A02 group

A02-1 Development of diamond electron device using III-nitride nanolaminate singularity structure

  • Principal Investigator / Yasuo Koide (National Institute for Materials Science / Executive Vice President)
  • Co-Investigator / Masataka Imura (National Institute for Materials Science / Senior Researcher)
  • Co-Investigator / Meiyong Liao (National Institute for Materials Science / Senior Researcher)
  • Co-Investigator / Jiangwei Liu (National Institute for Materials Science / Independent Researcher)

Recently, a nanoscale multilayer material using Al2O3/TiO2, named by nanolaminate layer, has been reported to provide a high dielectric constant (k) larger than 1000 due to dielectric relaxation by Maxwell-Wagner effect. The purpose of this research is twofold. The first is to develop a singularity structure of the nanolaminate layer composed of dielectric i-AlN and conductive c-GaN with k larger than 100 and the respective 1 nm thickness. The second is to demonstrate a new-concept diamond transistor using this nanolaminate layer gate on hydrogenated (H) diamond surface. The hole carrier density in the H-terminated diamond surface is reported by our research group to be as large as 1014 cm-3 which is one-order of magnitude larger than that of commercialized AlGaN/GaN heterojuntion transistor. In order to control such the high-density hole carrier, it is required to develop the gate insulator with k larger than 100. The development of the AlN/GaN nanolaminate singularity structure is a key to success.

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A02-2 Research on novel light emitting devices by using the properties of singularity structure crystals

  • Principal Investigator / Hideki Hirayama (RIKEN / Chief Scientist)
  • Co-Investigator / Wataru Terashima (RIKEN / Researcher)
  • Co-Investigator / Norihiko Kamata (Saitama University / Professor)

In this work, we explore novel light emitting devices by introducing and using the properties of singularity structure crystals. In order to realize unexplored deep-ultraviolet (DUV) and terahertz (THz) light emitting devices, it is necessary to achieve a high hole concentration p-type AlGaN, a low dislocation density AlN buffer layer as well as AlGaN multi-stacking superlattices (SLs) with atomically flat hetero-interfaces. In this project, we will realize more than 50 % efficiency DUV light-emitting diodes (LEDs) and laser diodes (LDs) by developing pillar AlN array light extraction structure by using a self-assembling growth method and/or by developing high hole concentration p-AlGaN layers with co-doping in short-period superlattices (SPSLs). In order to achieve quantum-cascade lasers (QCLs), we need AlGaN/GaN multi-stacking SL structures with atomically flat hetero-interfaces. We will realize unexplored frequency THz-QCLs by developing high optical gain multi-stacking AlGaN/GaN high-quality SLs by using our original droplet elimination by thermal annealing (DEAT) growth method.

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A02-3 Characterization and control of GaN heterointerfaces including singularity structures for advanced electron devices

  • Principal Investigator / Tamotsu Hashizume (Hokkaido University / Professor)
  • Co-Investigator / Masamichi Akazawa (Hokkaido University / Associate Professor)
  • Co-Investigator / Taketomo Sato (Hokkaido University / Associate Professor)

GaN-based heterosystems utilizing various kinds of singularity structures and potential barriers will be high-level heterointerface continuum applicable to next-generation optical and electron devices. On the other hand, such hterointerfaces generally include high-density electronic states causing deterioration of device performances. To apply heterosystems utilizing singularity structures to high-performance devices, it is inevitable to characterize and control of interface electronic states in the vicinity of singularity structures.
In this project, we will precisely characterize electronic states of GaN-based heterosystems including singularity structures by a rigorous simulation of capacitance-voltage characteristics, transient capacitance methods and admittance analyses. From comparative studies between structural/chemical properties and electronic states, in addition, control schemes and/or processes for electronic states will be achieved.
For development of a novel electron device, we will fabricate a multi nanostructure having sidewall channels on a non-polar or a semi-polar GaN surface, as shown in the figure. In addition, we will develop novel sensor devices and ultralow resistance electrodes on the basis of nano-porous GaN structures prepared by an electrochemical process.


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A02-17-1 Fabrication and Characterization of Vertical FETs using GaN-based Nanowires

  • Principal Investigator / Junichi Motohisa (Hokkaido University / Professor)

Field effect transistors (FETs) with multi-gate structures are used in electronics, which are immune to short channel effect. Superior characteristics in current drivability, temperature stability, and bias-independent characteristics of transconductance and/or transition frequencies have are also been reported in GaN-based multi-gate FETs in the lateral geometry. In this research, we focus on novel multi-gate FETs, namely, vertical FETs having gate-all-around geometry by using selectively-grown GaN nanowires. Vertical nanowire FETs have already been realized in our group using conventional III-V semiconductor nanowires grown by selective-area growth, but no attempts have been made with GaN-based nanowires. For this purpose, we are going to investigate and explore (1) crystal growth technology to realize GaN nanowires by selective-area growth, (2) device processing technology to realize vertical FETs, and (3) nanowire-based heterostructures which are effective to improve the performance of FETs, such as GaN/AlGaN core-shell heterostructures or vertical heterostructures with InN insertion in the GaN channel.

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A02-17-2 Improvement of electrical properties of nitride semiconductors by polarization-induced effects

  • Principal Investigator / Tomoyuki Tanikawa (Tohoku University / Lecturer)

Novel semiconductor materials, such as nitride semiconductors and oxide semiconductors, have large polarization, which often affects the conduction properties of the devices. In order to improve the electrical properties of the polar-semiconductor-based devices, in this study, a polarization-induced@layer is introduced in the nitride-semiconductor-devices. By comparing the direction of polarization by changing the crystallographic polarity, the influences of polarization effects on the electrical properties will be experimentally investigated. Sample fabrication will be carried out by metalorganic vapor phase epitaxy. First, Ga-polar and N-polar GaN films are grown on sapphire substrates. Then device structures including a polarization-induced layer will be grown on them. Polarization-induced Zener tunnel diodes and polarization-doped p-type layers will be studied. For example, a thin polarization-induced AlN layer will be fabricated between p-type and n-type GaN layers, and improvement of tunnel probability will be demonstrated for Zener tunnel diodes. In addition, the enhancement of acceptor activation will be demonstrated by fabricating an alloy-composition-graded AlGaN layer as a polarization-induced layer.

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A02-17-3 Precise control of ion implantations in GaN and its application to integrated circuit

  • Principal Investigator / Hiroto Sekiguchi (Toyohashi University of Technology / Associate Professor)

We try to realize an integrated circuit based on GaN metal oxide semiconductor field effect transistor (MOSFET) for harsh environment. In this study, for development of precise control of ion implantation process, the effects of ion implantation in GaN on crystalline structure, crystal defect and impurity are clarified by evaluating structural, optical and electrical properties such as transmission electron microscope (TEM), photoluminescence (PL), cathodoluminescence (CL), and Hall effect measurement. Based on these results, the fundamental technology using ion implantation methods for the reductions of the contact resistances of source/drain, the threshold voltage control of MOSFET and the formation of insulated layer for element isolation will be developed.

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A02-17-4 Physical properties of multilayer graphene emerging from singularity in turbostratic structures

  • Principal Investigator / Yoshihiro Kobayashi (Osaka University / Professor)

Graphene has unique and practically useful physical properties, which are evident only for monolayer graphene and should be degraded for multilayer graphene due to strong interaction between graphitic layers. In this research, we will investigate multilayer graphene with singularity structure of turbostratic stacking. Turbostratic structure disturbs crystallographic periodicity for stacking direction and is commonly regarded as "defect" in graphite crystal with regular Bernal stacking. We utilize the turbostratic structure to reduce the interaction between the layers, resulting in emergence of quasi monolayer properties from multilayer graphene. We will develop a novel thermal process to synthesize multilayer turbostratic graphene, where defective graphene oxide film is heated at ultrahigh temperature around 1800C under reactive environment including alcohol. Defects in graphene oxide induced during chemical exfoliation of graphite should be repaired simultaneously by the thermal process. We expect the turbostratic structure dramatically improve electrical/thermal properties of multilayer graphene. Scalable production of high-performance graphene developed by this study will stimulate practical application of graphene to various fields not restricted to conventional ones.

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A02-17-5 Functions produced from space freedom and disorder existing in crystals and their applications

  • Principal Investigator / Katsumi Tanigaki (Tohoku University / Professor)

Special functions can be crated when disorder is introduced in the perfect inorganic and organic single crystals. Such goals in our proposed researches are: (1) Large anharmonicity in phonons is created by the anomalous thermal vibrations of atoms inside the large freedom space in a crystal, which can enable intriguing phonon engineering with very accurate control. (2) Disorder on the surface or in the bulk of organic crystals can provide special disordered states, which enable to inject ambipolar carriers (holes and electrons) simultaneously. These new functions created by disorder in the crystals will realized highly efficient thermoelectrics and very bright light emitting diodes (LED).

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