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Monolithic two-terminal III-V on Si dual-junction solar cells, designed for low concentration applications, were fabricated by means of surface-activated direct wafer bonding. The III-V top cell is a heterojunction formed by an n-Ga 0.5 In 0.5 P emitter and a p-Al 0.2 Ga 0.8 As base. An efficiency of 21.1 ± 1.5% at one sun and 23.7 ± 1.7% at 10 suns is demonstrated, which to our knowledge is the best dual-junction twoterminal III-V on Si tandem cell efficiency reported to date under verified reference conditions. The I-V characterization of these 1-cm 2 tandem cells under concentration required the development of a new method using a single-source multiflash solar simulator and not perfectly matched component cells, also known as pseudoisotypes, formed by Si single-junction cells and optical filters. In addition, the spectrum of the pulsed solar simulator was measured using a high-speed CMOS spectrometer, allowing the calculation of the spectral mismatch correction factor. Merging these two techniques results in the hybrid corrected pseudo-isotype (HCPI) characterization method, which shows a fast and accurate performance with a simplified procedure based on a single-source solar simulator. Pseudo-isotypes are easily adaptable to new cell designs by simply using a different filter, hence allowing the characterization of new multijunction solar cell architectures.

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Hybrid integration of III-V materials onto silicon by wafer bonding technique is one of the mature and promising approaches to develop advanced photonic integrated devices into the silicon photonics platform (SPP). Epitaxial regrowth of III-V materials on InP thin seed layer bonded to an oxidized silicon wafer has shown its potential to extend the III-V mature multiregrowth technologies into the SPP. In the approach, an epitaxial InP layer grown on a 4 in. InP wafer is directly bonded onto a SiO 2 /Si 200 mm wafer. After InP substrate removal, the new template (InPoSi) is evaluated for epitaxial regrowth: an eight periods strain-compensated AlGaInAs multiquantum wells (MQW) heterostructure surrounded by two InP cladding layers is grown by metal-organic vapor phase epitaxy (MOVPE) simultaneously on the InPoSi substrate and on an InP substrate as a reference. For the first time, in situ reflectance and curvature measurements are carried out on InPoSi, enabling the assessment of surface roughness and thermal strain of the III-V materials during growth. High material quality is obtained as attested by X-ray diffraction, photoluminescence, atomic force microscopy, and transmission electron microscopy.