Faculty Profiles - OHNO, Yutaka

Photoluminescence of single-walled carbon nanotubes in field-effect transistors

AlGaN/GaN high electron mobility transistors with inclined-gate-recess structure

Aoi Yuma, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 45 ( 4B ) page： 3368 - 3371 2006.4

Ohno Y, Kishimoto S, Mizutani T

NANOTECHNOLOGY Vol. 17 ( 2 ) page： 549 - 555 2006.1

Language：Japanese Publisher：Nanotechnology

We have studied the photoluminescence (PL) of individual single-walled carbon nanotubes (SWNTs) placed in field-effect transistor structures. The SWNTs were suspended in the air so that strong PL was obtained. When an external bias voltage was applied to the device, no spectral changes could be detected, but the intensity drastically increased or decreased. This behaviour is explained by the injection/extraction of carriers from/to the electrodes by the electric field. In the case of p-type FETs in the air, PL intensity increased due to hole injection by applying a small negative gate bias. After the device was heated in vacuum, the maximum PL intensity was obtained at zero gate bias. This can be explained by the change in the interface between the SWNT and contact electrodes. The drain field dependence of the PL intensity shows a monotonic decrease, which is explained by a competition between the recombination lifetime and transit time of photo-excited carriers in the SWNT. Using analytical steady-state rate equations on carrier density in the SWNT, the relation between the recombination lifetime and carrier transit time has been evaluated. The carrier saturation velocity has also been estimated. © 2006 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/17/2/035

AlGaN/GaN MIS-HEMTs with ZrO<inf>2</inf> gate insulator

(解説)カーボンナノチューブのフォトルミネッセンス

大野雄高

ナノ学会会報 4 page： 67 2006

27aUA-1 Chirality-dependent environmental effect on photoluminescence in carbon nanotubes Open Access

Ohno Y., Iwasaki S., Murakami Y., Kishimoto S., Maruyama S., Mizutani T.

Meeting Abstracts of the Physical Society of Japan Vol. 61.1.4 ( 0 ) page： 805 2006

Sugimoto T., Ohno Y., Kishimoto S., Maezawa K., Osaka J., Mizutani T.

Institute of Physics Conference Series Vol. 184 page： 279 - 282 2005.12

Language：Japanese Publisher：Institute of Physics Conference Series

AlGaN/GaN MIS-HEMTs using ZrO2 gate insulator with a large dielectric constant have been successfully fabricated. The gate leakage current decreased by more than three orders of magnitude compared to that of the conventional AlGaN/GaN HEMTs without the ZrO2 gate insulator. Current collapse has also been suppressed in the MIS-HEMTs. The decrease in g mmax, which was observed in the case of Si3N4 MIS-HEMTs, was suppressed in the present MIS-HEMTs demonstrating the effectiveness of the ZrO2 gate insulator. © 2005 IOP Publishing Ltd.

Electron traps in AlGaN/GaN MIS-HEMTs observed by drain current DLTS

Okino T., Ohno Y., Kishimoto S., Maezawa K., Osaka J., Mizutani T.

Institute of Physics Conference Series Vol. 184 page： 271 - 274 2005.12

Surface potential transient of AlGaN/GaN HEMTs measured by Kelvin probe force microscopy

Nakagami K., Ohno Y., Kishimoto S., Maezawa K., Mizutani T.

Institute of Physics Conference Series Vol. 184 page： 275 - 278 2005.12

Language：Japanese Publisher：Institute of Physics Conference Series

Surface potential of the AlGaN/GaN high-electron-mobility transistors was measured by Kelvin probe force microscopy to study the mechanism of the drain current collapse. The potential after the gate bias stress increased due to the emission of trapped electrons from the surface states. The time constant of the potential increase was 75 s, which was comparable to that of the drain current recovery from the collapsed level. © 2005 IOP Publishing Ltd.

Deep levels in n-type AlGaN grown by hydride vapor-phase epitaxy on sapphire characterized by deep-level transient spectroscopy

Osaka J, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

APPLIED PHYSICS LETTERS Vol. 87 ( 22 ) page： 1 - 3 2005.11

Language：Japanese Publisher：Applied Physics Letters

Deep levels in unintentionally doped n -type Al0.09 Ga0.91 N and Al0.17 Ga0.83 N films grown on sapphire by hydride vapor-phase epitaxy were characterized using capacitance deep-level transient spectroscopy and were compared to the reported electron traps in GaN grown by various techniques. It was shown that at least three dominant deep levels exist in each sample. The Al mole fraction dependence of their activation energy suggested that each of these three levels has the same origin as the three dominant well known point-defect-related deep levels in GaN, respectively. It is thought that deep levels in GaN change their electric characteristics in low Al content AlGaN. © 2005 American Institute of Physics.

DOI： 10.1063/1.2137901

Direct integration of GaAsHEMTs on AlN ceramic substrates using fluidic self-assembly

Soga I, Hayashi S, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

ELECTRONICS LETTERS Vol. 41 ( 23 ) page： 1275 - 1276 2005.11

Language：Japanese Publisher：Electronics Letters

Direct integration of AlGaAs/GaAs HEMTs on AlN ceramic substrates has been demonstrated based on the fluidic self-assembly (FSA) technology. The FSA is a unique technology to arrange small device blocks (around a few tens of microns) onto the other substrates. With this technology the core part of the HEMT having no pad can be mounted on the ceramic substrate. The HEMT core can then be connected electrically with the circuit on a ceramic substrate using a planar wiring process. This eliminates large stray capacitance and inductance in the conventional technology. It has been demonstrated that the good FET characteristics are obtained even after FSA process. © IEE 2005.

DOI： 10.1049/el:20052840

Metamorphic Resonant Tunneling Diodes and Its Application to Chaos Generator ICs

Maezawa Koichi, Iwase Takashi, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi, Sano Kimikazu, Takakusaki Misao, Nakata Hirofumi

Japanese Journal of Applied Physics Vol. 44 ( 7A ) page： 4790 - 4794 2005.7

Language：Japanese Publisher：The Japan Society of Applied Physics

In this paper we discuss the properties of InGaAs/AlAs metamorphic resonant tunneling diodes (RTDs) on GaAs substrates. The current–voltage, surface roughness, and low-frequency noise characteristics were investigated to clarify the effect of step-grading buffer layers. No degradation of the current–voltage characteristics were observed despite the large surface roughness due to a lattice mismatch. Moreover, low-frequency noise measurements showed only 1⁄f noise without special peak structures, and the amplitudes of which were comparable to those of the lattice-matched ones. Next, we fabricated resonant tunneling frequency divider ICs, which is based on the bifurcation phenomenon in a chaos system, on metamorphic substrates. A maximum operation frequency of 88 GHz and good phase noise properties were obtained, which are similar to those of the lattice-matched ones. These results demonstrate the effectiveness of the step-grading buffer layers even for the RTDs that consist of very thin layers and are sensitive to crystal qualities.

DOI： 10.1143/JJAP.44.4790

Effects of Fabrication Process on Current-Voltage Characteristics of Carbon Nanotube Field Effect Transistors

Mizutani Takashi, Iwatsuki Shinya, Ohno Yutaka, Kishimoto Shigeru

Japanese Journal of Applied Physics Vol. 44 ( 4A ) page： 1599 - 1602 2005.4

Language：Japanese Publisher：The Japan Society of Applied Physics

The effects of the fabrication process on the current–voltage (I–V) characteristics of carbon nanotube field effect transistors (CNT-FETs) were studied in detail. A large hysteresis observed in the I–V characteristics of the CNT-FETs having no passivation film became small by passivating the device surface with a SiNx film. The conduction behaivior of the CNT-FETs changed from p-type to ambipolar characteristics by SiNx passivation. Ambipolar characteristics were also observed in the top-gate CNT-FETs with a gate-source spacing of 2 μm.

DOI： 10.1143/JJAP.44.1599

Growth of mm-Long Carbon Nanotubes by Grid-Inserted Plasma-Enhanced Chemical Vapor Deposition Open Access

Kishimoto Shigeru, Kojima Yoshihiro, Ohno Yutaka, Sugai Toshiki, Shinohara Hisanori, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 44 ( 4A ) page： 1554 - 1557 2005.4

Language：Japanese Publisher：The Japan Society of Applied Physics

Vertically aligned long multi-walled carbon nanotubes (MWNTs) have been successfully grown by grid-inserted plasma-enhanced chemical vapor deposition (PECVD). A thin Fe (1 nm)/Ti (1 nm) double-layer catalyst was effective in growing the long MWNTs. The length of the MWNTs increased to 1 mm for the growth time of 120 min without growth termination. A thick Fe catalyst or thick Ti underlayer resulted in a low growth rate. Transmission electron microscopy, energy-dispersive X-ray analysis and thermo-gravimetric analysis (TGA) measurements suggest that the MWNTs were grown in a root growth mode. Moreover, the TGA measurements suggest that MWNTs of high quality/purity were successfully grown by grid-inserted PECVD with a double-layer catalyst.

DOI： 10.1143/JJAP.44.1554

Growth of High-Quality Carbon Nanotubes by Grid-Inserted Plasma-Enhanced Chemical Vapor Deposition for Field Emitters

Kojima Yoshihiro, Kishimoto Shigeru, Ohno Yutaka, Sakai Akira, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 44 ( 4B ) page： 2600 - 2603 2005.4

Language：Japanese Publisher：The Japan Society of Applied Physics

The effect of a grid inserted between the anode and the cathode in plasma-enhanced chemical vapor deposition (PECVD) on carbon nanotube (CNT) growth was studied. The optimum grid-cathode distance and grid-cathode voltage were 4 mm and 2–10 V, respectively. Long small-diameter nanotubes were grown under these conditions. The smallest nanotube diameter obtained was 3 nm. However, when the grid-cathode voltage was higher than 10 V, short large-diameter nanotubes were grown. The field emission characteristics of CNTs with a low ON voltage and a high current density were explained by Fowler-Nordheim (FN) tunneling.

DOI： 10.1143/JJAP.44.2600

Photoresponse of Carbon Nanotube Field-Effect Transistors

Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 44 ( 4A ) page： 1592 - 1595 2005.4

Language：Japanese Publisher：The Japan Society of Applied Physics

Photoresponse of carbon nanotube field-effect transistors (FETs) is investigated using microscopic measurements. The nanotube FETs, with an isolated single-walled carbon nanotube (SWNT) for the channel, were fabricated by means of the position-controlled nanotube growth technique. An increase in the off-state current and the threshold-voltage shift of the FET were caused by laser illumination. The increase in the off-state current is attributed to photocurrent due to carriers excited in the SWNT channel. The excitation spectrum of the photocurrent had a peak corresponding to optical absorption by the third interband gap of the van Hove singularity of the semiconducting SWNT with a diameter of ∼2 nm. The photocurrent increased in proportion to incident laser power with a dynamic range over four orders of magnitude. The external quantum efficiency was 2×10−7. An inverter action to optical-signal input was observed near the threshold voltage of the FET. The responsivity was as high as 2×10−3 A/W for a single SWNT channel. This high responsivity is explained by the field-effect amplification phenomenon.

DOI： 10.1143/JJAP.44.1592

n-Type carbon nanotube field-effect transistors fabricated by using Ca contact electrodes Open Access

Nosho Y, Ohno Y, Kishimoto S, Mizutani T

APPLIED PHYSICS LETTERS Vol. 86 ( 7 ) 2005.2

Synthesis of carbon nanotube peapods directly on Si substrates Open Access

Ohno Y, Kurokawa Y, Kishimoto S, Mizutani T, Shimada T, Ishida M, Okazaki T, Shinohara H, Murakami Y, Maruyama S, Sakai A, Hiraga K

APPLIED PHYSICS LETTERS Vol. 86 ( 2 ) 2005.1

Tunable Field-Effect Transistor Device with Metallofullerene Nanopeapods

Shimada Takashi, Ohno Yutaka, Suenaga Kazutomo, Okazaki Toshiya, Kishimoto Shigeru, Mizutani Takashi, Taniguchi Risa, Kato Haruhito, Cao Baopeng, Sugai Toshiki, Shinohara Hisanori

Japanese Journal of Applied Physics Vol. 44 ( 1A ) page： 469 - 472 2005.1

Language：Japanese Publisher：The Japan Society of Applied Physics

A fine tuning of the band gap of single-wall carbon nanotubes (SWNTs) has been achieved by filling various types of endohedral metallofullerenes into the SWNTs, the so-called nanopeapods. We report various electronic transport properties of fullerene peapods used as the channels of field-effect transistors (FETs) and demonstrate that the metallofullerene peapods can provide the tunable band gaps of the FET channels depending on the type of metallofullerene inserted in the SWNTs. All of the metallofullerene peapods FETs exhibit p- and n-type, the so-called ambipolar carrier transportation by variable gate bias. The ranges of the off state regions of the FET fabricated highly sensitivity with respect to the amount of charge transfer in metallofullerenes, which results in band-gap engineering. Metallofullerene peapods can be used to manipulate the electronic structure of SWNTs in nanometer scale. In such a highly functionalized SWNT, metallofullerene peapods, might be a key material for fabricating and developing sophisticated electronic devices in the future.

DOI： 10.1143/JJAP.44.469