III-V Light-Emitting Diodes on Silicon by Hydrogel-Mediated Wafer Bonding

Monolithic on-chip integration of III–V compound semiconductor light-source components particularly on Si platforms is thought to be an important key technology in modern optoelectronics. Hydrogel-mediated semiconductor wafer bonding is an emerging technique for heterogeneous materials integration, simultaneously forming interfaces with high mechanical stability, electrical conductivity, optical transparency, and surface-roughness tolerance [K. Kishibe and K. Tanabe, Appl. Phys. Lett., 115, 081601 (2019)]. So far, its experimental demonstration has been limited to homogeneous Si/Si bonding and an application of solar-cell device. Here we demonstrate the fabrication and operation of a III–V light-emitting diode on Si, via heterogeneous GaAs/Si hydrogel-mediated wafer bonding. The bonding process is carried out in ambient air at room temperature, and therefore can potentially provide significant cost and throughput advantages in device production. Bonding with an unpolished back surface of semiconductor wafer with a micrometer-scale roughness is realized thanks to the deformability of hydrogel. The luminescence characteristics of the bonded device on Si are measured comparable to an unbonded reference. Stable operations of the device at over 70 °C and for over 100 h are demonstrated. Our experimental results verify the further suitability of the hydrogel-mediated semiconductor bonding scheme for optoelectronic device applications

Graphene-Quantum-Dot-Mediated Semiconductor Bonding: A Route to Optoelectronic Double Heterostructures and Wavelength-Converting Interfaces

A semiconductor bonding technique that is mediated by graphene quantum dots is proposed and demonstrated. The mechanical stability, electrical conductivity, and optical activity in the bonded interfaces are experimentally verified. First, the bonding scheme can be used for the formation of double heterostructures with a core material of graphene quantum dots. The Si/graphene quantum dots/Si double heterostructures fabricated in this study can constitute a new basis for next-generation nanophotonic devices with high photon and carrier confinements, earth abundance, environmental friendliness, and excellent optical and electrical controllability via silicon clads. Second, the bonding mediated by the graphene quantum dots can be used as an optical-wavelength-converting semiconductor interface, as experimentally demonstrated in this study. The proposed fabrication method simultaneously realizes bond formation and interfacial function generation and, thereby, can lead to efficient device production. Our bonding scheme might improve the performance of optoelectronic devices, for example, by allowing spectral light incidence suitable for each photovoltaic material in multijunction solar cells and by delivering preferred frequencies to the optical transceiver components in photonic integrated circuits

An all ambient, room-temperature processed solar cell from a bare silicon wafer

大気中かつ室温での太陽電池の作製を実現 --低コストで簡便に太陽電池の製造が可能に--. 京都大学プレスリリース. 2023-03-15.Solar cells charging forward: Realizing the potential of creating silicon-based photovoltaics at room temperature. 京都大学プレスリリース. 2023-04-11.Solar cells are a promising optoelectronic device for the simultaneous solution of energy-resource and environmental problems. However, their high cost and slow, laborious production process so far severely hinder a sufficient widespread of clean, renewable photovoltaic energy as a major alternative electricity generator. This undesirable situation is mainly attributed to the fact that photovoltaic devices have been manufactured through a series of vacuum and high-temperature processes. Here we realize a PEDOT:PSS/Si heterojunction solar cell fabricated only in ambient and room-temperature conditions from a plain Si wafer, with an over-10% energy conversion efficiency. Our production scheme is based on our finding that PEDOT:PSS photovoltaic layers actively operate even on highly doped Si substrates, which substantially mitigates the condition requirements for electrode implementation. Our approach may pave the way for facile, low-cost, high-throughput solar cell fabrication, useful in various fields even including developing countries and educational sites

Selective Transfer of Si Thin-Film Microchips by SiO₂ Terraces on Host Chips for Fluidic Self-Assembly

Fluidic self-assembly is a versatile on-chip integration method. In this scheme, a large number of semiconductor microchips are spontaneously deposited onto a host chip. The host chip typically comprises a Si substrate with an array of pockets at the designated microchip placement sites. In this study, we installed an SiO₂ layer on the terrace region between the pockets of the host chip, to reduce the attraction with the Si microchips. By the SiO₂-topped terrace scheme, we demonstrated a significant enhancement in the deposition selectivity of the Si microchips to the pocket sites, relative to the case of the conventional Si-only host chip. We theoretically explained the deposition selectivity enhancement in terms of the van der Waals interaction. Furthermore, our quantitative analysis implicated a potential applicability of the commonly used interlayer dielectrics, such as HfO₂, silsesquioxanes, and allyl ethers, directly as the terrace component

Effect of oxygen in shielding gas on weldability in plasma-GMA hybrid welding process of high-tensile strength steel

The version of record of this article, first published in International Journal of Advanced Manufacturing Technology, is available online at Publisher’s website: https://doi.org/10.1007/s00170-024-14100-x.This study aims to clarify the effect of oxygen in shielding gas on weldability in the plasma-GMA (Gas Metal Arc) hybrid welding process of high-tensile strength steel plates. The difference in keyhole profile and bead formation, when the GMA shielding gas was pure Ar, Ar + 2% O₂ or Ar + 20% CO₂, was investigated for plate thicknesses of 6 and 9 mm for the first time. It was found that the weld beads were in good condition for 6 mm thickness plates for all shielding gases, which implied that the window of welding conditions for this thickness is wide. In contrast, for 9 mm thickness plates, a fully penetrated weld bead was achieved only in Ar + 20% CO₂, and weld bead penetration in Ar + 20% CO₂ is higher than in pure Ar and Ar + 2% O₂ in the same welding condition. Due to decreased surface tension caused by sufficiently increased oxygen absorbed into the weld pool, the keyhole diameter increased to penetrate the bottom side of the plate, and the depressing weld pool surface under GMA allowed the heat input from the GMA to be directly applied to a deeper position. Consequently, the plasma-GMA hybrid welding process with Ar + 20% CO₂ achieved a complete penetration for a plate of 9 mm thickness, owing to the effects of both phenomena. It proved a potential to increase penetrability in welding thicker plates by controlling oxygen content in shielding gas of GMA adequately

The Effect of Medical Cooperation in the CKD Patients: 10-Year Multicenter Cohort Study

Introduction: While chronic kidney disease (CKD) is one of the most important contributors to mortality from non-communicable diseases, the number of nephrologists is limited worldwide. Medical cooperation is a system of cooperation between primary care physicians and nephrological institutions, consisting of nephrologists and multidisciplinary care teams. Although it has been reported that multidisciplinary care teams contribute to the prevention of worsening renal functions and cardiovascular events, there are few studies on the effect of a medical cooperation system. Methods: We aimed to evaluate the effect of medical cooperation on all-cause mortality and renal prognosis in patients with CKD. One hundred and sixty-eight patients who visited the one hundred and sixty-three clinics and seven general hospitals of Okayama city were recruited between December 2009 and September 2016, and one hundred twenty-three patients were classified into a medical cooperation group. The outcome was defined as the incidence of all-cause mortality, or renal composite outcome (end-stage renal disease or 50% eGFR decline). We evaluated the effects on renal composite outcome and pre-ESRD mortality while incorporating the competing risk for the alternate outcome into a Fine-Gray subdistribution hazard model. Results: The medical cooperation group had more patients with glomerulonephritis (35.0% vs. 2.2%) and less nephrosclerosis (35.0% vs. 64.5%) than the primary care group. Throughout the follow-up period of 5.59 +/- 2.78 years, 23 participants (13.7%) died, 41 participants (24.4%) reached 50% decline in eGFR, and 37 participants (22.0%) developed end-stage renal disease (ESRD). All-cause mortality was significantly reduced by medical cooperation (sHR 0.297, 95% CI 0.105-0.835, p = 0.021). However, there was a significant association between medical cooperation and CKD progression (sHR 3.069, 95% CI 1.225-7.687, p = 0.017). Conclusion: We evaluated mortality and ESRD using a CKD cohort with a long-term observation period and concluded that medical cooperation might be expected to influence the quality of medical care in the patients with CKD