Papers by naoteru shigekawa
2013 IEEE International Meeting for Future of Electron Devices, Kansai, 2013
ABSTRACT
Japanese Journal of Applied Physics, 1991
We propose a novel approach (Monte Carlo supercell approach) for investigating the effects of dis... more We propose a novel approach (Monte Carlo supercell approach) for investigating the effects of disorder on the upper-valley electronic properties in an InGaAs ternary alloy. In this approach, the electronic properties in supercells with random atomic configurations are analyzed using the s p 3 s * tight-binding method. Effects of the bond-length difference in the alloy are considered in the present analysis. The effects of disorder on the upper-valley electronic properties have been evaluated by examining the spectral function. The disorder-limited upper-valley electron relaxation time obtained from the spectral function is much shorter than that due to the intervalley-phonon scattering, which indicates that the disorder in the InGaAs alloy induces strong effects on the electron transport properties in high electric fields.
Japanese Journal of Applied Physics
We investigate effects of several-hundred-micron thick luminescence down-shifting (LDS) films com... more We investigate effects of several-hundred-micron thick luminescence down-shifting (LDS) films composed of sol-gel glass with Zn-based nanoparticles (NPs) dispersed on characteristics of Si solar cells. Their internal quantum efficiencies (IQEs) are successfully measured by separating contributions of downshifted photons in measuring reflectance for 300-400 nm, wavelengths of incident photons absorbed by the NPs. We find that IQEs for this wavelength range are more enhanced by employing thicker LDS films, i.e., LDS films with higher optical densities. We also discuss relationship among the number density of NPs in LDS films, their optical properties, and IQEs of cells. We observe a discrepancy between measured and calculated IQEs and indicate escape of downshifted photons across sides of LDS films as its possible origin.
Japanese Journal of Applied Physics
Recent achievements in the research of heterojunctions fabricated using surface activated bonding... more Recent achievements in the research of heterojunctions fabricated using surface activated bonding (SAB), one of the practically useful direct wafer bonding technologies, are discussed. The response of bonding interfaces to post-bonding annealing is focused. These junctions reveal high thermal tolerance (1000 °C in the case of junctions made of widegap materials) despite differences in coefficients of thermal expansion between bonded materials. Defect layers with several nm thickness formed by the surface activation process at the as-bonded interfaces get faint and their electrical and mechanical properties are improved by annealing. These results show that as-bonded interfaces are in a metastable state, and novel functional devices are likely to be realized by applying wafer processing steps to SAB-based junctions. Characteristics of III–V//Si multijunction solar cells, GaN-on-diamond high electron mobility transistors, and metal-foil based low-loss interconnects that are fabricated...
2019 IEEE 46th Photovoltaic Specialists Conference (PVSC)
A GaAs/Si double-junction cell is fabricated by directly bonding a GaAs single-junction cell stru... more A GaAs/Si double-junction cell is fabricated by directly bonding a GaAs single-junction cell structure grown on a GaAs (001) substrate to a n-on-p Si subcell and separating the GaAs substrate using a sacrificial layer etching. Before the sacrificial layer etching, the III-V/Si junction is annealed at 300 ℃ for 1 hour so as to recrystallize the interface and achieve an enough bonding strength based on the results of hard X-ray photoemission spectroscopy. We obtain a bonding yield of ~80% after the sacrificial layer etching. We confirm that the fabricated double-junction cell normally operates by measuring its current-voltage and spectral-response characteristics.
The Japan Society of Applied Physics, Jul 6, 2021
ECS Meeting Abstracts, 2020
Ⅲ-Ⅴ on Si multijunction (MJ) solar cells are promising as next-generation solar cells since they ... more Ⅲ-Ⅴ on Si multijunction (MJ) solar cells are promising as next-generation solar cells since they can provide high efficiency with low cost in comparison with conventional Si and Ⅲ-Ⅴ MJ cells. In fabricating such III-V/Si MJ cells, Ⅲ-Ⅴ subcells are placed on Si bottom cell by hybrid approaches such as surface-activated bonding (SAB). The bonding interfaces with lower interface resistances are strongly required so as to achieve better performance of hybrid MJ cells. It was found that the resistance across the directly-bonded III-V/Si interfaces in MJ cells was higher than the resistance in junctions made of heavily-doped substrates because of the thin heavily-doped bonding layers in actual subcell structures. It was reported that indium tin oxide (ITO) films as intermediate layers between III-V and Si subcells played a role of lowering the series resistance of MJs [1]. It was found, however, that the resistance of GaAs//ITO/Si junctions increased by annealing them [2]. Furthermore, th...
2019 6th International Workshop on Low Temperature Bonding for 3D Integration (LTB-3D), 2019
Direct bonding of diamond and Cu is successfully fabricated by surface activated bonding method. ... more Direct bonding of diamond and Cu is successfully fabricated by surface activated bonding method. An almost full contact area of diamond and Cu is obtained. The effect of annealing temperature on the structure properties of the bonding interface is investigated under in-situ annealing in a transmission electron microscope (TEM).
Proceedings of Symposium on Ultrasonic Electronics
2014 IEEE International Meeting for Future of Electron Devices, Kansai (IMFEDK), 2014
ABSTRACT
2017 IEEE 44th Photovoltaic Specialist Conference (PVSC), 2017
Using surface-activated bonding technologies we fabricate InGaP/GaAs/ITO/Si hybrid triple-junctio... more Using surface-activated bonding technologies we fabricate InGaP/GaAs/ITO/Si hybrid triple-junction (3J) cells with p+-GaAs/ITO and those with n+-GaAs/ITO bonding interfaces. ITO films deposited on the emitter of Si bottom cells work as intermediate layers between III-V and Si sub cells. The samples are not heated during the bonding process. The photovoltaic characteristics of the fabricated 3J cells are compared with characteristics of conventional 3J cells without intermediate layers. The InGaP/GaAs/ITO/Si 3J cells with $n$ + -GaAs/ITO bonding interfaces reveal the highest conversion efficiency and the lowest differential resistance among the investigated 3J cells, which implies the potential of ITO-based intermediate layers for achieving more excellent performances of hybrid multi-junction cells.
ECS Transactions, 2020
We investigate nanostructural properties of GaAs//indium tin oxide (ITO)/Si junctions fabricated ... more We investigate nanostructural properties of GaAs//indium tin oxide (ITO)/Si junctions fabricated by surface-activated bonding with emphasis on impacts of thermal process. Both of the Ga 2p3/2 and As 2p3/2 core-level spectra obtained by hard X-ray photoemission spectroscopy show that the GaAs layers are oxidized by annealing at 400 ℃. This finding is consistent with the formation of amorphous-like layers at 400 ℃ annealed GaAs//ITO interfaces. Concentration depth profiles of O, Ga, and As suggest that the oxidation markedly occurs at GaAs//ITO interfaces annealed at temperatures higher than 200 ℃, which is consistent with the dependence of resistance in GaAs//ITO/Si junctions on annealing temperature. These results suggest that annealing brings about the reaction between GaAs and ITO layers and causes the degradation of the electrical properties of GaAs//ITO interfaces. Lowtemperature process technologies are essential so as to make a full use of ITO as intermediate layers in III-V-on-Si multijunction cells.
2017 5th International Workshop on Low Temperature Bonding for 3D Integration (LTB-3D), 2017
We report on the photoresponse of p-Si/n-SiC heterojunctions and the electrical characteristics o... more We report on the photoresponse of p-Si/n-SiC heterojunctions and the electrical characteristics of SiC/Si heterojunction bipolar transistors (HBTs), both of which are fabricated by bonding SiC and Si layers. We find that in the photoresponse measurements the square root of the quantum yield almost linearly depends on the photon energy and the absorption edge (1.2 V) is close to the bandgap of Si (1.12 eV), which implies that the achieved signal is attributed to the minority electrons optically excited in the p-Si layer and collected in the n-SiC layer across the hetero-interfaces. The characteristics of the SiC/Si HBTs reveal the common-base current gain α of ≈ 0.9 for the base-collector bias voltage of 0 V at room temperature. These results indicate that SiC/Si hetero-interfaces are applicable for novel minority-carrier-based semiconductor devices.
2014 IEEE International Meeting for Future of Electron Devices, Kansai (IMFEDK), 2014
Effects of annealing on GaAs/Si bonding interfaces of III-V-on-Si hybrid tandem solar cells were ... more Effects of annealing on GaAs/Si bonding interfaces of III-V-on-Si hybrid tandem solar cells were investigated. Using a cross sectional transmission electron microscope, an amorphous layer was observed at the interfaces of GaAs/Si junctions that had been fabricated by the surface active bonding method. The amorphous layer vanished after the annealing at 400 °C. We also investigated the effects of the annealing on the current-voltage characteristics of n +-GaAs/n ++-Si and p +-GaAs/n ++-Si junctions.
The Japan Society of Applied Physics, 2020
The Japan Society of Applied Physics, 2019
2017 5th International Workshop on Low Temperature Bonding for 3D Integration (LTB-3D), 2017
We fabricate InGaP/GaAs/Si hybrid triple-junction (3J) cells with different sheet resistances of ... more We fabricate InGaP/GaAs/Si hybrid triple-junction (3J) cells with different sheet resistances of bonding layers in Si bottom cells. We estimate resistances across the p-GaAs/n-Si bonding interfaces of the respective 3J cells by measuring the potentials of the bonding layers. We find that the interface resistances are higher in 3J cells with the bonding layers of Si bottom cells with higher sheet resistances.
2017 International Conference on Electronics Packaging (ICEP), 2017
The possibility of the surface-activated bonding (SAB) technologies for fabricating III-V-on-Si h... more The possibility of the surface-activated bonding (SAB) technologies for fabricating III-V-on-Si hybrid tandem solar cells is discussed. Although the electrical conduction across the bonding interfaces is influenced by the interface states introduced during the surface-activation process, their impacts are likely to be lowered by combining more heavily-doped bonding layers and the annealing process after the bonding. InGaP/GaAs/Si hybrid triple-junction cells are successfully fabricated by bonding III-V heterostructures for InGaP/GaAs double-junction cells and Si cell structures. This means that the bonding interfaces have an enough tolerance against the possible stress during the conventional device process sequence and that the SAB is promising as a practical substitute for the conventional semiconductor growth technologies in fabricating III-V-on-Si tandem cells.
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Papers by naoteru shigekawa