Masaomi Yamaguchi

Novel multi-bit SONOS type flash memory using a high-k charge trapping layer

We demonstrated SONOS flash memory with a SiO/sub 2//High-k/SiO/sub 2/ structure based on a 2-bit/cell scheme. We evaluated three kinds of high-k dielectric films which were Si/sub 3/N/sub 4/, Al/sub 2/O/sub 3/ and HfO/sub 2/. Among these films, Al/sub 2/O/sub 3/ showed superior retention characteristics. The charge loss amount of Al/sub 2/O/sub 3/ at 150/spl deg/C is almost the same as that of Si/sub 3/N/sub 4/ at 25/spl deg/C. HfO/sub 2/ showed poor retention characteristics. In addition, we have found that each film has a different charge loss mechanism. We speculate that Si/sub 3/N/sub 4/ causes vertical charge migration, Al/sub 2/O/sub 3/ causes scarcely any leakage, and HfO/sub 2/ causes lateral charge migration. As a consequence, Al/sub 2/O/sub 3/ is very suitable for a charge trapping layer in multi-bit SONOS memory.

Ultrafast all-optical spin polarization switch using quantum-well etalon

Ultrafast all-optical switch is proposed and demonstrated using picoseconds spin-polarization relaxation in a multiple-quantum-well (MQW) etalon structure. The decay time of the conventional all-optical switching in MQW etalon is restricted by the carrier lifetime, typically in nanoseconds. Using carrier spin relaxation, the polarization change of the probe beam has been demonstrated to be switched with a pulse width of 4 ps and a contrast of 4:1 at a pump pulse energy of 50 fJ//spl mu//sup 2/. In the present device, the contrast is determined by the polarization rotation angle of the probe beam, and the polarization-rotation angle has been shown to be proportional to the total well thickness. It is predicted that a contrast can be improved over 13 dB by optimizing the MQW etalon structure, indicating potential applicability to ultrafast optical communication systems. The optimization would improve the transmission from a present value of about 1%.

Patterned self-assembly of one-dimensional arsenic particle arrays in GaAs by controlled precipitation

A process for the patterned self‐assembly of nanometer‐scale particles within a solid is described. The process uses crystal strain and composition to guide the formation of arsenic precipitates in GaAs‐based epitaxial layers grown at low temperature by molecular beam epitaxy. The lateral particle position is controlled by the strain produced by a surface stress structure while the vertical position is controlled by the epitaxial layer composition. Arsenic particles ∼16‐nm in diameter are fabricated in one‐dimensional arrays with a 23‐nm edge‐to‐edge particle spacing at a depth of 45 nm below stressors 200 nm in width, thereby demonstrating this technique.

Extremely high temperature (220°C) continuous-wave operation of 1300-nm-range quantum-dot lasers

High temperature (>125°C) resistant semiconductor lasers are attractive as light sources in a variety of harsh environments [1]. Long-wavelength lasers operating under higher temperature of more than 200°C combined with silica-based optical fibers can expand application fields of data transmission and optical sensing to severe environments like space or deep underground. Temperature dependence of the threshold current of a semiconductor laser can be drastically reduced by employing quantum-dot (QD) active layers [2, 3]. Recent progress in epitaxial growth technology of QDs enhances the laser characteristics [3, 4]. Here, we report extremely high temperature continuous-wave (CW) operation up to 220°C of QD lasers emitted at 1300-nm-range for the first time by enhancing gain and increasing the quantized-energy separation of the QD active layers. Thus, QD lasers are proved to be suitable light sources for high temperature resistant applications.

High-speed and temperature-insensitive operation in 1.3-µm InAs/GaAs high-density quantum dot lasers

Temperature-insensitive 10.3-Gb/s operation under fixed driving condition was demonstrated using directly-modulated InAs/GaAs high-density quantum dot lasers, maintaining an Ethernet mask margin of 48 % up to 100 °C. 20-Gb/s direct modulation has also been demonstrated.

Formation of HfSiON/SiO/sub 2//Si-substrate gate stack with low leakage current for high-performance high-/spl kappa/ MISFETs

The authors found the method to form HfSiON film with an ultrathin SiO/sub 2/ interfacial layer on the Si substrate by oxidizing the HfSiN. The HfSiN film was deposited by using the metal-organic chemical vapor deposition reactor with the shower head, supplying metal (Hf and Si) precursors and NH/sub 3/ gas separately from discharge nozzles. The authors successfully decreased the leakage current of the metal insulator semiconductor diode with HfSiON/SiO/sub 2/ insulator of 1-nm equivalent oxide thickness to 0.036 A/cm/sup 2/ at V/sub fb/-1 V.

Temperature-stable 25-Gbps direct-modulation in 1.3-μm InAs/GaAs quantum dot lasers

By clarifying the temperature and mirror-loss dependence of modulation bandwidth of 1.3-μm-wavelength InAs/GaAs quantum-dot lasers, temperature-stable 25-Gbps direct-modulation is achieved from 20 to 70°C with fixed bias and modulation currents.

Long-wavelength quantum dot FP and DFB lasers for high temperature applications

High temperature (>125°C) resistant long-wavelength semiconductor lasers are attractive as light sources in a variety of harsh environments. Here, we report extremely high temperature continuous-wave (CW) operation of QD lasers on GaAs substrate emitted at 1300-nm-range by enhancing gain and increasing the quantized-energy separation of the QD active layers. A suppression of the In out-diffusion during MBE from self-assembled InAs QDs significantly reduced inhomogeneous broadening with high QD sheet density maintained. QD-FP laser exhibited record high CW-lasing temperature for long-wavelength laser of 220°C and QD-DFB laser also exhibited high CW-lasing temperature of 150°C by employing high gain QD active media.

Effect of carrier transport on modulation bandwidth of 1.3-µm InAs/GaAs self-assembled quantum-dot lasers

We newly modeled the modulation bandwidth of 1.3-µm quantum-dot lasers and analyzed experimental results. The carrier transport through the active layers was found to affect significantly the modulation bandwidth with increasing stacking-number of quantum-dot layers.

Effect of in-situ nitrogen doping into MOCVD-grown Al/sub 2/O/sub 3/ to improve electrical characteristics of MOSFETs with polysilicon gate

The effect of nitrogen doping into Al/sub 2/O/sub 3/ gate dielectric grown by Metal Organic Chemical Vapor Deposition (MOCVD) on MOS device characteristics is described for the first time. The nitrogen doped Al/sub 2/O/sub 3/ (Al/sub 2/O/sub 3/:N) MOSFET has an interface trap density (D/sub it/) as low as 4.3/spl times/10/sup 10/ cm/sup -2/ eV/sup -1/, half that of non-doped Al/sub 2/O/sub 3/ (1.0/spl times/10/sup 11/ cm/sup -2/ eV/sup -1/), and has less C-V hysteresis (39 mV) than that (69 mV) of Al/sub 2/O/sub 3/. These improvements are attributed to nitrogen doping into Al/sub 2/O/sub 3/, which also improves the corresponding MOSFET characteristics of current drivability (I/sub dsat/).