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[Display omitted] • Bonding interface is modified to a homogenous one with an epitaxial layer. • Epitaxial layer constrains the defects, disperses and reduces the heterogenous mismatch stress. • Epitaxial layer is doped to reduce the carrier recombination leakage current in this defect-rich layer. In the realm of optoelectronic integration, silicon-based Ge bonding has attracted great attention due to its advantages in short-wave infrared response and low cost. However, owing to the inherent lattice mismatch and thermal mismatch between Ge and Si, the bonded Ge-Si heterogenous interfaces encountered problems of thermal instability and high interface states. Herein, an approach of separating the bonding interface from the heterogenous interface is proposed through inserting a Ge epitaxial layer (GeEL) between the Si substrate and Ge film. This separation modifies the bonding interface to a homogenous one, alleviating the massive mismatch stress and achieving film relaxation, enhancing bonding stability in all aspects. Moreover, during 850 °C annealing, GeEL is doped via diffusion hence realizes electric filed modulation, inhibiting the carrier recombination leakage current and trap assisted tunneling in this defect-rich layer. A Ge-Si heterogenous PIN diode prepared by this bonding method has achieved a remarkable low dark current density (1.33 mA/cm2), a low ideality factor (1.11), and a high on–off ratio (1 0 6), confirming the outstanding quality of the bonded heterojunction. This work provides great prospects for higher performance, larger scale and multi-functional Si-based heterogenous material device applications. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a hydrophilic sapphire wafer bonding method combining plasma-activation and high-temperature bonding process. It is successfully employed in two sapphire bonding structures, including sapphire direct bonding and sapphire indirect bonding based on an intermediate amorphous Al 2 O 3 (a-Al 2 O 3). Transmission electron microscopy (TEM) results show that the a-Al 2 O 3 turns to be the single crystalline phase due to the induction of the sapphire substrate after high temperature bonding at 1000 °C. Moreover, high bonding strength is achieved for sapphire/sapphire (9.91 MPa) and sapphire/Al 2 O 3 /sapphire (17.96 MPa) structures and exceeds that of the bulk sapphire. This sapphire bonded structure with cavity can be applied to fabricate optical devices and pressure and temperature sensors for extreme high temperature environments. • A hydrophilic sapphire wafer bonding method combining plasma-activation and high-temperature bonding process is demonstrated. • For sapphire/sapphire bonding, the interface achieves a seamless bond on the atomic-scale. • For sapphire/Al 2 O 3 /sapphire bonding, the amorphous Al 2 O 3 turns to be the single crystalline phase. • This sapphire bonded structure with cavity can be applied in extreme high temperature environments. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A de-bondable SiC SiC wafer bonding, compatible with RTA at ∼1273 K, has been accomplished via a Ni nano-film. • The SiC SiC bonding by Ni nano-film achieved at room temperature without any pressure is seamless and robust. • The interfacial precipitation of layered carbon material parallel to the SiC surfaces is considered as the reason of interface weakening and de-bonding. Abstract In this study, a de-bondable wafer bonding method for silicon carbide (SiC) that can sustain rapid thermal annealing (RTA) at ∼1273 K has been realized. Two SiC wafers were bonded via an intermediate nickel (Ni) nano-film at room temperature without any pressure, which was characterized as a seamless and robust bonding. After the RTA process, the strength of the bonding interface was dramatically decreased and the de-bonding could happen at the interface during pulling test. Both of the mechanisms of bonding and de-bonding have been investigated through interface analyses. The sufficient atomic diffusion between two deposited Ni nano-films together with the interfacial mixing between amorphous SiC and the Ni nano-film contribute to the strong bonding of SiC SiC. The interfacial precipitation of layered carbon material parallel to the SiC substrates is assumed to be the reason of the interface weakening and de-bonding after annealing. It is believed that the further development of this bonding and de-bonding technology will advance thin SiC device fabrication, where the RTA process at ∼1273 K is widely used. [ABSTRACT FROM AUTHOR]

[Display omitted] • A polycrystalline Si layer is introduced to eradicate the influence of lattice misfit. • Ar Plasma treatment highly enhanced the bonding strength of InGaAs/Si bonded pair at low temperatures. • A defect-rich region near the epitaxial interface of InGaAs and InP is revealed by depth-dependent and power-dependent photoluminescence (PL) measurements. • A high-quality Si-based InGaAs film is obtained by heterogeneous bonding and wet etching techniques. We report the fabrication of high-quality InGaAs films on Si by wafer bonding at low temperatures (300 ℃). A thin polycrystalline Si (poly-Si) interlayer is introduced between InGaAs and Si to block the lattice mismatch and absorb the bubble by-products produced at the bonded interface using its disordered crystal orientation and gain boundaries. To achieve a high bonding strength, argon plasma treatment was employed on InGaAs and poly-Si surfaces before the pre-bonding process. By using post-wet etching, a defect-rich region near the surface of exfoliated InGaAs film that was initially caused by the thermal mismatch between InGaAs and InP during epitaxy growth can be removed. As a result, a Si-based InGaAs film with a 1.05 MPa bonding strength and bubble-free bonding interface was produced. The defective region is 1.2 μm-thick. After etching the defective area, a high-quality, 1.8 μm-thick Si-based InGaAs film was obtained with an XRD FWHM of 94 arcsec. The results reveal that this method is prospective for the fabrication of high-quality III-V materials on Si, proving that a prospective approach for the fabrication of low-noise InGaAs/Si PIN photodiodes and InGaAs/Si avalanche photodiodes with ultralow dark currents. [ABSTRACT FROM AUTHOR]

[Display omitted] • To overcome serious CTE mismatch, we proposed a room-temperature wafer-bonding method using activated Si atomic-layer for the fabrication of glass- or sapphire-based heterogeneous LiNbO 3 -on-insulator (LNOI) wafer. • We demonstrate the effectiveness of the activated Si atomic-layer as an adhesive for both LiNbO 3 /glass and LiNbO 3 /sapphire. • The tensile strength of the fabricated LNOI wafers exceeded 23 MPa, which indicates that the bond between the LiNbO 3 and glass or sapphire wafers was strong. • The TEM, STEM-EDX, XPS, and TOF SIMS analysis clearly showed the nanostructure and atomic behavior near the bonding interface. We proposed a room-temperature wafer-bonding method using activated Si atomic layer and verify its effectiveness for the fabrication of glass- or sapphire-based LiNbO 3 -on-insulator (LNOI) devices for radio-frequency photonic applications. Four-inch LiNbO 3 was successfully fabricated on glass or sapphire wafers using the proposed method. The tensile strength of the fabricated wafers exceeded 23 MPa, which indicates that the bond between the LiNbO 3 and glass or sapphire wafers was strong. Atomic-structure analysis of bonding interfaces confirmed the effectiveness of the activated Si atomic layer as an adhesive for both LiNbO 3 /glass and LiNbO 3 /sapphire. In addition, the amorphous Si atomic layer existing at the bonding interface showed high transmittance over a wide range of wavelength, including the near-infrared region used for communication. The results demonstrate the potential of the proposed wafer-bonding method for the fabrication of LNOI devices used in optical communications, including broadband traveling-wave modulators. [ABSTRACT FROM AUTHOR]

Room temperature GaN-Si direct wafer bonding was done by surface activated bonding (SAB). At first, a feasibility study using GaN template has been done. Then, crystal-face dependence of the bonding results for freestanding GaN substrate has been investigated between Ga-face and N-face. The results of Ga-face to Si bonding are better than that of N-face to Si bonding such as higher bonding energy and larger bonded area. This difference should be caused by their different surface roughnesses after chemical-mechanical polishing (CMP). Besides, both of the structure and composition of the two kinds of interfaces were investigated to understand the bonding mechanisms. The phenomenon of Ga-enrichment during surface activation and Ga-diffusion into Si at room temperature for both Ga-face bonding and N-face bonding has been confirmed. [ABSTRACT FROM AUTHOR]

This work presents a novel type of surface-enhanced Raman scattering (SERS) devices based on nanocone forests. The nanocone forests are fabricated by using a plasma repolymerization technique, which is a simple and parallel approach that has high reproducibility in wafer-level fabrication. The nanocone forest-based SERS devices exhibit an averaged enhancement factor at the order of 3 × 10 6 , meanwhile, the relative standard deviation of Raman intensity over large areas is around 7%. These experimental results demonstrate great potential of the nanocone forest-based SERS devices in wide applications. [ABSTRACT FROM AUTHOR]

Direct wafer bonds of the material system n-GaSb/n-Si have been achieved by means of a low-temperature direct wafer bonding process, enabling an optical transparency of the bonds along with a high electrical conductivity of the boundary layer. In the used technique, the surfaces are activated by sputter-etching with an argon fast-atom-beam (FAB) and bonded in ultra-high vacuum. The bonds were annealed at temperatures between 300 and 400 °C, followed by an optical, mechanical and electrical characterization of the interface. Additionally, the influence of the sputtering on the surface topography of the GaSb was explicitly investigated. Fully bonded wafer pairs with high bonding strengths were found, as no blade could be inserted into the bonds without destroying the samples. The interfacial resistivities of the bonded wafers were significantly reduced by optimizing the process parameters, by which Ohmic interfacial resistivities of less than 5 mΩ cm 2 were reached reproducibly. These promising results make the monolithic integration of GaSb on Si attractive for various applications. [ABSTRACT FROM AUTHOR]

Chemical mechanical polishing (CMP) removal mechanisms of on-axis Si-face SiC wafer have been investigated through X-ray photoelectron spectroscopy (XPS), UV–visible (UV–vis) spectroscopy and atomic force microscopy (AFM). XPS results indicate that silicon oxide is formed on Si-face surface polished by the slurry including oxidant H 2 O 2 , but not that after immersing in H 2 O 2 solution. UV–vis spectroscopy curves prove that •OH hydroxyl radical could be generated only under CMP polishing by the slurry including H 2 O 2 and abrasive, so as to promote oxidation of Si-face to realize the effective removal; meanwhile, alkali KOH during CMP could induce the production of more radicals to improve the removal. On the other side, ultra-smooth polished surface with atomic step structure morphology and extremely low Ra of about 0.06 nm (through AFM) is obtained using the developed slurry with silica nanoparticle abrasive. Through investigating the variations of the atomic step morphology on the surface polished by different slurries, it's reveals that CMP removal mechanism involves a simultaneous process of surface chemical reaction and nanoparticle atomic scale abrasion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dislocation network is revealed in Ge of Ge/Si bonded pair for the first time. • An amorphous Si layer is introduced to eradicate influence of lattice misfit. • Thermal stress is proved to be driving force for dislocation nucleation. • A theoretical model is constructed clarifying the nucleation mechanism. We report nucleation of dislocations in Ge of Ge/Si bonded pairs annealed at low annealing temperatures (≤400 oC). Two types of dislocation networks are revealed near Ge/Si bonded interface for the first time, including sparsely distributed dislocations (type-I) and criss-crossingly arranged ones (type-II). A thin amorphous Si (a-Si) intermediate layer is introduced at the Ge/Si bonded interface to eradicate the influence of the lattice misfit between Si and Ge, and the thermal stress is proved to be the driving force for nucleation of both types of dislocation. Impact of annealing temperature on dislocation nucleation is identified. It is observed that type-I dislocations constitute the majority of dislocations in Ge wafer of bonded pairs annealed at annealing temperature range 275–350 ℃, and type-II ones start to prevail at annealing temperature range 350–400 °C. A kinetic model that accommodates the strain relaxation process and behavior of dislocation is constructed based on fundamental strain and dislocation theory. By fitting the experimental data, it is proposed that heterogeneous nucleation caused by "initial nucleation sites" correlated with surface fluctuation and pretreatment is dominant for dislocation nucleation at low annealing temperature range, and multiplication mechanism activated by secondary nucleation sites, such as Frank-Read sources, incurs the booming of dislocation density (DD) at elevated temperatures. This finding may cast light on the nature of crystallinity degradation of Ge wafers integrated on Si substrate by a hybrid wafer bonding technology. [ABSTRACT FROM AUTHOR]

• A non-toxic, inorganic adhesive material called water glass was investigated. • High-concentration adhesive layer was realized and then applied to wafer bonding. • Desirable and stable bonding strength was achieved. • Air-plasma treatment extend the bonding method to hydrophobic surfaces. An air-plasma enhanced low-temperature wafer bonding method using high-concentration water glass adhesive layer has been demonstrated. The high-concentration water glass adhesive layer for wafer bonding has been achieved by introducing nitrogen and preventing CO 2 , and successfully bonded using spot pressing bonding and air-plasma enhancement for the first time. The tensile strength of the bonded pairs was about 15 MPa and maintained even after long-term storage. The influence of air-plasma treatment was investigated by comparing the contact angles of different substrates and storage time after air-plasma treatment. In addition, the influence of the carbon residue in different preparation conditions were also investigated by X-ray photoelectron spectroscopy (XPS), current-voltage (I-V) and capacitance-frequency (C-f) measurements. The samples coated in nitrogen have lower intensity of carbon, higher leakage current density and lager dielectric constant comparing to the samples coated in the air. Therefore, the bonding method is a promising method for low-temperature bonding with high-concentration adhesive. [ABSTRACT FROM AUTHOR]