Heterogeneous wafer bonding of InP/Si at room temperature is studied using surface-activated bonding (SAB) technology. To minimize the degradation of optical property while maintaining enough bonding strength, various bonding conditions including gas species of fast atom beam (FAB) were examined. The results show that a bonding strength of over 0.5 MPa can be obtained with less degradation of photoluminescence (PL) property of InP/Si hybrid wafer by combining Xe and Ar gases for FAB. Using this condition, hybrid wafer including quantum wells were fabricated, which showed sufficient PL property for the fabrication of hybrid photonic devices. The bonding conditions described in this study enabled realization of continuous wave (CW) operation of InP-based layers/SOI hybrid laser.

An optical mode converter between hybrid device and Si waveguide is the key component for efficient and stable operation of III–V/silicon-on-insulator (SOI) hybrid photonic integrated circuits (PICs). In this study, we introduced a double taper structure into such a mode converter and investigated the coupling efficiency dependence on their structural parameters. By using N2 plasma activated bonding technology, III–V/SOI double-taper-type mode couplers with various taper-tip-widths and taper lengths were fabricated, and their coupling efficiencies were evaluated. As the result, a coupling efficiency of as high as −0.2 dB was achieved for a double-taper device with a tip width of 0.4 µm and total length of 85 µm.

In this work, electron beam lithography proximity effect correction (PEC) was experimentally studied for patterning of Si photonic waveguides with a relatively thick resist mask. Beam’s energy density distribution (EDD) was experimentally extracted by the line exposure method; however, exposure lines in this work were developed after cleavage with a high-contrast process to reduce developer-related effects. The measured line spread function was fitted to a 4-Gaussian function to model mid-range energy densities accurately. The extracted EDD showed less proximity effects compared to conventional Monte-Carlo simulation performed by a commercial software. PEC processes with both techniques were experimentally compared for a Si photonic waveguide pattern with different side-cladding trench widths. Microscopic images confirmed that the presented calibration method could achieve better development conditions near the required clearance dosage. Single-mode propagation loss for a 500 × 220 nm Si wire waveguide was reduced from 3.2 to 2.4 dB cm−1 using the presented process.

We have fabricated III-V gain region/Si waveguide hybrid lasers with an InP-based two-storied ridge structure using a direct bonding technology. Continuous-wave operation at a temperature of 20oC with a threshold current as low as 30 mA was obtained for a hybrid laser consisting of a Fabry-Perot cavity with facets formed on the Si waveguide, and it was achieved thanks to a high optical coupling efficiency of over 80% at the interface between the III-V gain region and the Si waveguide using a two-storied ridge structure and a taper waveguide. The wavelength tunable laser which is comprised of a Si cavity with a loop mirror and double ring filters and III-V gain regions with laser and semiconductor optical amplifier (SOA) sections was demonstrated by utilizing this hybrid structure. It exhibited a wide wavelength tuning range of 48.6 nm and an optical amplification of 10 dB by SOA.

To realize next-generation photonic integrated circuits based on the III-V/Si hybrid integration platform using chip-on-wafer (CoW) direct bonding technologies, high-yield collective bonding of InP chips on Si substrates with a high bonding strength is required. This study demonstrates highyield InP/Si CoW plasma-activated bonding using a chip holder with pockets, the depth of which is precisely controlled. Additionally, finite element simulations are used to determine that the stress-controlled interlayer consisting of InP-based epitaxial layers with tensile strain effectively suppresses stress at the InP/Si bonding interface, which affects the bonding strength. Thus, a high bonding strength of 20 MPa in 2 mm × 2 mm InP chips on the Si substrate was achieved by introducing a superlattice structure consisting of GaInAsP and InP (with tensile strain) as the stresscontrolled interlayer. © 2019 The Japan Society of Applied Physics 15 MPa are necessary. 32) This paper exhibits investigation results in the bonding strength of the InP/Si CoW bonding technique using InP-based epitaxial layers with strain introduced as a