Hideo ISSHIKI (一色 秀夫)

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 7200000, indirect: -)
The objectives of this study is to make an Er/SiO_2/Si ultra thin multilayer structure and to measure the energy transfer between carriers in Si and Er as a function of the thickness of the oxide layer which separates carriers and Er, in order to make clear the physical meanings of the effect of the oxide interlayer for the strong Er-related 1.54 μm emission at room temperature and to obtain a design principle for room temperature 1.54 μm luminescent devices.
First, the energy transfer from photocarriers generated in Si to Er^<3+> ions is measured from the photoluminescence intensity and fluorescent decay time of the 1.54 μm emission as a function of the thickness of the oxide interlayer. Next, the reduction of the decay time under the cw illumination due to Auger quenching is measured to estimate the energy backtransfer from Er^<3+> ions to photocarriers.
It is found that, though both the energy transfer and backtransfer are decreased with increasing the oxide thickness, the latter is decreased much more rapidly. In addition, it is shown that the energy transfer between carriers and Er^<3+> ions is due to the exchange mechanism. In conclusion, a thin oxide layer of 〜 2nm thickness improves the temperature quenching (γ = I_<300K>/I_<20K> = 1/2 〜 1/3 ) and gives the strongest room temperature intensity of the Er-related 1.54 μm luminescence.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 4000000, indirect: -)
Final goal of this study is to develop optoelpctronic devices and the integration on silicon (Si) for optical fiber communications with WDM technologies. At the first, fabrication process of erbium (Er) doped waveguide for photonic circuits on silicon substrates has been developed. The applications of porous silicon (PS) to make rare earth doped silicon related materials for optoelectronic devices and the integration are expected. The anodic etching process is a main process for PS fabrication, and requires holes in Si. In this study, we propose the modified anodic etching process to form two-dimensional multi-layered nano-PS. Making a back contact on an n-Si substrate as the source of hole supply, the nano-pores grow perpendicular to the substrate surface. Then a hole-blocking layer is formed selectively on the substrate by ion implantation so that nano-PS on selective area can be obtained. Also we have developed an optical activation process of Er ions doped in Si, which is combined rapid oxidation and rapid thermal annealing processes (RTOA). Due to the activation process, thermal quenching of Er related emissions were remarkably reduced so that 1.54 μm intense PL emissions at room temperature were observed. From 2001, we began to study on Er doped Si photonic crystals with Prof. A Polman of FOM-AMOLF in the Netherlands. By using the RTOA process, room temperature 1.54 μm emissions of Er ion doped in Si photonic crystal were observed under electron-hole pair mediated excitations. Furthermore we have found out novel optoelectronic material "ErSiO natural superlattice" under investigation of the RTOA process. The novel material shows fine structure (Stark splitting) of emission and absorption spectra relative to Er ions, intense emission at room temperature and semiconductor nature. On the other hands, metal-organic vapor phase epitaxy (MOVPE) for SiGe is successfully realized for the first time. Ge dot and Si/SiGe superlattice applied to integrated photo detectors were formed on Si substrates by MOVPE.

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業, Category: 特定領域研究(B), Fund Type: -, Overall Grant Amount: - (direct: 51600000, indirect: -)
高配向性グラファイトに多価のアルゴンイオンを照射することにより、ナノサイズのダイヤモンドの創製が可能なことが、本研究の成果として得られたが、本年度はさらに作成した構造が本来持っていない新たな特性を示すことを明らかにした。高配向性グラファイトに8価のアルゴンイオンを照射した後、He-Cdレーザーを照射しイオン照射領域をsp^3を有するナノダイヤモンド様の構造に変化させ、さらにその構造を水素雰囲気中で600℃、30分間の熱処理を施すことにより、複数の特性に顕著な変化が見られた。グラファイトは可視域、紫外域には発光を示さない材料であるが、20Kで測定したカソードルミネッセンスでは、微弱ながら紫外域に発光を示すことが分かった。また、イオン照射領域に対して走査トンネル顕微鏡を用いて電界放出効果を調べたところ、化学気相成長法で作成した多結晶ダイヤモンド薄膜と同等の電界放出特性を示すことも確認された。これらの結果は、ナノスケールでの新しい材料創製を示唆する結果と考えられる。また、ラマン分光法を用いて多価イオン照射の高配向性グラファイト基板に対する効果を調べた結果、同程度のドーズ量では価数が高くなるにつれて、ディフェクティブなスペクトルが得られた。これは、価数が低い場合には、イオン照射により点欠陥が生成されるが、価数の増加に従い点欠陥の複合体が形成されることを示している。
また、レーザーアブレーションによりナノ構造シリコン(Siナノ微粒子)を創製し、気相での水素表面修飾、および固相でのErとPの不純物をドーピングを試み、Siナノ微粒子の形成過程については第2レーザー照射法により時間分解PL測定を行ない、その動的過程を明らかにし、Erドーピングにより温度消光のないSiナノ結晶の作製とPドナーのSiナノ結晶へのドーピングの可能性を示した。

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業, Category: 国際学術研究, Fund Type: -, Overall Grant Amount: - (direct: 3200000, indirect: -)
1.試料作製
原子層エピタキシ-法とビームリソグラフィー技術により試料作製を行った。幅が20-30nmの量子細線構造、および、周期150nm幅が25nmチタン/金電極を用いたスプリットゲート法による試料を作製した。これは報告されている試料の中では最小の周期を持つものであり、電子相互作用の観測に適したものと考えられる。
2.測定
輸送現象の測定により閉じ込め構造中の電子密度を測定した。また、強磁場下の光学スペクトルの測定を試料温度を1.9Kから150Kの範囲で行ない、量子閉じ込め構造中の電子密度分布に関する知見を得た。
3.理論解析
実験に使用した試料形状を再現するようなモデル計算をハートレー近似の範囲で行い、電子密度分布を解析した。得られた結果は測定の結果をよく再現した。

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 2300000, indirect: -)
Er ions doped in Si nanometer-sized materials give rise to intense 1.54mum emission at room temperature. The motivation of this study is to apply the Er-doped nanocrystalline Si to new optical devices and memories. Main results of this project are shown in bellow.
(1).Size control of Si nanocrystallites by using Eras a nucleation center
Size control of Si nanocrystallites formed in n-Si matrix is achieved by using Er as a nucleation center. We have fabricated a series of nc-Si samples with size from 3 nm to 10 am. The smallest crystallite size was 2.7 nm. a Si dot including -1000 atoms. The nc-Si layers are homogeneous both in the crystallite size and in the optoelectronic properties. The samples show a blue emission band and a sharp peak at 1.54mum up to room temperature. We showed that the blue emission shift to higher energies with decreasing size which is in good agreement with the absorption data and could be explained by a novel quantum size effect.
(2).Room-temperature 1.54 mum emission from Er-doped porous Si
Er was doped into porous Si by immersing the porous Si sample in a saturated ErCl_3 : ethanol solution. Sharp and intense 1.54 mum photoluminescence caused by intra-4f-shell transitions in Er^<3+> ions was observed up to room temperature. Time resolved study of the Er-doped porous Si revealed that the doped Er^<3+> ions were excited by energy transfer from electron-hole pairs in the host. The energy back transfer process is not a dominant factor to quench the Er-related emission in porous Si. A probe effect of measuring the absorption edge of the host by Er emission was proved both for porous Si and nc-Si. Our results were well explained by a proposed model in which an intermediate state was introduced.
(3).An Er-doped nc-Si laser operated at room temperature
Er-doped nc-Si waveguides were fabricated on Si substrates. A stimulated emission at 1.54 mum was demonstrated at room temperature. The sizes of the fabricated Er-doped nc-Si waveguides were 5000 nm x 200 nm x L, where L is the cavity length and is changed from 1 mm to 10 mm. This is the first breakthrough of realizing an all-Si laser.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 7600000, indirect: -)
Electronic states in usual periodic structures are given by the periodicity like Bloch theorem. Introducing non-periodicity into the lattice, the electronic states with singular coherency of electron wavefunctions can be expected. We have focused on the periodic modulation (Fractal etc.) of lattice, and carried on the fablication and the characterization of periodic-modulated superlattices, as novel functional materials. The results of this study are summarized as follows.
(1)Development of atomic-layer manipulation technologies for superlattice : (GaAs)m(GaP)n and (AIP)m(GaP)n atomic-layer superlattices have been successfully realized by atomic layer epitaxy(ALE), and also the inter-diffusion between the mono-layer lattice has been discussed.
(2)Periodic modulation of superlattice with atomic-layer accuracy : GaAs/GaP and AlP/GaP periodic-modulated superlattices have been successfully realized with atomic-layer accuracy by the ALE technologies. Periodic, quasi-periodic (Fractal), random, and multi-periodic structures have been used as the modulated structures, and especially Fibonacci progression has been used as Fractal structures.
(3)X-ray analysis of the periodic-modulated superlattices : The XRD pattern of quasi-periodic superlattice shows no periodicity but self-similar geometry, and is consistent with the FFT spectrum of a Fractal structure. Also the X-ray reflection measurement of multi-periodic superlattice shows that the reflection wavelength can be controlled with sub-monolayer accuracy by modulation of the periodicity. This suggests the possibility of application to X-ray mirrors.
(4)Optical characterization of electronic states in the periodic-modulated superlattices : Photo-reflectance spectrum of quasi-periodic, random superlattices show peculiar splitting of the subband (electronic states) in comparison with that of the periodic lattice, and are consistent with a transfer matrix calculation for the lattices. This result suggests that the control of electronic state can be possible artificially due to the periodic modulation using the ALE technologies.
(5)Application to X-ray mirrors : We have discussed the application of periodic modulation for the lattice to X-ray mirror. Introducing the multiple period into atomic layer superlattice, the reflection wavelength can be controlled arbitrary with sub-monolayer accuracy that is needed to X-ray mirrors.

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業, Category: 奨励研究(A), Fund Type: -, Overall Grant Amount: - (direct: 900000, indirect: -)
原子層成長(ALE)を用いた低次元量子構造作製プロセス開発を目的としてALE選択成長機構解明に重点を置き,ALE技術の潜在能力を引き出し新たなプロセス技術を開発した。更にALE選択成長により作製した微細量子構造の基礎的な光物性評価を行い明確な一次元閉じ込め効果を観測した。本年度の成果は以下のとおりである。
(1)成長モード切り替え技術の開発、極微細領域中の局財ALE成長の機構解明
ALEにおける面方位選択成長機構を解明した。この結果、成長シーケンスによりALE成長中の表面反応の選択的な制御が可能であることを見出し、ALE成長モード切り替え(isotropic〈-〉anisotropic)技術を確立した。さらに低次元量子構造を作製するうえで重要となる極微細領域における成長速度の変動についても検討を行った。そしてALEの特徴である自己停止機構によりナノメートルエリアにおいても異常成長がなく原子層制御可能な局在ALE成長が可能であることを示した。
ALE成長モード切り替え技術を用いた低次元量子構造作製プロセスの開発
上記の結果をもとに、さらに赤外光照射効果によるALE成長中における炭素原子混入の低減化を組み見合わせて、構造及び組成の原子層制御が可能である低次元量子構造作製プロセスを開発し、矩形量子細線の作製に成功した。
(3)低次元構造における量子サイズ効果の観測、解析
ALE選択成長により作製した矩形量子細線からのフォトルミネッセンス(PL)発光を観測し、そのPLスペクトル及び偏光依存性(光学的異方性)から一次元閉じ込め効果を観測した。また、量子細線構造特有の価電子帯における電子状態の観測に成功した。

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業, Category: 重点領域研究, Fund Type: -, Overall Grant Amount: - (direct: 2500000, indirect: -)
本年度は原子層成長(ALE)を用いた低次元量子構造作製プロセス開発を目的としてALE選択成長機構解明に重点を置き、ALE技術の潜在能力を引き出し新たなプロセス技術を開発した。更にALE選択成長により作製した微細量子構造の基礎的な光物性評価を行い明確な一次元閉じ込め効果を観測した。本年度の成果は以下のとおりである。
(1)成長モード切り替え技術の開発、極微細領域中の局在ALE成長の機構解明
ALEにおける面方位選択成長機構を解明した。この結果、成長シーケンスによりALE成長中の表面反応の選択的な制御が可能であることを見出し、ALE成長モード切り替え(isotropic〈-〉anisotropic)技術を確立した。さらに低次元量子構造を作製するうえで重要となる極微細領域における成長速度の変動についても検討を行った。そしてALEの特徴である自己停止機構によりナノメートルエリアにおいても異常成長のない均一な局在ALE成長が可能であることを示した。
(2)ALE成長薄膜の結晶性向上
結晶成長中における炭素原子混入の低減について検討を行った結果、GaAsALE成長において赤外光照射が有効であることを示した。
(3)ALE成長モード切り替え技術を用いた低次元量子構造作製プロセスの開発
上記(1),(2)の結果をもとにALEを用いた低次元量子構造の作製プロセスを開発し、矩形量子細線の作製に成功した。
(4)低次元量子構造における量子サイズ効果の観測、解析
ALE選択成長により作製した矩形量子細線からのフォトルミネッセンス(PL)発光を観測し、そのPLスペクトル及び偏光依存性から一次元閉じ込め効果を観測した。また、量子細線構造特有の価電子帯における電子状態の観測に成功した。

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for General Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 7300000, indirect: -)
Advanced technologies of controlling low-dimensional quantum structures (i.e.size, shape, composition, arrangement and doping control) with atomic-level accuracy were developed, based on atomic layr epitaxy (ALE) selective gwowth, for the future quantum devuces. The results o this study are summarized as follows.
(1) Growth mechanism of localized-ALE in nano-space, and layr-by-layr growth mode switching technique
It has been found that ALE selective growth makes the control of semiconductor structures possible even in nanometer scale area (Localized-ALE), which is due to the self-limiting effect. Also layr-by-layr growth mode switching technique between anisotropic and isotropic ALE growth, using control of the growth sequence, was developed with the concept as a "selective-control of surface-processes".
(2) Development of fabrication processes of low-dimensional quantum structures using ALE growth mode switching technique
Fabrication processes of low-dimensional quantum structures were developed, and rectangular shaped quantum wire structures were successfully realized. In this study, the fabrication of low dimensional atomic layr short-period superlattice by using the advanced ALE techniques were demonstrated, for the control of "conposition" and "arrangement" in quantum nano-structures.
(3)Development of Digital-etching : Control of surface reaction by tunable UN laser
Digital-etching of GaAs using tunable UV laser was discussed. It was found that alternative procedures between feed the enchant (Cl_2) and laser beam irradiation with precious wavelength is necessary to realize the self-limiting effect in digital etching process.
(4) Observation and analysis of quantum size effects in low-dimensional quantum structures.
Photoluminescence (PL) measurements on GaAs/GaAsP rectangular shaped quantum wires have been performed. One dimensional (1D) confinement effect on the structures has been confirmed by the PL emission and the polarization dependence of the PL spectra. Also the particular electronic states on valence band in the wires, whhich is due to the band mixing effect, was observed by the PL emission from the p-type modulation doped wire structures. Diamagnetic shift of PL emission from the wires also observed.