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

High Hole Mobility Polycrystalline GaSb Thin Films

In this paper, we report on the structural and electronic properties of polycrystalline gallium antimonide (poly-GaSb) films (50–250 nm) deposited on p+ Si/SiO2 by metalorganic vapour phase epitaxy at 475 °C. GaSb films grown on semi-insulating GaAs substrates are included as comparative samples. In all cases, the unintentionally doped GaSb is p-type, with a hole concentration in the range of 2 × 1016 to 2 × 1017 cm−3. Exceptional hole mobilities are measured for polycrystalline GaSb on SiO2 in the range of 9–66 cm2/Vs, exceeding the reported values for many other semiconductors grown at low temperatures. A mobility of 9.1 cm2/Vs is recorded for an amorphous GaSb layer in a poly-GaAs/amorphous GaSb heterostructure. Mechanisms limiting the mobility in the GaSb thin films are investigated. It is found that for the GaSb grown directly on GaAs, the mobility is phonon-limited, while the GaSb deposited directly on SiO2 has a Coulomb scattering limited mobility, and the poly-GaAs/amorphous GaSb heterostructure on SiO2 displays a mobility which is consistent with variable-range-hopping. GaSb films grown at low temperatures demonstrate a far greater potential for implementation in p-channel devices than for implementation in ICs

Importance of Overcoming MOVPE Surface Evolution Instabilities for &gt;1.3 μm Metamorphic Lasers on GaAs

We investigated and demonstrated a 1.3 $\mu$m-band laser grown by metalorganic vapour phase epitaxy (MOVPE) on a specially engineered metamorphic parabolic graded In$_x$Ga$_{1-x}$As buffer and epitaxial structure on a GaAs substrate. Bottom and upper cladding layers were built as a combination of AlInGaAs and InGaP alloys in a superlattice sequence. This was implemented to overcome (previously unreported) detrimental surface epitaxial dynamics and instabilities: when single alloys are utilised to achieve thick layers on metamorphic structures, surface instabilities induce defect generation. This has represented a historically limiting factor for metamorphic lasers by MOVPE. We describe a number of alternative strategies to achieve smooth surface morphology to obtain efficient compressively strained In$_{0.4}$Ga$_{0.6}$As quantum wells in the active layer. The resulting lasers exhibited low lasing threshold with total slope efficiency of 0.34 W/A for a 500 $\mu$m long ridge waveguide device. The emission wavelength is extended as far as 1360 nm

Risk of Guillain-Barr\ue9 syndrome after 2010-2011 influenza vaccination

Influenza vaccination has been implicated in Guillain Barr\ue9 Syndrome (GBS) although the evidence for this link is controversial. A case-control study was conducted between October 2010 and May 2011 in seven Italian Regions to explore the relation between influenza vaccination and GBS. The study included 176 GBS incident cases aged 6518 years from 86 neurological centers. Controls were selected among patients admitted for acute conditions to the Emergency Department of the same hospital as cases. Each control was matched to a case by sex, age, Region and admission date. Two different analyses were conducted: a matched case-control analysis and a self-controlled case series analysis (SCCS). Case-control analysis included 140 cases matched to 308 controls. The adjusted matched odds ratio (OR) for GBS occurrence within 6 weeks after influenza vaccination was 3.8 (95 % CI: 1.3, 10.5). A much stronger association with gastrointestinal infections (OR = 23.8; 95 % CI 7.3, 77.6) and influenza-like illness or upper respiratory tract infections (OR = 11.5; 95 % CI 5.6, 23.5) was highlighted. The SCCS analysis included all 176 GBS cases. Influenza vaccination was associated with GBS, with a relative risk of 2.1 (95 % CI 1.1, 3.9). According to these results the attributable risk in adults ranges from two to five GBS cases per 1,000,000 vaccinations