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We demonstrated the enhancement of the optically detected magnetic resonance (ODMR) contrast of negatively charged silicon vacancy (VSi-) in SiC by thermal treatment. To create high density VSi-, Proton Beam Writing (PBW) was conducted. After an annealing at 600 °C, ODMR contrast showed the highest value in the investigated temperature range. At a fewer irradiation fluence, despite no significant change was observed in terms of VSi- PL intensity, the improvement of the ODMR contrast was observed. Considering defect energy levels and annealing behavior previously reported, it was deduced that the improvement of the ODMR contrast was caused by the reduction of other irradiation induced defect centers, such as EH1/EH3 centers., International Conference on Silicon Carbide and Related Materials

We investigated near infrared photoluminescence (PL) spectra at room temperature of irradiated HPSI-4H-SiCs and found that PL ranging from 1100 nm to 1500 nm was strongly associated with the formation of nitrogen vacancy centers in 4H-SiC., International Conference on Silicon Carbide and Related Materials 2019

プロトンビーム描画(PBW)を用いてSiC pnデバイス中に3次元配列VSiの形成を行い、光・電気同時励起時における光学特性を評価した。その結果、光・電気同時励起下では、伝導電子が光励起、ODMRサイクルを阻害(パウリの排他律による)することが示唆された。, 第80回応用物理学会秋季学術講演会

We investigated optical properties, luminescence intensity and optically detected magnetic resonance (ODMR) signal, of three dimensionally (3D) arrayed VSis upon simultaneous optically and electrically excitation. The results revealed that Transited conducting electrons disturb photoexcitation and ODMR by Pauli exclusion principle, which degrades optical properties of VSi under simultaneous excitation, QST IRI Workshop

Color centers which act as stable single photon emitters (SPEs) in wide bandgap semiconductors are key elements for quantum technologies. Silicon carbide (SiC) is regarded as a promising host material for qubit/quantum sensor. It was reported that negatively charged nitrogen-vacancy (NcVsi-) center in SiC (S=1) act as SPS with its zero phonon line (ZPL) around 1170 ~1250 nm. However, detailed characteristics of NcVsi- center in SiC have not yet been clarified since the creation methods for NcVsi- have not yet been established. In this study, various energetic charged particles such as protons, nitrogen (N), silicon (Si) and iodine (I) ions were irradiated into n-type and high purity semi-insulation (HPSI) hexagonal (4H) SiC and subsequently annealed up to 1100C. The creation of NcVsi in SiC are evaluated on the basis of photoluminescence (PL) characteristics., 30th International Conference on Defects in Smiconductors (ICDS-30)

4H-SiC MOSFET チャネルに存在する表面SPSの発光特性ゲート電圧依存性について調べた。MOSFETのしきい値電圧付近で発光強度が増加または減少するSPSが観察された。これは過去の研究例（P8センター)からの類推から、表面SPSの電荷状態がｰ1→ｰ２、0→-1にそれぞれ変化するためと考察した。, 第66回応用物理学会春季学術講演会

4H -SiC 中の窒素・空孔複合欠陥（NVセンター)の形成におけるイオン ビーム照射量・イオン種依存性について調べた。窒素を含む基板では重イオンほどNVセンターが増加するが、窒素をほとんど含まない基板では窒素が最もNVセンターが多かった。これは打ち込んだ窒素自身がNVセンター形成に寄与するためと考察した。, 第66回応用物理学会春季学術講演会

γ線照射が炭化ケイ素表面発光中心(表面SPS)の生成・発光特性に与える影響について調べた。照射量10kGyで表面SPS数が増加、その後はほとんど変化しなかった。フォトルミネッセンススペクトルは照射量に関わらず未照射と明確な差異は認められなかった。これから、γ線照射による界面近傍でのボンド切断とそこに存在する水素、酸素が表面SPSを生成するモデルを考察した。, 第66回応用物理学会春季学術講演会

Comparative study on nonradiative recombination (NRR) centers in InAs/GaAs quantum dot (QD) structure generated by 3 MeV proton irradiation is performed by two wavelength excited photoluminescence (TWEPL). The above-gap excitation (AGE) source of 2.33 eV or 1.26 eV is used to excite GaAs host material or InAs QDs, respectively. The QD PL intensity decreased after irradiation of below-gap excitation (BGE) of 0.75 eV over AGE, indicating a pair of NRR centers activated. The proton irradiation at fluence of 7×1011cm-2 reduces the NRR density, while that of 4×1012cm-2 increases it. Defect formation, carrier injection and their fluence dependence explain experimental results., 第44回光起電力専門家会議(PVSC44)

11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (11th RASEDA) (November 11-13, 2015. City Performing Arts Center), Kiryu, Gunma, Japan, The radiation effect on GaAs p-i-n solar cells with quantum dot (QD) in i-layer was investigated. In previous work, we particularly noted the degradation of fill-factor (FF) for the QD cells. In this work, to clarify the reason of the FF degradation in QD cells, generation current due to low-energy proton irradiation, which we call ion beam induced current (IBIC), was observed to characterize behavior of the generated minority carrier by the protons in the depletion region where QDs are located. The energy of protons was adjusted to damage the depletion region, and decrease of generation current was measured during the proton irradiation. The results suggest that the serious degradation of FF is caused by decrease of the carrier collection efficiency in depletion region due to proton damage., 資料番号: AC1600040000

11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (11th RASEDA) (November 11-13, 2015. City Performing Arts Center), Kiryu, Gunma, Japan, Radiation response is one of the important properties for space solar cells. It should be well understood so as to accurately predict their degradation in orbit and also to improve their radiation tolerance. Recently, a phenomenon, recovery from the radiation degradation by light soaking, on inverted metamorphic (IMM) triple-junction (3J) solar cells was found out. In this work, the light soaking annealing effects on electron irradiated IMM 3J solar cells are reported. IMM 3J solar cells irradiated with 1 MeV electrons with the fluence of 3×10(exp 15) e(-) /cm2 showed the recovery of open-circuit voltage, Voc, up to 43 mV after light (AM0, 1 sun) soaking of 3 hours. The increment of the electroluminescence intensity for InGaP in the IMM 3J cells due to the light soaking suggests that the Voc recovery occurs in InGaP top-cell rather than GaAs middle-cell or InGaAs bottom-cell., 資料番号: AC1600044000

The output parameters of InGaP/GaAs/InGaAs inverted metamorphic triple-junction (IMM3J) space solar cells have been collected for about 3.5 years in orbit. The cells are mounted on “HISAKI” (SPRINT-A) small scientific satellite which was launched on September 14th, 2013. We developed a component to demonstrate next-generation instruments for electrical power systems, and we named it NESSIE (Next-generation Small Satellite Instruments for Electrical Power System). The degradation trends of the IMM3J cells on NESSIE confirmed that the conventional RDC method can be applied to degradation prediction of IMM3J cells which have thin-film structure. To the best of our knowledge, this is the first flight demonstration of IMM3J cells in the world., 27th International Photovoltaic Science and Engineering Conference (PVSEC-27)

Optical measurement techniques allow to evaluate and analyze important device parameters of solar cells without additional sample processing or damage. In this study, we employed photoluminescence (PL) spectroscopy to estimate the external quantum efficiency (EQE) and the minority carrier diffusion length of III-V compound single-junction solar cells. EQE is strictly related to the electroluminescence (EL) signal by the reciprocity theorem. We investigate the relation between the EL and PL signals, and compare the EQE spectra and absorption coefficients derived by our method with those obtained by the conventional approaches. The minority carrier diffusion length of the samples was intentionally changed by irradiation with electrons. We performed numerical simulations to investigate the effect of the minority carrier diffusion length on the PL spectra., 27th International Photovoltaic Science and Engineering Conference (PVSEC-27)

Luminescence centers formed in the vicinity of SiC surface are expected to be utilized as Single Photon Sources (SPSs) because of the high-brightness and the potential of electric control at room temperature. In order to gain more insight into the surface SPSs, 4H-SiC pin-diodes are fabricated and the surface SPSs formed in the pin diodes are investigated using a confocal laser scanning fluorescence microscope (CFM). Locations where the surface SPSs appear as well as photoluminescence spectra of the observed surface SPSs are presented. Antibunching characteristics of the surface SPSs are also investigated by the second order autocorrelation function measurement. We conclude that two different types of surface SPSs appear in the surface of 4H-SiC. The location dependence of the observed surface SPSs indicates that oxide layer on 4H-SiC plays an important role in the formation of surface SPSs, whereas neither ion implantation nor donor ions affected. The peak wavelength of luminescence spectra widely varies depending on their locations, indicating lattice strain introduced by the oxide layer has the potential to affect the luminescence spectra., International Conference on Silicon Carbide and Related Materials 2017

In-plain pi(n-)n diodes were fabricated on n-type epitaxial 4H-SiC layer grown on a n-type 4H-SiC substrate. As a result of confocal photoluminescence measurements, two types of single photon sources were observed in n-type region of 4H-SiC pin diodes, International Union of Materials Research Societies, The 15th International Conference on Advanced Materials (IUMRS-ICAM2017)

We present a study of deep level defects created in isolated ion cascades produced in nitrogen-low-doped 4H-SiC epitaxial layers by implantation of either accelerated H (600 keV) or He (2 MeV) ions using fast-scanning reduced-rate microbeams, in the so-called single ion regime. In the first DLTS measurement, defects labelled as ET2 (0.65 eV) and EH3 (1.06 eV) have been clearly distinguished from the presence of the dominant carbon vacancies (Z1/2 and EH6/7) in increased concentrations for irradiated samples. However, the second DLTS measurement revealed the almost complete removal of ET2 trap and the partial removal of EH3 trap, while the concentrations of Z1/2 and EH6/7 traps have further increased, due to the relatively low temperature annealing up to 700 K, accomplished during the first temperature scan of DLTS measurement. Since majority carrier concentration reduced after irradiation recovers with decreasing ET2 and EH3, those might act as majority carrier removal traps., 29th International Conference on Defects in Semiconductors (ICDS2017)

NCVSi− centers in SiC [nitrogen-vacancy (NV) centers], which produce near-infrared (NIR) photoluminescence (PL) at room temperature, is expected to have applications as quantum sensors for in vivo imaging and sensing. To realize quantum sensing using NV centers, clarification of the formation mechanism as well as control of the high-density formation is necessary. This paper reports a comprehensive investigation on the NIR-PL properties originating from NV centers in high purity semi-insulating and nitrogen (N) contained 4H-SiC substrates formed by ion beam irradiation and subsequent thermal annealing. It is shown that NV centers are exclusively formed by the contained N as impurities rather than the implanted N, and also the heavier ion irradiations induce the NV center formation effectively than the lighter ion irradiations. The study on thermal annealing at different temperatures reveals that the optimal temperature is 1000 °C. From the results of temperature dependence on the PL intensity, it is shown that little thermal quenching of the PL intensity appears at room temperature and the PL signal is collected even at 783 K. The formation mechanism of NV centers is also discussed based on the obtained results.

Lanthanoid-doped Gallium Nitride (GaN) semiconductors are a promising class of materials with the potential to be used across a range of novel quantum optelectronic all-locations including room temperature single photon sources. However, to date there is relatively little understood about the properties of small lanthanoid ensembles, which is required before this class of materials can reach their full potential. This paper reports room temperature optical properties of submicron extent implanted-Praseodymium (Pr) in GaN. Thermal annealing at 1200 °C is conducted for the Pr implanted GaN using SiN cap technique to activate implanted-Pr as luminescent centers. The photoluminescence shows two main peaks at 650.3 and 652.0 nm originating from the 3P0 → 3F2 transition in 4f-shell of Pr3+. We explore the saturation behavior of the photoluminescence intensity. The implanted-Pr activation ratio in a 100 nm × 100 nm region is estimated to be 1.7% in the case of 532 nm excitation.

The radiation degradation characteristic of a multi-junction (MJ) solar cell is more complicated compared to a single-junction (1J) solar cell. To perform the quantitative radiation resistance evaluation of a MJ solar cell, it is necessary to estimate the parameter of subcells in the MJ solar cell, such as the reverse saturation current density (J0), photo current (Iphoto) and shunt resistance (Rsh). In this work, the technique used to estimate each parameter (J0, Iphoto, Rsh) of each of the subcells in the MJ solar cell is suggested by combining the electroluminescence (EL) method, which proposed by Fraunhofer group, and the LED bias light (LBL) method. Furthermore, the decline in the maximum power (Pmax) of the MJ solar cell was predicted on the circuit simulator using this technique before and after 1 MeV electron irradiation., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: AA0061889010, レポート番号: JAXA-SP-12-008E

In this paper, we report that InGaP solar cells irradiated with electrons exhibit a significant recovery of open-circuit voltage after AM0 light soaking. The soaking-light intensity dependence of defect reduction and the change in the carrier concentration profile upon light soaking suggests that the recombination of photogenerated carriers contributes to the recovery. Because 0.2MeV electrons are only responsible for phosphorus recoil in InGaP, the absence of correlation between the activation energy for voltage recovery and the electron irradiation energies of 0.2, 0.4, and 1MeV implies that the annihilation of radiation-induced phosphorus-related defects contributes to the recovery.

Presently long-span void slabs without beams have been used often because of less restriction for making plan. Because of having a long span, large slab makes low natural frequency compared to that with beam, they have a possibility of having a vibration problem. The purpose of these experiments is to establish the way of evaluation of floor vibration, of floor vibration experiment and of design on a aspect of floor vibration. In this paper, we report the result of the analysis of damping constant at a point of design, and explain the damping constant at the natural frequency and about frequency characteristics of damping constants.