Tuning InP self-assembled quantum structures to telecom wavelength: A versatile original InP(As) nanostructure "workshop"

The influence of hydride exposure on previously unreported self-assembled InP(As) nanostructures is investigated, showing an unexpected morphological variability with growth parameters, and producing a large family of InP(As) nanostructures by metalorganic vapour phase epitaxy, from dome and ring-like structures to double dot in a ring ensembles. Moreover, preliminary microphotoluminescence data are indicating the capped rings system as an interesting candidate for single quantum emitters at telecom wavelengths, potentially becoming a possible alternative to InAs QDs for quantum technology and telecom applications

Comparison of InGaAs and InAlAs sacrificial layers for release of InP-based devices

Heterogeneous integration of InP devices to Si substrates by adhesive-less micro transfer printing requires flat surfaces for optimum attachment and thermal sinking. InGaAs and InAlAs sacrificial layers are compared for the selective undercut of InP coupons by FeCl3:H2O (1:2). InAlAs offers isotropic etches and superior selectivity (> 4,000) to InP when compared with InGaAs. A 500 nm thick InAlAs sacrificial layer allows the release of wide coupons with a surface roughness < 2 nm and a flatness < 20 nm. The InAlAs release technology is applied to the transfer printing of a pre-fabricated InP laser to a Si substrate

Three-dimensional self-assembled columnar arrays of AlInP quantum wires for polarized micron-sized amber light emitting diodes

A three-dimensional ordered and self-organized semiconductor system emitting highly-polarized light in the yellow-orange visible range (580-650 nm) is presented, comprising self-assembled in-plane AlInP wires vertically stacked in regularly-spaced columns. More than 200 wires per column without detectable defect formation could be stacked. Theoretical simulations and temperature-dependent photoluminescence provided a benchmark to engineer multilayered structures showing internal quantum efficiency at room temperature larger than comparable quantum wells emitting at similar wavelengths. Finally, proof-of-concept light emitting diodes (LED) showed a high degree of light polarization and lower surface parasitic currents than comparable quantum well LEDs, providing an interesting perspective for high-efficiency polarized yellow-orange light emitting devices

Structural and electronic properties of polycrystalline InAs thin films deposited on silicon dioxide and glass at temperatures below 500 °c

Polycrystalline indium arsenide (poly InAs) thin films grown at 475 °C by metal organic vapor phase epitaxy (MOVPE) are explored as possible candidates for low-temperature-grown semiconducting materials. Structural and transport properties of the films are reported, with electron mobilities of ~100 cm2/V·s achieved at room temperature, and values reaching 155 cm2/V·s for a heterostructure including the polycrystalline InAs film. Test structures fabricated with an aluminum oxide (Al2O3) top-gate dielectric show that transistor-type behavior is possible when poly InAs films are implemented as the channel material, with maximum ION/IOFF > 250 achieved at −50 °C and ION/IOFF = 90 at room temperature. Factors limiting the ION/IOFF ratio are investigated and recommendations are made for future implementation of this material

MOVPE metamorphic lasers and nanostructures engineering at telecom wavelengths

In recent years, considerable attention has been drawn to the design of heterostructures on GaAs substrates emitting in the 1.3-µm spectral range for replacing InP injection lasers in medium range fiber-optic communication links. Scaling considerations apart, the enhanced electronic confinement in GaAs-based devices can be expected to reduce carrier leakage at high temperatures, thereby overcoming one of the limiting factors associated with InP-based technologies. InGaAs metamorphic buffer heterostructures constitutes an alternative to the conventional routes relying on quantum dots or dilute nitride approaches, all with their own technical challenges and drawbacks. Metamorphic growth techniques provide compositionally graded buffer layers where the dislocations caused by strain relaxation are confined to the graded layers. However, when grown by metal-organic vapour phase epitaxy (MOVPE), it has been shown as extremely challenging to achieve ∼ 1.3µm emission in InGaAs metamorphic quantum well (QW) lasers (on GaAs substrate), due to a variety of strong, growth related issues, fundamentally linked to the overall epilayer thickness. In this contribution we demonstrate a > 1.3 µm-band laser grown by MOVPE on an engineered metamorphic parabolic graded InxGa1 –xAs buffer. A metamorphic multiple-quantum well structure containing cladding, active, and contact layers was grown. In the cladding, we exploit/control the correlation between epilayer thickness and defect generation and, importantly, demonstrate that the limiting factors introduced by surface instabilities during epitaxy can be managed by an innovative design. The bottom and the upper cladding are built as a combination of AlInGaAs and InGaP alloys in a superlattice (SL) structure. The improved quality of the material was confirmed, for example, by extensive Atomic Force Microscopy (AFM) analyses, showing low roughness (and no direct evidence of defect lines). The heavily compressive strain in QWs and in the metamorphic buffer layer (in combination with the surface step bunched ordering) promoted three-dimensional (3D) features formation under certain growth temperatures and for certain percentage of indium in the QWs. To avoid and control the 3D nanostructuring we proposed as a possible solution the insertion of a GaAs layer deposited before the QW. Moreover, we individuated a range of growth temperature and indium content in the QWs 3D-nanostructures and defects free, verifying the emission of interest. Building on these results, stripe waveguide lasers were fabricated, then characterized electro-optically. Best electro-optical result are reached with modified lower and upper SL cladding structures, adding a graded composition layers at the interfaces following the aim to improve the carrier transport. A 500 µm long and 2.5 µm wide stripe waveguide exhibited a threshold current (Ith) of ∼ 152 mA, corresponding to a density threshold current (Jth) of ∼ 127 mA/cm2 per QWs , operating at room temperature in pulse mode. The turning voltage was ∼ 0.8 V and the resistance series was 4.5 Ω. The emission wavelength was peaked at ∼ 1.34 µm, registered in pulse mode at low duty cycle. With shorter stripes laser, 10 µm and 20 µm wide, with different cavity lengths, we achieved the Light-current-voltage (L-I-V) curves in pulse and continuous wave (CW) mode. The threshold current varied from 130 mA to 170 mA in the operating temperature range of 30 ◦C-80 ◦C, and a characteristic temperature (T0) of 95 K was calculated. The internall loss (αi) and internal quantum efficiency (ηi) extrapolated were ∼ 30 cm−1 and ∼ 57% respectively. Those results prove that the epitaxial structure developed in this thesis work allow to fabricate one the few (specifically the second one, referring to that proposed by a Nippon Telegraph and Telephone Corporation (NTT) Japanese group in 2015 year) InGaAs metamorphic QW laser GaAs based, operating at > 1.3 µm using the MOVPE technology

Macrophage Activation in Follicular Conjunctivitis during the COVID-19 Pandemic

Among the symptoms of SARS-CoV-2, follicular conjunctivitis has become relevant. The conjunctiva acts as an open lymph node, reacting to the viral antigen that binds the epithelial cells, forming follicles of B cells with activated T cells and NK cells on its surface, which, in turn, talk to monocyte-derived inflammatory infected macrophages. Here, the NLRP3 inflammasome is a major driver in releasing pro-inflammatory factors such as IL-6 and caspase-1, leading to follicular conjunctivitis and bulbar congestion, even as isolated signs in the ‘asymptomatic’ patient

Micro-transfer printed InGaAs photodetector on SOI platform

Transfer-printed InGaAs photodetectors are integrated on SOI by evanescent, grating and edge coupling, exhibiting responsivities of 0.7, 0.38 and 0.15 A/W, with dark currents of 48,47 and 400 nA at 0.6 V reverse bias respectively. </p

Dislocation and strain mapping in metamorphic parabolic-graded InGaAs buffers on GaAs

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