Initial Investigation on the Impact of In Situ Hydrogen Plasma Exposure to the Interface Between Molecular Beam Epitaxially Grown P-Ga_0.7In_0.3Sb (100) and Thermal Atomic Layer Deposited (ALD) Al₂O₃

This work presents, to the best of the authors knowledge, the first experimental findings on the impact of in situ H<sub>2</sub> plasma exposure to the electrical properties of the interface between p-type Ga<sub>0.7</sub>In<sub>0.3</sub>Sb and atomic layer deposited Al<sub>2</sub>O<sub>3</sub>. The effects of trimethyl aluminium (TMA) exposure prior to Al<sub>2</sub>O<sub>3</sub> deposition, and of a post gate metal forming gas anneal (FGA) are also investigated. The control sample, which was subjected to an ex situ HCl clean prior to ALD only, demonstrated a capacitance modulation of 36.29 % before FGA. This degraded for samples exposed to the H<sub>2</sub> plasma for all plasma powers investigated. TMA exposure offered no improvement, and significantly increased the frequency dispersion in accumulation for all samples. A post gate metal FGA at 350 °C for 15 minutes was found to substantially improve the interface quality, with the capacitance modulation, frequency dispersion in accumulation and dC/dV improving by as much as 190 %, 91 %, and 170 % respectively

A new monolithic approach for mid-IR focal plane arrays

Antimonide-based photodetectors have recently been grown on a GaAs substrate by molecular beam epitaxy (MBE) and reported to have comparable performance to the devices grown on more expensive InSb and GaSb substrates. We demonstrated that GaAs, in addition to providing a cost saving substrate for antimonide-based semiconductor growth, can be used as a functional material to fabricate transistors and realize addressing circuits for the heterogeneously grown photodetectors. Based on co-integration of a GaAs MESFET with an InSb photodiode, we recently reported the first demonstration of a switchable and mid-IR sensible photo-pixel on a GaAs substrate that is suitable for large-scale integration into a focal plane array. In this work we report on the fabrication steps that we had to develop to deliver the integrated photo-pixel. Various highly controllable etch processes, both wet and dry etch based, were established for distinct material layers. Moreover, in order to avoid thermally-induced damage to the InSb detectors, a low temperature annealed Ohmic contact was used, and the processing temperature never exceeded 180 °C. Furthermore, since there is a considerable etch step (> 6 μm) that metal must straddle in order to interconnect the fabricated devices, we developed an intermediate step using polyimide to provide a smoothing section between the lower MESFET and upper photodiode regions of the device. This heterogeneous technology creates great potential to realize a new type of monolithic focal plane array of addressable pixels for imaging in the medium wavelength infrared range without the need for flip-chip bonding to a CMOS readout chip

Multispectral mid-infrared light emitting diodes on a GaAs substrate

We have designed, simulated, and experimentally demonstrated four-colour mid-infrared (mid-IR) Light Emitting Diodes (LEDs) integrated monolithically into a vertical structure on a semi-insulating GaAs substrate. In order to finely control the peak wavelength of the emitted mid-IR light, quantum well (QW) structures based on AlInSb/InSb/AlInSb are employed. The completed device structure consists of three p-QW-n diodes with different well widths stacked on top of one bulk AlInSb p-i-n diode. The epitaxial layers comprising the device are designed in such a way that one contact layer is shared between two LEDs. The design of the heterostructure realising the multispectral LEDs was aided by numerical modelling, and good agreement is observed between the simulated and experimental results. Electro-Luminescence measurements, carried out at room temperature, confirm that the emission of each LED peaks at a different wavelength. Peak wavelengths of 3.40 μm, 3.50 μm, 3.95 μm, and 4.18 μm are observed in the bulk, 2 nm, 4 nm, and 6 nm quantum well LEDs, respectively. Under zero bias, Fourier Transform Infrared photo-response measurements indicate that these fabricated diodes can also be operated as mid-IR photodetectors with an extended cut-off wavelength up to 4.6 μm

Usefulness of the SF-36 Health Survey in screening for depressive and anxiety disorders in rheumatoid arthritis

BACKGROUND: This study aimed to assess the accuracy of the Short-Form Health Survey (SF-36) mental health subscale (MH) and mental component summary (MCS) scores in identifying the presence of probable major depressive or anxiety disorder in patients with rheumatoid arthritis. METHODS: SF-36 data were collected in 100 hospital outpatients with rheumatoid arthritis. MH and MCS scores were compared against depression and anxiety data collected using validated measures as part of routine clinical practice. Sensitivity and specificity of the SF-36 were established using receiver operating characteristic (ROC) curve analysis, and area under the curve (AUC) compared the performance of the SF-36 components with the 9-item Patient Health Questionnaire (PHQ9) for depression and the 7-item Generalised Anxiety Disorder (GAD7) questionnaire for anxiety. RESULTS: The MH with a threshold of ≤52 had sensitivity and specificity of 81.0 and 71.4 % respectively to detect anxiety, correctly classifying 73.5 % of patients with probable anxiety disorder. A threshold of ≤56 had sensitivity and specificity of 92.6 and 73.2 % respectively to detect depression, correctly classifying 78.6 % of patients, and the same threshold could also be used to detect either depression or anxiety with a sensitivity of 87.9 %, specificity of 76.9 % and accuracy of 80.6 %. The MCS with a threshold of ≤35 had sensitivity and specificity of 85.7 and 81.9 % respectively to detect anxiety, correctly classifying 82.8 % of patients with probable anxiety disorder. A threshold of ≤40 had sensitivity and specificity of 92.3 and 70.2 % respectively to detect depression, correctly classifying 76.3 % of patients. A threshold of ≤38 could be used to detect either depression or anxiety with a sensitivity of 87.5 %, specificity of 80.3 % and accuracy of 82.8 %. CONCLUSION: This analysis may increase the utility of a widely-used questionnaire. Overall, optimal use of the SF-36 for screening for mental disorder may be through using the MCS with a threshold of ≤38 to identify the presence of either depression or anxiety. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12891-016-1083-y) contains supplementary material, which is available to authorized users

Investigation of mid-infrared AlInSb LEDs with an n-i-p structure

We report on the investigation on mid-infrared AlInSb LEDs with an n-i-p structure. Compared to the conventional AlInSb LEDs with a p-i-n structure, a better current spreading corresponding to a uniform current distribution in the active region is expected in the n-i-p structure because of a high electron mobility in the n-type AlInSb material. The output optical power of laterally injected LEDs were investigated as a function of the device geometry by COMSOL simulations and confirmed by experimental results

LASTA 2.0: validation of a reverse time integration method

Shock tube experiments provide critical insight into the thermochemical processes that occur in the shock layer of hypersonic flight vehicles and are used to validate many chemical-kinetic and radiative models for vehicle design. Shock tube flows exhibit a number of non-ideal behaviours that must be accounted for when interpreting experimental data. Previous work has shown that variations in shock speed and boundary layer growth along the length of the shock tube have a strong effect on the test slug properties. The LAgrangian Shock Tube Analysis code (LASTA) is an a posteriori tool that successfully addressed this problem, allowing reconstruction of the test slug from an experimentally obtained shock trajectory. LASTA 2.0 is presented here, which further constrains the test slug properties using an additional experimental pressure boundary condition whose effects are included via a backwards time integration scheme. The tool is validated against ideal gas cases following accelerating and decelerating shock trajectories, each with a tube-end Mach number of 6.5 and a fill pressure of 66.66 Pa. Agreement between the method and results from a viscous, axisymmetric Navier-Stokes solution is found to be within 1% in pressure and temperature in the majority of cases. Improved agreement with experimental data is evident when compared to the previous version of LASTA, particularly where there is strong shock speed non-uniformity

InSb avalanche photodiodes on GaAs substrates for mid-infrared detection

We present indium antimonide-based devices for mid-infrared (mid-IR) detection with enhanced sensitivity. InSb devices will be useful for many applications, such as gas sensing and imaging. InSb avalanche photodiodes (APDs) monolithically integrated with GaAs substrates were fabricated with diameters ranging from 90 to $200~\mu \text{m}$ and extensively characterized at temperatures ranging from 77 K to 300 K. At 120 K a zero-bias responsivity of 2 A/W was measured, corresponding to a quantum efficiency of 55%. An experimental gain value of 10 at a reverse bias of −3 V was obtained at 120 K, which to the best of our knowledge, is the highest ever reported for InSb APDs. These results pave the way for the development of a monolithically integrated mid-IR array with added gain and wavelength tunability

Brane Gas Inflation

We consider the brane gas picture of the early universe. At later stages, when there are no winding modes and the background is free to expand, we show that a moving 3-brane, which we identify with our universe, can inflate even though it is radiation-dominated. The crucial ingredients for successful inflation are the coupling to the dilaton and the equation of state of the bulk. If we suppose the brane initially forms in a collision of higher-dimensional branes, then the spectrum of primordial density fluctuations naturally has a thermal origin.Comment: 4 pages, 1 figur

Integration techniques of pHEMTs and planar Gunn diodes on GaAs substrates

This work presents two different approaches for the implementation of pseudomorphic high electron mobility transistors (pHEMTs) and planar Gunn diodes on the same gallium arsenide substrate. In the first approach, a combined wafer is used where a buffer layer separates the active layers of the two devices. A second approach was also examined using a single wafer where the AlGaAs/InGaAs/GaAs heterostructures were designed for the realisation of pHEMTs. The comparison between the two techniques showed that the devices fabricated on the single pHEMT wafer presented superior performance over the combined wafer technique. The DC and small-signal characteristics of the pHEMTs on the single wafer were enhanced after the use of T-gates with 70 nm length. The maximum transconductance of the transistors was equal to 780 mS/mm with 200 GHz maximum frequency of oscillation (fmax). Planar Gunn diodes fabricated in the pHEMT wafer, with 1.3 μm anode-to-cathode separation (LAC) presented oscillations at 87.6 GHz with maximum power of oscillation equal to -40 dBm