RESUMEN
The integration of compact high-bandwidth III-V active devices in a scalable manner is highly significant for Silicon-on-insulator (SOI) photonic integrated circuits. To address this, we demonstrate the integration of pre-fabricated 21 × 57 µm2 InGaAs photodetector (PD) coupons with a thickness of 675â nm to a 500â nm SOI platform using a direct bonding micro-transfer printing process. The common devices are coupled to the Si waveguides via butt, grating and evanescent coupling schemes with responsivities of 0.13, 0.3 and 0.6 A/W respectively, in line with simulations. The thin device facilitates simplified high-speed connections without the need for an interlayer dielectric. A back-to-back data communication rate of 50 Gb/s is achieved with on-off keying and with post processing of four-level pulse-amplitude modulation (PAM4) 100 Gb/s is realized. Potentially, around 1 million devices per 75 mm InP wafer can be attained. The integration of compact PDs exhibited in this work can be extended to modulators and lasers in the future.
RESUMEN
We investigate different architectures for parabolic-graded InGaAs metamorphic buffers grown on GaAs using transmission electron microscopy techniques. The different architectures include InGaP and AlInGaAs/InGaP superlattices with different GaAs substrate misorientations and the inclusion of a strain balancing layer. Our results correlate: (i) the density and distribution of dislocations in the metamorphic buffer and (ii) the strain in the next layer preceding the metamorphic buffer, which varies for each type of architecture. Our findings indicate that the dislocation density in the lower region of the metamorphic layer ranges between 108 and 1010 cm-2, with AlInGaAs/InGaP superlattice samples exhibiting higher values compared to samples with InGaP films. We have identified two waves of dislocations, with threading dislocations typically located lower in the metamorphic buffer (~ 200-300 nm) in comparison to misfit dislocations. The measured localised strain values are in good agreement with theoretical predications. Overall, our results provide a systematic insight into the strain relaxation across different architectures, highlighting the various approaches that can be used to tailor strain in the active region of a metamorphic laser. Supplementary Information: The online version contains supplementary material available at 10.1007/s10853-023-08597-y.
RESUMEN
The objective of this work was to investigate the structure and diversity of lactic acid bacteria (LAB) communities in sourdough used for the production of traditional breads (Carasau, Moddizzosu, Spianata, Zichi) in Sardinia. 16S rDNA sequencing and Randomly Amplified Polymorphic DNA (RAPD-PCR) was applied for the identification and typing of the LAB isolated from 25 samples of sourdoughs. Multivariate statistical techniques were applied to RAPD-PCR pattern to study the biological diversity of sourdough samples. Twelve different species of LAB were identified, and most isolates were classified as facultative heterofermentative lactobacilli. Lactobacillus pentosus dominated the lactic microflora of many samples while Lactobacillus sanfranciscensis was isolated only from a limited number of samples. Although heterofermentative species represented between between 30% and 60% of the isolates in Carasau, Spianata and Zichi sourdoughs, only 2% of the isolates from Moddizzosu sourdoughs were identified as heterofermentative LAB. RAPD-PCR with a single primer followed by cluster analysis did not allow the identification of the isolates at the species level. However, a multidimensional scaling/bootstrapping approach on the RAPD-PCR patterns uncovered the diversity of the LAB communities of LAB showing differences both within and between bread types.