Detection and Genetic Environment of Pleuromutilin-Lincosamide-Streptogramin A Resistance Genes in Staphylococci Isolated from Pets

Increasing emergence of staphylococci resistant to pleuromutilins, lincosamides, and streptogramin A (PLSA) and isolated from humans and pets is a growing public health concern worldwide. Currently, there was only one published study regarding one of the PLSA genes, vga(A) detected in staphylococci isolated from cat. In this study, eleven pleuromutilin-resistant staphylococci from pets and two from their owners were isolated and further characterized for their antimicrobial susceptibilities, plasmid profiles, genotypes, and genetic context of the PLSA resistance genes. The gene sal(A) identified in 11 staphylococcal isolates was found for the first time in Staphylococcus haemolyticus, Staphylococcus epidermidis, and Staphylococcus xylosus. Moreover, these 11 isolates shared the identical regions flanking the sal(A) gene located in the chromosomal DNA. Two S. haemolyticus isolates from a cat and its owner carried similar vga(A)LC plasmids and displayed indistinguishable PFGE patterns. A novel chromosomal multidrug resistance genomic island (MDRGI) containing 13 resistance genes, including lsa(E), was firstly identified in S. epidermidis. In addition, vga(A)LC, sal(A), and lsa(E) were for the first time identified in staphylococcal isolates originating from pet animals. The plasmids, chromosomal DNA region, and MDRGI associated with the PLSA resistance genes vga(A), vga(A)LC, sal(A), and lsa(E) are present in staphylococci isolated from pets and humans and present significant challenges for the clinical management of infections by limiting therapeutic options

The growth of low-threading-dislocation-density GaAs buffer layers on Si substrates

Monolithic integration of III-V optoelectronic devices on Si platform is gaining momentum, since it enables advantages of low cost, less complexity and high yield for mass production. With the aim of achieving advances in monolthic integration, the challenges associated with lattice mismatch between III-V layers and Si substrates must be overcome, as a low density of threading dislocations is a prerequisite for the robustness of the integrated devices. In this paper, we have investigated and compare different tyeps of dislocation filter layers (DFLs) from InGaAs asymmetric step-graded buffer layer (ASG), InGaAs/GaAs strained-layer superlattices, and quaternary alloy InAlGaAs ASG, on the functionlity of reducing threading dislocation density (TDD) for GaAs buffer layers on Si. Compared to other DFLs, the sample with InAlGaAs ASG buffer layer shows the lowest average TDD value and roughness, while the deccrease of TDD in the sample with InAlGaAs ASG buffer layer can be understood in terms of the hardening agent role of aluminium in the InAlGaAs ASG. By further optimising the InAlGaAs ASG through thermal cyclic annealing, we successfully demonstrate a low surface TDD of 6.3±0.1×106 /cm2 for a 2 µm GaAs/InAlGaAs ASG buffer layer grown on Si. These results could provide a thin buffer design for monolthic integration of various III-V devices on Si substrates

From Challenges to Solutions, Heteroepitaxy of GaAs-Based Materials on Si for Si Photonics

Monolithic growth of III-V materials onto Si substrates is appealing for realizing practical on-chip light sources for Si-based photonic integrated circuits (PICs). Nevertheless, the material dissimilarities between III-V materials and Si substrates inevitably lead to the formation of crystalline defects, including antiphase domains (APBs), threading dislocations (TDs), and micro-cracks. These nontrivial defects lead to impaired device performance and must be suppressed to a sufficiently low value before propagating into the active region. In this chapter, we review current approaches to control the formation of defects and achieve high-quality GaAs monolithically grown on Si substrates. An APB-free GaAs on complementary-metal-oxide semiconductor (CMOS)-compatible Si (001) substrates grown by molecular beam epitaxy (MBE) only and a low TD density GaAs buffer layer with strained-layer superlattice (SLS) and asymmetric step-graded (ASG) InGaAs layers are demonstrated. Furthermore, recent advances in InAs/GaAs quantum dot (QD) lasers as efficient on-chip light sources grown on the patterned Si substrates for PICs are outlined

GaAs Compounds Heteroepitaxy on Silicon for Opto and Nano Electronic Applications

III-V semiconductors present interesting properties and are already used in electronics, lightening and photonic devices. Integration of III-V devices onto a Si CMOS platform is already in production using III-V devices transfer. A promising way consists in using hetero-epitaxy processes to grow the III-V materials directly on Si and at the right place. To reach this objective, some challenges still needed to be overcome. In this contribution, we will show how to overcome the different challenges associated to the heteroepitaxy and integration of III-As onto a silicon platform. We present solutions to get rid of antiphase domains for GaAs grown on exact Si(100). To reduce the threading dislocations density, efficient ways based on either insertion of InGaAs/GaAs multilayers defect filter layers or selective epitaxy in cavities are implemented. All these solutions allows fabricating electrically pumped laser structures based on InAs quantum dots active region, required for photonic and sensing applications

Low threading dislocation density and antiphase boundary free GaAs epitaxially grown on on-axis Si (001) substrates

The interactions between 1D defect threading dislocations and 2D defect antiphase boundaries and antiphase boundary annihilation in III–V materials on Si heteroepitaxy growth are revealed

Design and Characterisation of Multi-Mode Interference Reflector Lasers for Integrated Photonics

InAs quantum dot ridge waveguide lasers comprising single-port multi-mode-interference-reflectors (MMIR) and single-cleaved reflectors are designed, fabricated, and characterised, to demonstrate capability for optoelectronic-integrated-circuits. Simulations of an MMIR show high values of fundamental mode reflectivity ($> 80\% )$ and good selectivity against higher order modes. Deep-etched MMIR lasers fabricated with 0.5 mm long cavities have a threshold current of 24 mA, compared to 75 mA for standard Fabry–Perot cleaved–cleaved FP-RWG lasers of the same length, both at 25 °C, and 56 mA compared to 102 mA at 55 °C. MMIR lasers exhibit stable ground state operation up to 50 °C and show promise as small footprint sources for integrated photonics

The Epitaxial Growth and Unique Morphology of InAs Quantum Dots Embedded in a Ge Matrix

In this work, we investigated the epitaxial growth of InAs quantum dots (QDs) on Ge substrates. By varying the growth parameters of growth temperature, deposition thickness and growth rate of InAs, a high density of 1.2 ×1011 cm-2 self-assembled InAs QDs were successfully epitaxially grown on Ge substrates by solid-source molecular beam epitaxy (MBE) and capped by Ge layers. Pyramidal- and polyhedral-shaped InAs QDs embedded in Ge matrices were revealed, which are distinct from the lens- or truncated pyramid-shape dots in InAs/GaAs or InAs/Si systems. Moreover, with 200 nm Ge capping layer, one third of the embedded QDs are found with ellipse and hexagonal nanovoids with sizes of 7 – 9 nm, which is observed for the first time for InAs QDs embedded in a Ge matrix to the best of our knowledge. These results provide a new possibility of integrating InAs QD devices on Group-IV platforms for Si photonics

Theoretical analysis and modelling of degradation for III–V lasers on Si

Abstract: InAs/GaAs quantum-dot (QD) lasers offer a promising method to realise Si-based on-chip light sources. However, the monolithic integration of III–V materials on Si introduces a high density of threading dislocations (TDs), which limits the performance of such a laser device in terms of device lifetime. Here, we proposed a kinetic model including a degradation term and a saturation term to simulate the degradation process caused by the TDs in the early stage of laser operation. By using a rate equation model, the current density in the wetting layer, where the TDs concentrate, is calculated. We compared the rate of degradation of QD lasers with different cavity lengths and of quantum-well lasers, where both are directly grown on Si substrates, by varying the fitting parameters in the calculation of current densities in the kinetic model