of a free exciton (FE) PL and an electron-hole droplet (EHD) PL has been investigated. We have found a remarkable enhancement of an EHD PL with decrease in the thickness of SOI samples.

Collective Tunneling Model in Charge Trap Type NVM Cell

Masakazu Muraguchi, Yoko Sakurai, Yukihiro Takada, Yasuteru Shigeta, Mitsuhisa Ikeda, Katsunori Makihara, Seiichi Miyazaki, Shintaro Nomura, Kenji Shiraishi, and Tetsuo Endoh Center for Interdisciplinary Research, Tohoku University, 6-3 Aramaki aza Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan Graduate School of Pure and Applied Science, University of Tsukuba 1-1-1 Tennodai, Tsukuba, Ibaraki, Japan Graduate School of Advanced Sciences of Matter, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8530, Japan Graduate School of Life Science, University of Hyogo, 3-2-1 Kouto, Kamigoori, Ako-Gun, Hyogo 678-1297, Japan

New Tunneling Model with Dependency of Temperature Measured in Si Nano-Dot Floating Gate MOS Capacitor

Measured in Si Nano-Dot Floating Gate MOS Capacitor Masakazu Muraguchi, Yoko Sakurai, Yukihiro Takada, Yasuteru Shigeta, Mitsuhisa Ikeda, Katsunori Makihara, Seiichi Miyazaki, Shintaro Nomura, Kenji Shiraishi, and Tetsuo Endoh Center for Interdisciplinary Research, Tohoku University, Sendai, Japan Phone +81 22-795-5260 E-mail: muraguchi@cir.tohoku.ac.jp 2 Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba, Japan 3 Graduate School of Advanced Sciences of Matter, Hiroshima University, Hiroshima, Japan 4 Graduate School of Life Science, University of Hyogo, Hyogo, Japan